From patchwork Sun Aug 14 19:26:00 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?G=C3=BCnther_Noack?= X-Patchwork-Id: 12942952 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E2F1C25B0F for ; Sun, 14 Aug 2022 19:26:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231530AbiHNT0q (ORCPT ); Sun, 14 Aug 2022 15:26:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58672 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbiHNT0l (ORCPT ); Sun, 14 Aug 2022 15:26:41 -0400 Received: from mail-ej1-x62b.google.com (mail-ej1-x62b.google.com [IPv6:2a00:1450:4864:20::62b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DFF8815A26 for ; Sun, 14 Aug 2022 12:26:39 -0700 (PDT) Received: by mail-ej1-x62b.google.com with SMTP id qn6so10349297ejc.11 for ; Sun, 14 Aug 2022 12:26:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc; bh=NgoJRhhzwyecHWOCTYaoH4uZafs4zwzrtI0+EiRGCXY=; b=QLyQXKyzDohXBZ7X7l5DZ3r63l87UPMKT2+QNKH+62u59Nkxhajfkfcxm1F0N7I68W pumT/XYqxld7YFz8REKgFP6rVi7wdkT8WDjyNz9Hg+UI6O80N7hJh5U+4QxnybKqZ6jC 4x3KxYxhBbrZbUBDIiKo97qxPqjpl60KcH/2TqOheNpG3iVFD2wHCZ78lSXMReXloqDa D1WZ4A9wI1mavgy9Smj56zb+MOJZMbKcrjDtuBsTHJnoAx62AiS9Na94xSe2PDcLr2vN xCUzpcwVZdIH/F+Y/b2KJa48WpIu6Qpq9VBBTuqU21CWTub7S0puKimvg0Y851P+rVzD MZbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=NgoJRhhzwyecHWOCTYaoH4uZafs4zwzrtI0+EiRGCXY=; b=glswn7x7lnvJc2be97HswslReUT+K98dLbv8z9U2MCHYQaIG5A9DRFWPRQM0O4fE2w QBw0N5ncJ+dEa+2cfkB9vMh0VG6cDp0lgVFqdoKCeCquZa8wDDD4Df//X0cLZmDvhIs/ +2gtjir4k8WkGxIm10YsDahvDEaaXwNrhCq/Xd4xEQzU/bIqpn9bUom3YKF0LX/xWq0f hyB3KQD117oyo9wsKOKe+nhpGM2F+4Qmdlik/+wj2ZJTlar/z+X7lAIVAc31l6wfqtwK nDJUhbD4rwBEG1pZTZJYsdsz+cR/Nnz6/WEgPzYlT/yxR49EknrNQRKPFDMPcZvep2sP q+rQ== X-Gm-Message-State: ACgBeo3aaMq3Gfl2NAe3b5Az9PTlTnQ95issf6p+EHugYodlacT78oew gKLpygKq9Zmp6019gZdZYOrraPe+QF0= X-Google-Smtp-Source: AA6agR4EMERUbAByJza6Cw91IXNs+q6EgkhC2Z+Ml3MZ852uT+/e1TJ0GWKbLE7CH9+cHyAb6D6CEQ== X-Received: by 2002:a17:906:8455:b0:730:ce3b:5b13 with SMTP id e21-20020a170906845500b00730ce3b5b13mr8346987ejy.151.1660505198437; Sun, 14 Aug 2022 12:26:38 -0700 (PDT) Received: from nuc.i.gnoack.org ([2a02:168:633b:1:1e69:7aff:fe05:97e6]) by smtp.gmail.com with ESMTPSA id bq24-20020a170906d0d800b0072b2ef2757csm3209066ejb.180.2022.08.14.12.26.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Aug 2022 12:26:38 -0700 (PDT) From: =?utf-8?q?G=C3=BCnther_Noack?= To: linux-security-module@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , James Morris , Paul Moore , "Serge E . Hallyn" , =?utf-8?q?G=C3=BCnther_Noack?= Subject: [PATCH v4 1/4] landlock: Support file truncation Date: Sun, 14 Aug 2022 21:26:00 +0200 Message-Id: <20220814192603.7387-2-gnoack3000@gmail.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220814192603.7387-1-gnoack3000@gmail.com> References: <20220814192603.7387-1-gnoack3000@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: Introduce the LANDLOCK_ACCESS_FS_TRUNCATE flag for file truncation. This flag hooks into the path_truncate LSM hook and covers file truncation using truncate(2), ftruncate(2), open(2) with O_TRUNC, as well as creat(). This change also increments the Landlock ABI version, updates corresponding selftests, and includes minor documentation changes to document the flag. Signed-off-by: Günther Noack --- Documentation/userspace-api/landlock.rst | 10 ++++++++++ include/uapi/linux/landlock.h | 17 ++++++++++++----- security/landlock/fs.c | 9 ++++++++- security/landlock/limits.h | 2 +- security/landlock/syscalls.c | 2 +- tools/testing/selftests/landlock/base_test.c | 2 +- tools/testing/selftests/landlock/fs_test.c | 7 ++++--- 7 files changed, 37 insertions(+), 12 deletions(-) diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst index b8ea59493964..6648e59fabe7 100644 --- a/Documentation/userspace-api/landlock.rst +++ b/Documentation/userspace-api/landlock.rst @@ -380,6 +380,16 @@ by the Documentation/admin-guide/cgroup-v1/memory.rst. Previous limitations ==================== +File truncation (ABI < 3) +------------------------- + +File truncation could not be denied before the third Landlock ABI, so it is +always allowed when using a kernel that only supports the first or second ABI. + +Starting with the Landlock ABI version 3, it is now possible to securely +control truncation thanks to the new `LANDLOCK_ACCESS_FS_TRUNCATE` access +right. + File renaming and linking (ABI 1) --------------------------------- diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 23df4e0e8ace..a2fef267bf34 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -95,8 +95,15 @@ struct landlock_path_beneath_attr { * A file can only receive these access rights: * * - %LANDLOCK_ACCESS_FS_EXECUTE: Execute a file. - * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. + * - %LANDLOCK_ACCESS_FS_WRITE_FILE: Open a file with write access. Note that + * you might additionally need the `LANDLOCK_ACCESS_FS_TRUNCATE` right in + * order to overwrite files with :manpage:`open(2)` using `O_TRUNC` or + * :manpage:`creat(2)`. * - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access. + * - %LANDLOCK_ACCESS_FS_TRUNCATE: Truncate a file through file truncation APIs + * like :manpage:`truncate(2)`, :manpage:`ftruncate(2)`, or + * :manpage:`open(2)` with `O_TRUNC` or :manpage:`creat(2)`. This access right + * is available since the third version of the Landlock ABI. * * A directory can receive access rights related to files or directories. The * following access right is applied to the directory itself, and the @@ -139,10 +146,9 @@ struct landlock_path_beneath_attr { * * It is currently not possible to restrict some file-related actions * accessible through these syscall families: :manpage:`chdir(2)`, - * :manpage:`truncate(2)`, :manpage:`stat(2)`, :manpage:`flock(2)`, - * :manpage:`chmod(2)`, :manpage:`chown(2)`, :manpage:`setxattr(2)`, - * :manpage:`utime(2)`, :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, - * :manpage:`access(2)`. + * :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`chmod(2)`, + * :manpage:`chown(2)`, :manpage:`setxattr(2)`, :manpage:`utime(2)`, + * :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, :manpage:`access(2)`. * Future Landlock evolutions will enable to restrict them. */ /* clang-format off */ @@ -160,6 +166,7 @@ struct landlock_path_beneath_attr { #define LANDLOCK_ACCESS_FS_MAKE_BLOCK (1ULL << 11) #define LANDLOCK_ACCESS_FS_MAKE_SYM (1ULL << 12) #define LANDLOCK_ACCESS_FS_REFER (1ULL << 13) +#define LANDLOCK_ACCESS_FS_TRUNCATE (1ULL << 14) /* clang-format on */ #endif /* _UAPI_LINUX_LANDLOCK_H */ diff --git a/security/landlock/fs.c b/security/landlock/fs.c index ec5a6247cd3e..c57f581a9cd5 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -146,7 +146,8 @@ static struct landlock_object *get_inode_object(struct inode *const inode) #define ACCESS_FILE ( \ LANDLOCK_ACCESS_FS_EXECUTE | \ LANDLOCK_ACCESS_FS_WRITE_FILE | \ - LANDLOCK_ACCESS_FS_READ_FILE) + LANDLOCK_ACCESS_FS_READ_FILE | \ + LANDLOCK_ACCESS_FS_TRUNCATE) /* clang-format on */ /* @@ -1140,6 +1141,11 @@ static int hook_path_rmdir(const struct path *const dir, return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR); } +static int hook_path_truncate(const struct path *const path) +{ + return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE); +} + /* File hooks */ static inline access_mask_t get_file_access(const struct file *const file) @@ -1192,6 +1198,7 @@ static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { LSM_HOOK_INIT(path_symlink, hook_path_symlink), LSM_HOOK_INIT(path_unlink, hook_path_unlink), LSM_HOOK_INIT(path_rmdir, hook_path_rmdir), + LSM_HOOK_INIT(path_truncate, hook_path_truncate), LSM_HOOK_INIT(file_open, hook_file_open), }; diff --git a/security/landlock/limits.h b/security/landlock/limits.h index b54184ab9439..82288f0e9e5e 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -18,7 +18,7 @@ #define LANDLOCK_MAX_NUM_LAYERS 16 #define LANDLOCK_MAX_NUM_RULES U32_MAX -#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_REFER +#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_TRUNCATE #define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1) #define LANDLOCK_NUM_ACCESS_FS __const_hweight64(LANDLOCK_MASK_ACCESS_FS) diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c index 735a0865ea11..f4d6fc7ed17f 100644 --- a/security/landlock/syscalls.c +++ b/security/landlock/syscalls.c @@ -129,7 +129,7 @@ static const struct file_operations ruleset_fops = { .write = fop_dummy_write, }; -#define LANDLOCK_ABI_VERSION 2 +#define LANDLOCK_ABI_VERSION 3 /** * sys_landlock_create_ruleset - Create a new ruleset diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c index da9290817866..72cdae277b02 100644 --- a/tools/testing/selftests/landlock/base_test.c +++ b/tools/testing/selftests/landlock/base_test.c @@ -75,7 +75,7 @@ TEST(abi_version) const struct landlock_ruleset_attr ruleset_attr = { .handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE, }; - ASSERT_EQ(2, landlock_create_ruleset(NULL, 0, + ASSERT_EQ(3, landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION)); ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0, diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index 21a2ce8fa739..cb77eaa01c91 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -399,9 +399,10 @@ TEST_F_FORK(layout1, inval) #define ACCESS_FILE ( \ LANDLOCK_ACCESS_FS_EXECUTE | \ LANDLOCK_ACCESS_FS_WRITE_FILE | \ - LANDLOCK_ACCESS_FS_READ_FILE) + LANDLOCK_ACCESS_FS_READ_FILE | \ + LANDLOCK_ACCESS_FS_TRUNCATE) -#define ACCESS_LAST LANDLOCK_ACCESS_FS_REFER +#define ACCESS_LAST LANDLOCK_ACCESS_FS_TRUNCATE #define ACCESS_ALL ( \ ACCESS_FILE | \ @@ -415,7 +416,7 @@ TEST_F_FORK(layout1, inval) LANDLOCK_ACCESS_FS_MAKE_FIFO | \ LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ LANDLOCK_ACCESS_FS_MAKE_SYM | \ - ACCESS_LAST) + LANDLOCK_ACCESS_FS_REFER) /* clang-format on */ From patchwork Sun Aug 14 19:26:01 2022 Content-Type: text/plain; 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Sun, 14 Aug 2022 12:26:39 -0700 (PDT) Received: from nuc.i.gnoack.org ([2a02:168:633b:1:1e69:7aff:fe05:97e6]) by smtp.gmail.com with ESMTPSA id bq24-20020a170906d0d800b0072b2ef2757csm3209066ejb.180.2022.08.14.12.26.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Aug 2022 12:26:39 -0700 (PDT) From: =?utf-8?q?G=C3=BCnther_Noack?= To: linux-security-module@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , James Morris , Paul Moore , "Serge E . Hallyn" , =?utf-8?q?G=C3=BCnther_Noack?= Subject: [PATCH v4 2/4] selftests/landlock: Selftests for file truncation support Date: Sun, 14 Aug 2022 21:26:01 +0200 Message-Id: <20220814192603.7387-3-gnoack3000@gmail.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220814192603.7387-1-gnoack3000@gmail.com> References: <20220814192603.7387-1-gnoack3000@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: These tests exercise the following truncation operations: * truncate() (truncate by path) * ftruncate() (truncate by file descriptor) * open with the O_TRUNC flag * special case: creat(), which is open with O_CREAT|O_WRONLY|O_TRUNC. in the following scenarios: * Files with read, write and truncate rights. * Files with read and truncate rights. * Files with the truncate right. * Files without the truncate right. In particular, the following scenarios are enforced with the test: * The truncate right is required to use ftruncate, even when the thread already has the right to write to the file. * open() with O_TRUNC requires the truncate right, if it truncates a file. open() already checks security_path_truncate() in this case, and it required no additional check in the Landlock LSM's file_open hook. * creat() requires the truncate right when called with an existing filename. * creat() does *not* require the truncate right when it's creating a new file. Signed-off-by: Günther Noack --- tools/testing/selftests/landlock/fs_test.c | 219 +++++++++++++++++++++ 1 file changed, 219 insertions(+) diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index cb77eaa01c91..7a2ce6cd1a5a 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -58,6 +58,7 @@ static const char file1_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3/f1"; static const char file2_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3/f2"; static const char dir_s3d1[] = TMP_DIR "/s3d1"; +static const char file1_s3d1[] = TMP_DIR "/s3d1/f1"; /* dir_s3d2 is a mount point. */ static const char dir_s3d2[] = TMP_DIR "/s3d1/s3d2"; static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3"; @@ -83,6 +84,7 @@ static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3"; * │   ├── f1 * │   └── f2 * └── s3d1 + *    ├── f1 * └── s3d2 * └── s3d3 */ @@ -208,6 +210,7 @@ static void create_layout1(struct __test_metadata *const _metadata) create_file(_metadata, file1_s2d3); create_file(_metadata, file2_s2d3); + create_file(_metadata, file1_s3d1); create_directory(_metadata, dir_s3d2); set_cap(_metadata, CAP_SYS_ADMIN); ASSERT_EQ(0, mount("tmp", dir_s3d2, "tmpfs", 0, "size=4m,mode=700")); @@ -230,6 +233,7 @@ static void remove_layout1(struct __test_metadata *const _metadata) EXPECT_EQ(0, remove_path(file1_s2d2)); EXPECT_EQ(0, remove_path(file1_s2d1)); + EXPECT_EQ(0, remove_path(file1_s3d1)); EXPECT_EQ(0, remove_path(dir_s3d3)); set_cap(_metadata, CAP_SYS_ADMIN); umount(dir_s3d2); @@ -3023,6 +3027,221 @@ TEST_F_FORK(layout1, proc_pipe) ASSERT_EQ(0, close(pipe_fds[1])); } +/* + * Opens the file and invokes ftruncate(2). + * + * Returns the errno of ftruncate if ftruncate() fails. + * Returns EBADFD if open() or close() fail (should not happen). + * Returns 0 if ftruncate(), open() and close() were successful. + */ +static int test_ftruncate(struct __test_metadata *const _metadata, + const char *const path, int flags) +{ + int res, err, fd; + + fd = open(path, flags | O_CLOEXEC); + if (fd < 0) + return EBADFD; + + res = ftruncate(fd, 10); + err = errno; + + if (close(fd) != 0) + return EBADFD; + + if (res < 0) + return err; + return 0; +} + +/* Invokes truncate(2) and returns the errno or 0. */ +static int test_truncate(const char *const path) +{ + if (truncate(path, 10) < 0) + return errno; + return 0; +} + +/* + * Invokes creat(2) and returns its errno or 0. + * Closes the opened file descriptor on success. + * Returns EBADFD if close() returns an error (should not happen). + */ +static int test_creat(struct __test_metadata *const _metadata, + const char *const path, mode_t mode) +{ + int fd = creat(path, mode); + + if (fd < 0) + return errno; + + if (close(fd) < 0) + return EBADFD; + return 0; +} + +TEST_F_FORK(layout1, truncate) +{ + const char *const file_rwt = file1_s1d1; + const char *const file_rw = file2_s1d1; + const char *const file_rt = file1_s1d2; + const char *const file_t = file2_s1d2; + const char *const file_none = file1_s1d3; + const char *const dir_t = dir_s2d1; + const char *const file_in_dir_t = file1_s2d1; + const char *const dir_w = dir_s3d1; + const char *const file_in_dir_w = file1_s3d1; + const struct rule rules[] = { + { + .path = file_rwt, + .access = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE | + LANDLOCK_ACCESS_FS_TRUNCATE, + }, + { + .path = file_rw, + .access = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE, + }, + { + .path = file_rt, + .access = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_TRUNCATE, + }, + { + .path = file_t, + .access = LANDLOCK_ACCESS_FS_TRUNCATE, + }, + // Implicitly: No access rights for file_none. + { + .path = dir_t, + .access = LANDLOCK_ACCESS_FS_TRUNCATE, + }, + { + .path = dir_w, + .access = LANDLOCK_ACCESS_FS_WRITE_FILE, + }, + {}, + }; + const __u64 handled = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE | + LANDLOCK_ACCESS_FS_TRUNCATE; + const int ruleset_fd = create_ruleset(_metadata, handled, rules); + + ASSERT_LE(0, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + ASSERT_EQ(0, close(ruleset_fd)); + + /* + * Checks read, write and truncate rights: truncation works. + * + * Note: Independent of Landlock, ftruncate(2) on read-only + * file descriptors never works. + */ + EXPECT_EQ(0, test_ftruncate(_metadata, file_rwt, O_WRONLY)); + EXPECT_EQ(EINVAL, test_ftruncate(_metadata, file_rwt, O_RDONLY)); + EXPECT_EQ(0, test_truncate(file_rwt)); + EXPECT_EQ(0, test_open(file_rwt, O_WRONLY | O_TRUNC)); + EXPECT_EQ(0, test_open(file_rwt, O_RDONLY | O_TRUNC)); + + /* Checks read and write rights: no truncate variant works. */ + EXPECT_EQ(EACCES, test_ftruncate(_metadata, file_rw, O_WRONLY)); + EXPECT_EQ(EINVAL, test_ftruncate(_metadata, file_rw, O_RDONLY)); + EXPECT_EQ(EACCES, test_truncate(file_rw)); + EXPECT_EQ(EACCES, test_open(file_rw, O_WRONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_rw, O_RDONLY | O_TRUNC)); + + /* + * Checks read and truncate rights: truncation works. + * + * Note: Files opened in O_RDONLY can get truncated as part of + * the same operation. + */ + EXPECT_EQ(0, test_open(file_rt, O_RDONLY)); + EXPECT_EQ(0, test_open(file_rt, O_RDONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_rt, O_WRONLY)); + EXPECT_EQ(EACCES, test_open(file_rt, O_WRONLY)); + EXPECT_EQ(0, test_truncate(file_rt)); + + /* Checks truncate right: truncate works, but can't open file. */ + EXPECT_EQ(EACCES, test_open(file_t, O_WRONLY)); + EXPECT_EQ(EACCES, test_open(file_t, O_RDONLY)); + EXPECT_EQ(EACCES, test_open(file_t, O_WRONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_t, O_RDONLY | O_TRUNC)); + EXPECT_EQ(0, test_truncate(file_t)); + + /* Checks "no rights" case: No form of truncation works. */ + EXPECT_EQ(EACCES, test_open(file_none, O_WRONLY)); + EXPECT_EQ(EACCES, test_open(file_none, O_RDONLY)); + EXPECT_EQ(EACCES, test_open(file_none, O_WRONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_none, O_RDONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_truncate(file_none)); + + /* Checks truncate right on directory: truncate works on contained files */ + EXPECT_EQ(EACCES, test_open(file_in_dir_t, O_WRONLY)); + EXPECT_EQ(EACCES, test_open(file_in_dir_t, O_RDONLY)); + EXPECT_EQ(EACCES, test_open(file_in_dir_t, O_WRONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_in_dir_t, O_RDONLY | O_TRUNC)); + EXPECT_EQ(0, test_truncate(file_in_dir_t)); + + /* + * Checks creat in dir_w: This requires the truncate right + * when overwriting an existing file, but does not require it + * when the file is new. + */ + EXPECT_EQ(EACCES, test_creat(_metadata, file_in_dir_w, 0600)); + + ASSERT_EQ(0, unlink(file_in_dir_w)); + EXPECT_EQ(0, test_creat(_metadata, file_in_dir_w, 0600)); +} + +/* + * Exercises file truncation when it's not restricted, + * as it was the case before LANDLOCK_ACCESS_FS_TRUNCATE existed. + */ +TEST_F_FORK(layout1, truncate_unhandled) +{ + const char *const file_r = file1_s1d1; + const char *const file_w = file2_s1d1; + const char *const file_none = file1_s1d2; + const struct rule rules[] = { + { + .path = file_r, + .access = LANDLOCK_ACCESS_FS_READ_FILE, + }, + { + .path = file_w, + .access = LANDLOCK_ACCESS_FS_WRITE_FILE, + }, + // Implicitly: No rights for file_none. + {}, + }; + const __u64 handled = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE; + const int ruleset_fd = create_ruleset(_metadata, handled, rules); + + ASSERT_LE(0, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + ASSERT_EQ(0, close(ruleset_fd)); + + /* Checks read right: truncation should work through truncate and open. */ + EXPECT_EQ(0, test_truncate(file_r)); + EXPECT_EQ(0, test_open(file_r, O_RDONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_r, O_WRONLY | O_TRUNC)); + + /* Checks write right: truncation should work through truncate, ftruncate and open. */ + EXPECT_EQ(0, test_truncate(file_w)); + EXPECT_EQ(0, test_ftruncate(_metadata, file_w, O_WRONLY)); + EXPECT_EQ(EACCES, test_open(file_w, O_RDONLY | O_TRUNC)); + EXPECT_EQ(0, test_open(file_w, O_WRONLY | O_TRUNC)); + + /* Checks "no rights" case: truncate works but all open attempts fail. */ + EXPECT_EQ(0, test_truncate(file_none)); + EXPECT_EQ(EACCES, test_open(file_none, O_RDONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_none, O_WRONLY | O_TRUNC)); + EXPECT_EQ(EACCES, test_open(file_none, O_WRONLY)); +} + /* clang-format off */ FIXTURE(layout1_bind) {}; /* clang-format on */ From patchwork Sun Aug 14 19:26:02 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?G=C3=BCnther_Noack?= X-Patchwork-Id: 12942954 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C20B9C25B0E for ; Sun, 14 Aug 2022 19:26:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231364AbiHNT0s (ORCPT ); Sun, 14 Aug 2022 15:26:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58738 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231400AbiHNT0n (ORCPT ); Sun, 14 Aug 2022 15:26:43 -0400 Received: from mail-ej1-x631.google.com (mail-ej1-x631.google.com [IPv6:2a00:1450:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B644B15A38 for ; 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Hallyn" , =?utf-8?q?G=C3=BCnther_Noack?= Subject: [PATCH v4 3/4] samples/landlock: Extend sample tool to support LANDLOCK_ACCESS_FS_TRUNCATE Date: Sun, 14 Aug 2022 21:26:02 +0200 Message-Id: <20220814192603.7387-4-gnoack3000@gmail.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220814192603.7387-1-gnoack3000@gmail.com> References: <20220814192603.7387-1-gnoack3000@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: Update the sandboxer sample to restrict truncate actions. This is automatically enabled by default if the running kernel supports LANDLOCK_ACCESS_FS_TRUNCATE, expect for the paths listed in the LL_FS_RW environment variable. Signed-off-by: Günther Noack --- samples/landlock/sandboxer.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c index 3e404e51ec64..771b6b10d519 100644 --- a/samples/landlock/sandboxer.c +++ b/samples/landlock/sandboxer.c @@ -76,7 +76,8 @@ static int parse_path(char *env_path, const char ***const path_list) #define ACCESS_FILE ( \ LANDLOCK_ACCESS_FS_EXECUTE | \ LANDLOCK_ACCESS_FS_WRITE_FILE | \ - LANDLOCK_ACCESS_FS_READ_FILE) + LANDLOCK_ACCESS_FS_READ_FILE | \ + LANDLOCK_ACCESS_FS_TRUNCATE) /* clang-format on */ @@ -160,10 +161,8 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd, LANDLOCK_ACCESS_FS_MAKE_FIFO | \ LANDLOCK_ACCESS_FS_MAKE_BLOCK | \ LANDLOCK_ACCESS_FS_MAKE_SYM | \ - LANDLOCK_ACCESS_FS_REFER) - -#define ACCESS_ABI_2 ( \ - LANDLOCK_ACCESS_FS_REFER) + LANDLOCK_ACCESS_FS_REFER | \ + LANDLOCK_ACCESS_FS_TRUNCATE) /* clang-format on */ @@ -226,11 +225,17 @@ int main(const int argc, char *const argv[], char *const *const envp) return 1; } /* Best-effort security. */ - if (abi < 2) { - ruleset_attr.handled_access_fs &= ~ACCESS_ABI_2; - access_fs_ro &= ~ACCESS_ABI_2; - access_fs_rw &= ~ACCESS_ABI_2; + switch (abi) { + case 1: + /* Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; + __attribute__((fallthrough)); + case 2: + /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; } + access_fs_ro &= ruleset_attr.handled_access_fs; + access_fs_rw &= ruleset_attr.handled_access_fs; ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); From patchwork Sun Aug 14 19:26:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?G=C3=BCnther_Noack?= X-Patchwork-Id: 12942955 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 528B6C25B06 for ; Sun, 14 Aug 2022 19:26:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231806AbiHNT0z (ORCPT ); Sun, 14 Aug 2022 15:26:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58904 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231503AbiHNT0t (ORCPT ); Sun, 14 Aug 2022 15:26:49 -0400 Received: from mail-ej1-x631.google.com (mail-ej1-x631.google.com [IPv6:2a00:1450:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 654091AF0B for ; Sun, 14 Aug 2022 12:26:48 -0700 (PDT) Received: by mail-ej1-x631.google.com with SMTP id i14so10374171ejg.6 for ; Sun, 14 Aug 2022 12:26:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc; bh=D30SETT0tSv61NCSBcqdH/3/FViIS9vtRY0gOp9asbY=; b=amnGmmKUvtClA6U1tC8lC3wce6Su/U/em4PqSamF6mKKOh5SrUF1WdoDeVB624RKqy nvEdG8wl8OC8Cxzb5/u6BoRU78knZJ2y3cNWrZ7DEaWANyHLe6xFhj/ZKofhdUGUTek4 CENpfNJDwAOynMg5zbiyHGxGbzHxmgD8eDGyTCDMcIfDi/1F2QvdSyeDX2etxUB5LIcj Mq8RT9Bz3q2mm43Nt3UeN7cqIFhMeZJff8eeaYw/UQpwIf5GVz7mMJxcCLGvW0ZSCKKe t2FUhSF0LawR4daxduyihWGY4LKft3vLd1950ygfdlVRHP31kqJtj//+3OwpBwQpL3ub wcBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc; bh=D30SETT0tSv61NCSBcqdH/3/FViIS9vtRY0gOp9asbY=; b=Vmue3b1WZZ4Us2qG1XZHRXLUjZUbNjYfUoFIdp4hcqrReRAbT0bbyupdfUIMUtCO41 bUrqLzcXRihxIWRx6kxqxX/JHrsmwyJUPUrwkVHS4aZniUiFxx+f+BOddO+59oopnQhP F8g6J6YjpE6Cvx/JJG95daaQ16okyVKDUbbUcBBzSe5ckm3wAWPUZDQ3FsxV5Jbw8fPB vCKxQD8OhhFzUY96RusHWOhhBEwfVIEZnaCyfcBf6IHKZbm+oslB9eWf+OQK+UvjON2Y EGiumUSyPZeaZMVBYL6gxHXovkRF1HASlOhOonzQ0AQCsBv9lEUoBHkxziRtVwcnTbmz 9VBQ== X-Gm-Message-State: ACgBeo2UkLQigsW77/0s7aM8EpYPqLMGx5vHY4/xlTulcQg325nTXQCX Zobrc1HyFWGb3562fR+bqxJqHu974/g= X-Google-Smtp-Source: AA6agR56+z/yI4tYbn7j0B92Qdrvyt+dZmsf4wCaqNOHdbZAxMaLHJFjVMidM0khBrViUxdqrQcs1Q== X-Received: by 2002:a17:907:3f85:b0:733:3f0e:2f28 with SMTP id hr5-20020a1709073f8500b007333f0e2f28mr8284701ejc.376.1660505206687; Sun, 14 Aug 2022 12:26:46 -0700 (PDT) Received: from nuc.i.gnoack.org ([2a02:168:633b:1:1e69:7aff:fe05:97e6]) by smtp.gmail.com with ESMTPSA id bq24-20020a170906d0d800b0072b2ef2757csm3209066ejb.180.2022.08.14.12.26.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Aug 2022 12:26:46 -0700 (PDT) From: =?utf-8?q?G=C3=BCnther_Noack?= To: linux-security-module@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , James Morris , Paul Moore , "Serge E . Hallyn" , =?utf-8?q?G=C3=BCnther_Noack?= Subject: [PATCH v4 4/4] landlock: Document Landlock's file truncation support Date: Sun, 14 Aug 2022 21:26:03 +0200 Message-Id: <20220814192603.7387-5-gnoack3000@gmail.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220814192603.7387-1-gnoack3000@gmail.com> References: <20220814192603.7387-1-gnoack3000@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: Use the LANDLOCK_ACCESS_FS_TRUNCATE flag in the tutorial. Adapt the backwards compatibility example and discussion to remove the truncation flag where needed. Point out potential surprising behaviour related to truncate. Signed-off-by: Günther Noack --- Documentation/userspace-api/landlock.rst | 48 +++++++++++++++++++----- 1 file changed, 38 insertions(+), 10 deletions(-) diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst index 6648e59fabe7..3ceb97cbe9d1 100644 --- a/Documentation/userspace-api/landlock.rst +++ b/Documentation/userspace-api/landlock.rst @@ -60,7 +60,8 @@ the need to be explicit about the denied-by-default access rights. LANDLOCK_ACCESS_FS_MAKE_FIFO | LANDLOCK_ACCESS_FS_MAKE_BLOCK | LANDLOCK_ACCESS_FS_MAKE_SYM | - LANDLOCK_ACCESS_FS_REFER, + LANDLOCK_ACCESS_FS_REFER | + LANDLOCK_ACCESS_FS_TRUNCATE, }; Because we may not know on which kernel version an application will be @@ -69,16 +70,26 @@ should try to protect users as much as possible whatever the kernel they are using. To avoid binary enforcement (i.e. either all security features or none), we can leverage a dedicated Landlock command to get the current version of the Landlock ABI and adapt the handled accesses. Let's check if we should -remove the `LANDLOCK_ACCESS_FS_REFER` access right which is only supported -starting with the second version of the ABI. +remove the `LANDLOCK_ACCESS_FS_REFER` and `LANDLOCK_ACCESS_FS_TRUNCATE` access +rights, which are only supported starting with the second and third version of +the ABI. .. code-block:: c int abi; abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION); - if (abi < 2) { - ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; + switch (abi) { + case -1: + perror("The running kernel does not enable to use Landlock"); + return 1; + case 1: + /* Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER; + __attribute__((fallthrough)); + case 2: + /* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */ + ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE; } This enables to create an inclusive ruleset that will contain our rules. @@ -127,8 +138,8 @@ descriptor. It may also be required to create rules following the same logic as explained for the ruleset creation, by filtering access rights according to the Landlock -ABI version. In this example, this is not required because -`LANDLOCK_ACCESS_FS_REFER` is not allowed by any rule. +ABI version. In this example, this is not required because all of the requested +``allowed_access`` rights are already available in ABI 1. We now have a ruleset with one rule allowing read access to ``/usr`` while denying all other handled accesses for the filesystem. The next step is to @@ -251,6 +262,24 @@ To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target process, a sandboxed process should have a subset of the target process rules, which means the tracee must be in a sub-domain of the tracer. +Truncating files +---------------- + +The operations covered by `LANDLOCK_ACCESS_FS_WRITE_FILE` and +`LANDLOCK_ACCESS_FS_TRUNCATE` both change the contents of a file and sometimes +overlap in non-intuitive ways. It is recommended to always specify both of +these together. + +A particularly surprising example is :manpage:`creat(2)`. The name suggests +that this system call requires the rights to create and write files. However, +it also requires the truncate right if an existing file under the same name is +already present. + +It should also be noted that truncating files does not necessarily require the +`LANDLOCK_ACCESS_FS_WRITE_FILE` right. Apart from the obvious +:manpage:`truncate(2)` system call, this can also be done through +:manpage:`open(2)` with the flags `O_RDONLY` and `O_TRUNC`. + Compatibility ============= @@ -386,9 +415,8 @@ File truncation (ABI < 3) File truncation could not be denied before the third Landlock ABI, so it is always allowed when using a kernel that only supports the first or second ABI. -Starting with the Landlock ABI version 3, it is now possible to securely -control truncation thanks to the new `LANDLOCK_ACCESS_FS_TRUNCATE` access -right. +Starting with the Landlock ABI version 3, it is now possible to securely control +truncation thanks to the new `LANDLOCK_ACCESS_FS_TRUNCATE` access right. File renaming and linking (ABI 1) ---------------------------------