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Wed, 13 Nov 2024 12:55:28 -0500 (EST) From: Erin Shepherd Date: Wed, 13 Nov 2024 17:55:23 +0000 Subject: [PATCH v2 1/3] pseudofs: add support for export_ops Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241113-pidfs_fh-v2-1-9a4d28155a37@e43.eu> References: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> In-Reply-To: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> To: Christian Brauner , Alexander Viro , Jan Kara , Chuck Lever Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jeff Layton , Amir Goldstein , linux-nfs@vger.kernel.org, Erin Shepherd X-Mailer: b4 0.14.2 Pseudo-filesystems might reasonably wish to implement the export ops (particularly for name_to_handle_at/open_by_handle_at); plumb this through pseudo_fs_context Reviewed-by: Amir Goldstein Signed-off-by: Erin Shepherd --- fs/libfs.c | 1 + include/linux/pseudo_fs.h | 1 + 2 files changed, 2 insertions(+) diff --git a/fs/libfs.c b/fs/libfs.c index 46966fd8bcf9f042e85d0b66134e59fbef83abfd..698a2ddfd0cb94a8927d1d8a3bb3b3226d6d5476 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -669,6 +669,7 @@ static int pseudo_fs_fill_super(struct super_block *s, struct fs_context *fc) s->s_blocksize_bits = PAGE_SHIFT; s->s_magic = ctx->magic; s->s_op = ctx->ops ?: &simple_super_operations; + s->s_export_op = ctx->eops; s->s_xattr = ctx->xattr; s->s_time_gran = 1; root = new_inode(s); diff --git a/include/linux/pseudo_fs.h b/include/linux/pseudo_fs.h index 730f77381d55f1816ef14adf7dd2cf1d62bb912c..2503f7625d65e7b1fbe9e64d5abf06cd8f017b5f 100644 --- a/include/linux/pseudo_fs.h +++ b/include/linux/pseudo_fs.h @@ -5,6 +5,7 @@ struct pseudo_fs_context { const struct super_operations *ops; + const struct export_operations *eops; const struct xattr_handler * const *xattr; const struct dentry_operations *dops; unsigned long magic; From patchwork Wed Nov 13 17:55:24 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Erin Shepherd X-Patchwork-Id: 13874052 Received: from fhigh-b1-smtp.messagingengine.com (fhigh-b1-smtp.messagingengine.com [202.12.124.152]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 487842AE69; 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Wed, 13 Nov 2024 12:55:31 -0500 (EST) From: Erin Shepherd Date: Wed, 13 Nov 2024 17:55:24 +0000 Subject: [PATCH v2 2/3] exportfs: allow fs to disable CAP_DAC_READ_SEARCH check Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241113-pidfs_fh-v2-2-9a4d28155a37@e43.eu> References: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> In-Reply-To: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> To: Christian Brauner , Alexander Viro , Jan Kara , Chuck Lever Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jeff Layton , Amir Goldstein , linux-nfs@vger.kernel.org, Erin Shepherd X-Mailer: b4 0.14.2 For pidfs, there is no reason to restrict file handle decoding by CAP_DAC_READ_SEARCH. Introduce an export_ops flag that can indicate this Signed-off-by: Erin Shepherd --- fs/fhandle.c | 36 +++++++++++++++++++++--------------- include/linux/exportfs.h | 3 +++ 2 files changed, 24 insertions(+), 15 deletions(-) diff --git a/fs/fhandle.c b/fs/fhandle.c index 82df28d45cd70a7df525f50bbb398d646110cd99..056116e58f43983bc7bb86da170fb554c7a2fac7 100644 --- a/fs/fhandle.c +++ b/fs/fhandle.c @@ -235,26 +235,32 @@ static int do_handle_to_path(struct file_handle *handle, struct path *path, return 0; } -/* - * Allow relaxed permissions of file handles if the caller has the - * ability to mount the filesystem or create a bind-mount of the - * provided @mountdirfd. - * - * In both cases the caller may be able to get an unobstructed way to - * the encoded file handle. If the caller is only able to create a - * bind-mount we need to verify that there are no locked mounts on top - * of it that could prevent us from getting to the encoded file. - * - * In principle, locked mounts can prevent the caller from mounting the - * filesystem but that only applies to procfs and sysfs neither of which - * support decoding file handles. - */ static inline bool may_decode_fh(struct handle_to_path_ctx *ctx, unsigned int o_flags) { struct path *root = &ctx->root; + struct export_operations *nop = root->mnt->mnt_sb->s_export_op; + + if (nop && nop->flags & EXPORT_OP_UNRESTRICTED_OPEN) + return true; + + if (capable(CAP_DAC_READ_SEARCH)) + return true; /* + * Allow relaxed permissions of file handles if the caller has the + * ability to mount the filesystem or create a bind-mount of the + * provided @mountdirfd. + * + * In both cases the caller may be able to get an unobstructed way to + * the encoded file handle. If the caller is only able to create a + * bind-mount we need to verify that there are no locked mounts on top + * of it that could prevent us from getting to the encoded file. + * + * In principle, locked mounts can prevent the caller from mounting the + * filesystem but that only applies to procfs and sysfs neither of which + * support decoding file handles. + * * Restrict to O_DIRECTORY to provide a deterministic API that avoids a * confusing api in the face of disconnected non-dir dentries. * @@ -293,7 +299,7 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh, if (retval) goto out_err; - if (!capable(CAP_DAC_READ_SEARCH) && !may_decode_fh(&ctx, o_flags)) { + if (!may_decode_fh(&ctx, o_flags)) { retval = -EPERM; goto out_path; } diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index 893a1d21dc1c4abc7e52325d7a4cf0adb407f039..459508b53e77ed0597cee217ffe3d82cc7cc11a4 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -247,6 +247,9 @@ struct export_operations { */ #define EXPORT_OP_FLUSH_ON_CLOSE (0x20) /* fs flushes file data on close */ #define EXPORT_OP_ASYNC_LOCK (0x40) /* fs can do async lock request */ +#define EXPORT_OP_UNRESTRICTED_OPEN (0x80) /* FS allows open_by_handle_at + without CAP_DAC_READ_SEARCH + */ unsigned long flags; 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Wed, 13 Nov 2024 12:55:33 -0500 (EST) From: Erin Shepherd Date: Wed, 13 Nov 2024 17:55:25 +0000 Subject: [PATCH v2 3/3] pidfs: implement file handle support Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20241113-pidfs_fh-v2-3-9a4d28155a37@e43.eu> References: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> In-Reply-To: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> To: Christian Brauner , Alexander Viro , Jan Kara , Chuck Lever Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jeff Layton , Amir Goldstein , linux-nfs@vger.kernel.org, Erin Shepherd X-Mailer: b4 0.14.2 On 64-bit platforms, userspace can read the pidfd's inode in order to get a never-repeated PID identifier. On 32-bit platforms this identifier is not exposed, as inodes are limited to 32 bits. Instead expose the identifier via export_fh, which makes it available to userspace via name_to_handle_at In addition we implement fh_to_dentry, which allows userspace to recover a pidfd from a PID file handle. We stash the process' PID in the root pid namespace inside the handle, and use that to recover the pid (validating that pid->ino matches the value in the handle, i.e. that the pid has not been reused). We use the root namespace in order to ensure that file handles can be moved across namespaces; however, we validate that the PID exists in the current namespace before returning the inode. Reviewed-by: Amir Goldstein Signed-off-by: Erin Shepherd --- fs/pidfs.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 61 insertions(+), 1 deletion(-) diff --git a/fs/pidfs.c b/fs/pidfs.c index 80675b6bf88459c22787edaa68db360bdc0d0782..0684a9b8fe71c5205fb153b2714bc9c672045fd5 100644 --- a/fs/pidfs.c +++ b/fs/pidfs.c @@ -1,5 +1,6 @@ // SPDX-License-Identifier: GPL-2.0 #include +#include #include #include #include @@ -347,11 +348,69 @@ static const struct dentry_operations pidfs_dentry_operations = { .d_prune = stashed_dentry_prune, }; +#define PIDFD_FID_LEN 3 + +struct pidfd_fid { + u64 ino; + s32 pid; +} __packed; + +static int pidfs_encode_fh(struct inode *inode, u32 *fh, int *max_len, + struct inode *parent) +{ + struct pid *pid = inode->i_private; + struct pidfd_fid *fid = (struct pidfd_fid *)fh; + + if (*max_len < PIDFD_FID_LEN) { + *max_len = PIDFD_FID_LEN; + return FILEID_INVALID; + } + + fid->ino = pid->ino; + fid->pid = pid_nr(pid); + *max_len = PIDFD_FID_LEN; + return FILEID_INO64_GEN; +} + +static struct dentry *pidfs_fh_to_dentry(struct super_block *sb, + struct fid *gen_fid, + int fh_len, int fh_type) +{ + int ret; + struct path path; + struct pidfd_fid *fid = (struct pidfd_fid *)gen_fid; + struct pid *pid; + + if (fh_type != FILEID_INO64_GEN || fh_len < PIDFD_FID_LEN) + return NULL; + + scoped_guard(rcu) { + pid = find_pid_ns(fid->pid, &init_pid_ns); + if (!pid || pid->ino != fid->ino || pid_vnr(pid) == 0) + return NULL; + + pid = get_pid(pid); + } + + ret = path_from_stashed(&pid->stashed, pidfs_mnt, pid, &path); + if (ret < 0) + return ERR_PTR(ret); + + mntput(path.mnt); + return path.dentry; +} + +static const struct export_operations pidfs_export_operations = { + .encode_fh = pidfs_encode_fh, + .fh_to_dentry = pidfs_fh_to_dentry, + .flags = EXPORT_OP_UNRESTRICTED_OPEN, +}; + static int pidfs_init_inode(struct inode *inode, void *data) { inode->i_private = data; inode->i_flags |= S_PRIVATE; - inode->i_mode |= S_IRWXU; + inode->i_mode |= S_IRWXU | S_IRWXG | S_IRWXO; inode->i_op = &pidfs_inode_operations; inode->i_fop = &pidfs_file_operations; /* @@ -382,6 +441,7 @@ static int pidfs_init_fs_context(struct fs_context *fc) return -ENOMEM; ctx->ops = &pidfs_sops; + ctx->eops = &pidfs_export_operations; ctx->dops = &pidfs_dentry_operations; fc->s_fs_info = (void *)&pidfs_stashed_ops; return 0;