| Message ID | 20220804193746.9161-2-gnoack3000@gmail.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | landlock: truncate support | expand |
On 04/08/2022 21:37, Günther Noack wrote: > 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 <gnoack3000@gmail.com> > --- > Documentation/userspace-api/landlock.rst | 6 ++++++ > 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, 33 insertions(+), 12 deletions(-) > > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst > index b8ea59493964..d92e335380d4 100644 > --- a/Documentation/userspace-api/landlock.rst > +++ b/Documentation/userspace-api/landlock.rst > @@ -380,6 +380,12 @@ 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. I think this addition could make the documentation more consistent and helpful: 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..1beb8289708d 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 Please use backquotes for code such as `LANDLOCK_ACCESS_FS_TRUNCATE`, `O_TRUNC`… > + * 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 */
On Thu, Aug 11, 2022 at 06:59:28PM +0200, Mickaël Salaün wrote: > > On 04/08/2022 21:37, Günther Noack wrote: > > 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 <gnoack3000@gmail.com> > > --- > > Documentation/userspace-api/landlock.rst | 6 ++++++ > > 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, 33 insertions(+), 12 deletions(-) > > > > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst > > index b8ea59493964..d92e335380d4 100644 > > --- a/Documentation/userspace-api/landlock.rst > > +++ b/Documentation/userspace-api/landlock.rst > > @@ -380,6 +380,12 @@ 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. > > I think this addition could make the documentation more consistent and > helpful: > > 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. Agreed, I added that sentence. > > > > + > > File renaming and linking (ABI 1) > > --------------------------------- > > diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h > > index 23df4e0e8ace..1beb8289708d 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 > > Please use backquotes for code such as `LANDLOCK_ACCESS_FS_TRUNCATE`, > `O_TRUNC`… Done. > > > > + * 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 */ --
diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst index b8ea59493964..d92e335380d4 100644 --- a/Documentation/userspace-api/landlock.rst +++ b/Documentation/userspace-api/landlock.rst @@ -380,6 +380,12 @@ 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. + File renaming and linking (ABI 1) --------------------------------- diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 23df4e0e8ace..1beb8289708d 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 */
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 <gnoack3000@gmail.com> --- Documentation/userspace-api/landlock.rst | 6 ++++++ 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, 33 insertions(+), 12 deletions(-)