Re: [PATCH -next v2 3/6] landlock: add chmod and chown support

Hi,

在 2022/8/27 19:12, Xiu Jianfeng 写道:

Add two flags LANDLOCK_ACCESS_FS_CHMOD and LANDLOCK_ACCESS_FS_CHGRP to support restriction to chmod(2) and chown(2) with landlock.

If these two access rights are set on a directory, they only take effect for its context, not the directory itself.

This patch also change the landlock ABI version from 3 to 4.

Signed-off-by: Xiu Jianfeng xiujianfeng@huawei.com

include/uapi/linux/landlock.h | 10 +++-- security/landlock/fs.c | 43 +++++++++++++++++++- 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 | 6 ++- 6 files changed, 56 insertions(+), 9 deletions(-)

diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 735b1fe8326e..07b73626ff20 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -141,14 +141,16 @@ struct landlock_path_beneath_attr {

• directory) parent. Otherwise, such actions are denied with errno set to
• EACCES. The EACCES errno prevails over EXDEV to let user space
• efficiently deal with an unrecoverable error.

• • • %LANDLOCK_ACCESS_FS_CHMOD: Change the file mode bits of a file.
• • • %LANDLOCK_ACCESS_FS_CHGRP: Change the owner and/or group of a file.
  • .. warning::
  • It is currently not possible to restrict some file-related actions
  • accessible through these syscall families: :manpage:`chdir(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:`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 */

@@ -167,6 +169,8 @@ struct landlock_path_beneath_attr { #define LANDLOCK_ACCESS_FS_MAKE_SYM (1ULL << 12) #define LANDLOCK_ACCESS_FS_REFER (1ULL << 13) #define LANDLOCK_ACCESS_FS_TRUNCATE (1ULL << 14) +#define LANDLOCK_ACCESS_FS_CHMOD (1ULL << 15) +#define LANDLOCK_ACCESS_FS_CHGRP (1ULL << 16) /* clang-format on */ #endif /* _UAPI_LINUX_LANDLOCK_H */ diff --git a/security/landlock/fs.c b/security/landlock/fs.c index 4ef614a4ea22..6ac83d96ada7 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -185,7 +185,9 @@ static struct landlock_object *get_inode_object(struct inode *const inode) LANDLOCK_ACCESS_FS_EXECUTE | \ LANDLOCK_ACCESS_FS_WRITE_FILE | \ LANDLOCK_ACCESS_FS_READ_FILE | \

• LANDLOCK_ACCESS_FS_TRUNCATE)

• LANDLOCK_ACCESS_FS_TRUNCATE | \
• LANDLOCK_ACCESS_FS_CHMOD | \
• LANDLOCK_ACCESS_FS_CHGRP) /* clang-format on */

/* @@ -690,6 +692,31 @@ static inline int current_check_access_path(const struct path *const path, return check_access_path(dom, path, access_request); } +static inline int +current_check_access_path_context_only(const struct path *const path,

• 		       const access_mask_t access_request)
  

+{

• const struct landlock_ruleset *const dom =

• landlock_get_current_domain();
  

• struct path eff_path;
• int ret;
• if (!dom)

• return 0;
  

• eff_path = *path;
• /* if it's dir, check its visible parent. */
• if (d_is_dir(eff_path.dentry)) {

• path_get(&eff_path);
  

• /* dont care if reaches the root or not. */
  

I may made a mistake here, I think it should return -EACCES directly if the walk result is not WALK_CONTINUE.

• walk_to_visible_parent(&eff_path);
  

• ret = current_check_access_path(&eff_path, access_request);
  

• path_put(&eff_path);
  

• } else {

• ret = current_check_access_path(&eff_path, access_request);
  

• }
• return ret;

+}

• static inline access_mask_t get_mode_access(const umode_t mode) { switch (mode & S_IFMT) {

@@ -1177,6 +1204,18 @@ static int hook_path_truncate(const struct path *const path) return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE); } +static int hook_path_chmod(const struct path *const path, umode_t mode) +{

• return current_check_access_path_context_only(path,

• 			LANDLOCK_ACCESS_FS_CHMOD);
  

+}

+static int hook_path_chown(const struct path *const path, kuid_t uid, kgid_t gid) +{

• return current_check_access_path_context_only(path,

• 			LANDLOCK_ACCESS_FS_CHGRP);
  

+}

• /* File hooks */

static inline access_mask_t get_file_access(const struct file *const file) @@ -1230,6 +1269,8 @@ static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { 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(path_chmod, hook_path_chmod),
• LSM_HOOK_INIT(path_chown, hook_path_chown),

LSM_HOOK_INIT(file_open, hook_file_open), }; diff --git a/security/landlock/limits.h b/security/landlock/limits.h index 82288f0e9e5e..7cdd7d467d12 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_TRUNCATE +#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_CHGRP #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 f4d6fc7ed17f..469e0e11735c 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 3 +#define LANDLOCK_ABI_VERSION 4 /**

• 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 72cdae277b02..9f00582f639c 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(3, landlock_create_ruleset(NULL, 0,

• ASSERT_EQ(4, 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 debe2d9ea6cf..f513cd8d9d51 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -404,9 +404,11 @@ TEST_F_FORK(layout1, inval) LANDLOCK_ACCESS_FS_EXECUTE | \ LANDLOCK_ACCESS_FS_WRITE_FILE | \ LANDLOCK_ACCESS_FS_READ_FILE | \

• LANDLOCK_ACCESS_FS_TRUNCATE)

• LANDLOCK_ACCESS_FS_TRUNCATE | \
• LANDLOCK_ACCESS_FS_CHMOD | \
• LANDLOCK_ACCESS_FS_CHGRP)

-#define ACCESS_LAST LANDLOCK_ACCESS_FS_TRUNCATE +#define ACCESS_LAST LANDLOCK_ACCESS_FS_CHGRP #define ACCESS_ALL ( \ ACCESS_FILE | \