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Subject[PATCH v1 05/11] landlock: Move filesystem helpers and add a new one
Date
From: Mickaël Salaün <mic@linux.microsoft.com>

Move the SB_NOUSER and IS_PRIVATE dentry check to a standalone
is_nouser_or_private() helper. This will be useful for a following
commit.

Move get_mode_access() and maybe_remove() to make them usable by new
code provided by a following commit.

Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Link: https://lore.kernel.org/r/20220221212522.320243-6-mic@digikod.net
---
security/landlock/fs.c | 87 ++++++++++++++++++++++--------------------
1 file changed, 46 insertions(+), 41 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 9662f9fb3cd0..3886f9ad1a60 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -257,6 +257,18 @@ static inline bool unmask_layers(const struct landlock_rule *const rule,
return false;
}

+static inline bool is_nouser_or_private(const struct dentry *dentry)
+{
+ /*
+ * Allows access to pseudo filesystems that will never be mountable
+ * (e.g. sockfs, pipefs), but can still be reachable through
+ * /proc/<pid>/fd/<file-descriptor> .
+ */
+ return (dentry->d_sb->s_flags & SB_NOUSER) ||
+ (d_is_positive(dentry) &&
+ unlikely(IS_PRIVATE(d_backing_inode(dentry))));
+}
+
static int check_access_path(const struct landlock_ruleset *const domain,
const struct path *const path,
const access_mask_t access_request)
@@ -270,14 +282,7 @@ static int check_access_path(const struct landlock_ruleset *const domain,
return 0;
if (WARN_ON_ONCE(!domain || !path))
return 0;
- /*
- * Allows access to pseudo filesystems that will never be mountable
- * (e.g. sockfs, pipefs), but can still be reachable through
- * /proc/<pid>/fd/<file-descriptor> .
- */
- if ((path->dentry->d_sb->s_flags & SB_NOUSER) ||
- (d_is_positive(path->dentry) &&
- unlikely(IS_PRIVATE(d_backing_inode(path->dentry)))))
+ if (is_nouser_or_private(path->dentry))
return 0;
if (WARN_ON_ONCE(domain->num_layers < 1))
return -EACCES;
@@ -356,6 +361,39 @@ static inline int current_check_access_path(const struct path *const path,
return check_access_path(dom, path, access_request);
}

+static inline access_mask_t get_mode_access(const umode_t mode)
+{
+ switch (mode & S_IFMT) {
+ case S_IFLNK:
+ return LANDLOCK_ACCESS_FS_MAKE_SYM;
+ case 0:
+ /* A zero mode translates to S_IFREG. */
+ case S_IFREG:
+ return LANDLOCK_ACCESS_FS_MAKE_REG;
+ case S_IFDIR:
+ return LANDLOCK_ACCESS_FS_MAKE_DIR;
+ case S_IFCHR:
+ return LANDLOCK_ACCESS_FS_MAKE_CHAR;
+ case S_IFBLK:
+ return LANDLOCK_ACCESS_FS_MAKE_BLOCK;
+ case S_IFIFO:
+ return LANDLOCK_ACCESS_FS_MAKE_FIFO;
+ case S_IFSOCK:
+ return LANDLOCK_ACCESS_FS_MAKE_SOCK;
+ default:
+ WARN_ON_ONCE(1);
+ return 0;
+ }
+}
+
+static inline access_mask_t maybe_remove(const struct dentry *const dentry)
+{
+ if (d_is_negative(dentry))
+ return 0;
+ return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR :
+ LANDLOCK_ACCESS_FS_REMOVE_FILE;
+}
+
/* Inode hooks */

static void hook_inode_free_security(struct inode *const inode)
@@ -549,31 +587,6 @@ static int hook_sb_pivotroot(const struct path *const old_path,

/* Path hooks */

-static inline access_mask_t get_mode_access(const umode_t mode)
-{
- switch (mode & S_IFMT) {
- case S_IFLNK:
- return LANDLOCK_ACCESS_FS_MAKE_SYM;
- case 0:
- /* A zero mode translates to S_IFREG. */
- case S_IFREG:
- return LANDLOCK_ACCESS_FS_MAKE_REG;
- case S_IFDIR:
- return LANDLOCK_ACCESS_FS_MAKE_DIR;
- case S_IFCHR:
- return LANDLOCK_ACCESS_FS_MAKE_CHAR;
- case S_IFBLK:
- return LANDLOCK_ACCESS_FS_MAKE_BLOCK;
- case S_IFIFO:
- return LANDLOCK_ACCESS_FS_MAKE_FIFO;
- case S_IFSOCK:
- return LANDLOCK_ACCESS_FS_MAKE_SOCK;
- default:
- WARN_ON_ONCE(1);
- return 0;
- }
-}
-
/*
* Creating multiple links or renaming may lead to privilege escalations if not
* handled properly. Indeed, we must be sure that the source doesn't gain more
@@ -601,14 +614,6 @@ static int hook_path_link(struct dentry *const old_dentry,
get_mode_access(d_backing_inode(old_dentry)->i_mode));
}

-static inline access_mask_t maybe_remove(const struct dentry *const dentry)
-{
- if (d_is_negative(dentry))
- return 0;
- return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR :
- LANDLOCK_ACCESS_FS_REMOVE_FILE;
-}
-
static int hook_path_rename(const struct path *const old_dir,
struct dentry *const old_dentry,
const struct path *const new_dir,
--
2.35.1
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