[PATCH] fsnotify: add generic perm check for unlink/rmdir

Guowei Du
2022-05-03T18:38:15Z

From: duguowei <duguowei@xiaomi.com>

For now, there have been open/access/open_exec perms for file operation,
so we add new perms check with unlink/rmdir syscall. if one app deletes
any file/dir within pubic area, fsnotify can sends fsnotify_event to
listener to deny that, even if the app have right dac/mac permissions.

Signed-off-by: duguowei <duguowei@xiaomi.com>
---
fs/notify/fsnotify.c | 2 +-
include/linux/fs.h | 2 ++
include/linux/fsnotify.h | 16 ++++++++++++++++
include/linux/fsnotify_backend.h | 6 +++++-
security/security.c | 12 ++++++++++--
security/selinux/hooks.c | 4 ++++
6 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 70a8516b78bc..9c03a5f84be0 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -581,7 +581,7 @@ static __init int fsnotify_init(void)
{
int ret;

- BUILD_BUG_ON(HWEIGHT32(ALL_FSNOTIFY_BITS) != 25);
+ BUILD_BUG_ON(HWEIGHT32(ALL_FSNOTIFY_BITS) != 27);

ret = init_srcu_struct(&fsnotify_mark_srcu);
if (ret)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bbde95387a23..9c661584db7d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -100,6 +100,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
#define MAY_CHDIR 0x00000040
/* called from RCU mode, don't block */
#define MAY_NOT_BLOCK 0x00000080
+#define MAY_UNLINK 0x00000100
+#define MAY_RMDIR 0x00000200

/*
* flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond
diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index bb8467cd11ae..68f5d4aaf1ae 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -80,6 +80,22 @@ static inline int fsnotify_parent(struct dentry *dentry, __u32 mask,
return fsnotify(mask, data, data_type, NULL, NULL, inode, 0);
}

+static inline int fsnotify_path_perm(struct path *path, struct dentry *dentry, __u32 mask)
+{
+ __u32 fsnotify_mask = 0;
+
+ if (!(mask & (MAY_UNLINK | MAY_RMDIR)))
+ return 0;
+
+ if (mask & MAY_UNLINK)
+ fsnotify_mask |= FS_UNLINK_PERM;
+
+ if (mask & MAY_RMDIR)
+ fsnotify_mask |= FS_RMDIR_PERM;
+
+ return fsnotify_parent(dentry, fsnotify_mask, path, FSNOTIFY_EVENT_PATH);
+}
+
/*
* Simple wrappers to consolidate calls to fsnotify_parent() when an event
* is on a file/dentry.
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 0805b74cae44..0e2e240e8234 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -54,6 +54,8 @@
#define FS_OPEN_PERM 0x00010000 /* open event in an permission hook */
#define FS_ACCESS_PERM 0x00020000 /* access event in a permissions hook */
#define FS_OPEN_EXEC_PERM 0x00040000 /* open/exec event in a permission hook */
+#define FS_UNLINK_PERM 0x00080000 /* unlink event in a permission hook */
+#define FS_RMDIR_PERM 0x00100000 /* rmdir event in a permission hook */

#define FS_EXCL_UNLINK 0x04000000 /* do not send events if object is unlinked */
/*
@@ -79,7 +81,9 @@
#define ALL_FSNOTIFY_DIRENT_EVENTS (FS_CREATE | FS_DELETE | FS_MOVE | FS_RENAME)

#define ALL_FSNOTIFY_PERM_EVENTS (FS_OPEN_PERM | FS_ACCESS_PERM | \
- FS_OPEN_EXEC_PERM)
+ FS_OPEN_EXEC_PERM | \
+ FS_UNLINK_PERM | \
+ FS_RMDIR_PERM)

/*
* This is a list of all events that may get sent to a parent that is watching
diff --git a/security/security.c b/security/security.c
index b7cf5cbfdc67..8efc00ec02ed 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1160,16 +1160,24 @@ EXPORT_SYMBOL(security_path_mkdir);

int security_path_rmdir(const struct path *dir, struct dentry *dentry)
{
+ int ret;
if (unlikely(IS_PRIVATE(d_backing_inode(dir->dentry))))
return 0;
- return call_int_hook(path_rmdir, 0, dir, dentry);
+ ret = call_int_hook(path_rmdir, 0, dir, dentry);
+ if (ret)
+ return ret;
+ return fsnotify_path_perm(dir, dentry, MAY_RMDIR);
}

int security_path_unlink(const struct path *dir, struct dentry *dentry)
{
+ int ret;
if (unlikely(IS_PRIVATE(d_backing_inode(dir->dentry))))
return 0;
- return call_int_hook(path_unlink, 0, dir, dentry);
+ ret = call_int_hook(path_unlink, 0, dir, dentry);
+ if (ret)
+ return ret;
+ return fsnotify_path_perm(dir, dentry, MAY_UNLINK);
}
EXPORT_SYMBOL(security_path_unlink);

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e9e959343de9..f0780f0eb903 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1801,8 +1801,12 @@ static int may_create(struct inode *dir,
}

#define MAY_LINK 0
+#ifndef MAY_UNLINK
#define MAY_UNLINK 1
+#endif
+#ifndef MAY_RMDIR
#define MAY_RMDIR 2
+#endif

/* Check whether a task can link, unlink, or rmdir a file/directory. */
static int may_link(struct inode *dir,
--
2.17.1