[PATCH v3] security: Place security_path_post_mknod() where the original IMA call was

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu at huawei.com>

Commit 08abce60d63f ("security: Introduce path_post_mknod hook")
introduced security_path_post_mknod(), to replace the IMA-specific call to
ima_post_path_mknod().

For symmetry with security_path_mknod(), security_path_post_mknod() was
called after a successful mknod operation, for any file type, rather than
only for regular files at the time there was the IMA call.

However, as reported by VFS maintainers, successful mknod operation does
not mean that the dentry always has an inode attached to it (for example,
not for FIFOs on a SAMBA mount).

If that condition happens, the kernel crashes when
security_path_post_mknod() attempts to verify if the inode associated to
the dentry is private.

Move security_path_post_mknod() where the ima_post_path_mknod() call was,
which is obviously correct from IMA/EVM perspective. IMA/EVM are the only
in-kernel users, and only need to inspect regular files.

Reported-by: Steve French <smfrench at gmail.com>
Closes: https://lore.kernel.org/linux-kernel/CAH2r5msAVzxCUHHG8VKrMPUKQHmBpE6K9_vjhgDa1uAvwx4ppw@mail.gmail.com/
Suggested-by: Al Viro <viro at zeniv.linux.org.uk>
Fixes: 08abce60d63f ("security: Introduce path_post_mknod hook")
Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
---
 fs/namei.c          | 7 ++-----
 security/security.c | 4 ++--
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index ceb9ddf8dfdd..c5b2a25be7d0 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4050,6 +4050,8 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 		case 0: case S_IFREG:
 			error = vfs_create(idmap, path.dentry->d_inode,
 					   dentry, mode, true);
+			if (!error)
+				security_path_post_mknod(idmap, dentry);
 			break;
 		case S_IFCHR: case S_IFBLK:
 			error = vfs_mknod(idmap, path.dentry->d_inode,
@@ -4060,11 +4062,6 @@ static int do_mknodat(int dfd, struct filename *name, umode_t mode,
 					  dentry, mode, 0);
 			break;
 	}
-
-	if (error)
-		goto out2;
-
-	security_path_post_mknod(idmap, dentry);
 out2:
 	done_path_create(&path, dentry);
 	if (retry_estale(error, lookup_flags)) {
diff --git a/security/security.c b/security/security.c
index 7e118858b545..0a9a0ac3f266 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1793,11 +1793,11 @@ int security_path_mknod(const struct path *dir, struct dentry *dentry,
 EXPORT_SYMBOL(security_path_mknod);
 
 /**
- * security_path_post_mknod() - Update inode security field after file creation
+ * security_path_post_mknod() - Update inode security after reg file creation
  * @idmap: idmap of the mount
  * @dentry: new file
  *
- * Update inode security field after a file has been created.
+ * Update inode security field after a regular file has been created.
  */
 void security_path_post_mknod(struct mnt_idmap *idmap, struct dentry *dentry)
 {
-- 
2.34.1