Patch "ext4: preserve i_mode if __ext4_set_acl() fails" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

ext4: preserve i_mode if __ext4_set_acl() fails

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     ext4-preserve-i_mode-if-__ext4_set_acl-fails.patch

and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Ernesto=20A=2E=20Fern=C3=A1ndez?= <[email protected]>
Date: Sun, 30 Jul 2017 22:43:41 -0400
Subject: ext4: preserve i_mode if __ext4_set_acl() fails
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Ernesto A. Fernández <[email protected]>

commit 397e434176bb62bc6068d2210af1d876c6212a7e upstream.

When changing a file's acl mask, __ext4_set_acl() will first set the group bits of i_mode to the value of the mask, and only then set the actual extended attribute representing the new acl.

If the second part fails (due to lack of space, for example) and the file had no acl attribute to begin with, the system will from now on assume that the mask permission bits are actual group permission bits, potentially granting access to the wrong users.

Prevent this by only changing the inode mode after the acl has been set.

---
 fs/ext4/acl.c |   15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

@@ -189,16 +189,17 @@ __ext4_set_acl(handle_t *handle, struct
 	void *value = NULL;
 	size_t size = 0;
 	int error;
+	int update_mode = 0;
+	umode_t mode = inode->i_mode;
 
 	switch (type) {
 	case ACL_TYPE_ACCESS:
 		name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS;
 		if (acl) {
-			error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+			error = posix_acl_update_mode(inode, &mode, &acl);
 			if (error)
 				return error;
-			inode->i_ctime = current_time(inode);
-			ext4_mark_inode_dirty(handle, inode);
+			update_mode = 1;
 		}
 		break;
 

@@ -221,8 +222,14 @@ __ext4_set_acl(handle_t *handle, struct
 				      value, size, 0);
 
 	kfree(value);
-	if (!error)
+	if (!error) {
 		set_cached_acl(inode, type, acl);
+		if (update_mode) {
+			inode->i_mode = mode;
+			inode->i_ctime = current_time(inode);
+			ext4_mark_inode_dirty(handle, inode);
+		}
+	}
 
 	return error;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/ext4-preserve-i_mode-if-__ext4_set_acl-fails.patch