Patch "btrfs: preserve i_mode if __btrfs_set_acl() fails" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

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

    btrfs: preserve i_mode if __btrfs_set_acl() fails

to the 4.9-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:
     btrfs-preserve-i_mode-if-__btrfs_set_acl-fails.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d7d824966530acfe32b94d1ed672e6fe1638cd68 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ernesto=20A=2E=20Fern=C3=A1ndez?=
 <ernesto.mnd.fernandez@gmail.com>
Date: Wed, 2 Aug 2017 03:18:27 -0300
Subject: btrfs: preserve i_mode if __btrfs_set_acl() fails
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>

commit d7d824966530acfe32b94d1ed672e6fe1638cd68 upstream.

When changing a file's acl mask, btrfs_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 restoring the original mode bits if __btrfs_set_acl
fails.

Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/btrfs/acl.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -114,13 +114,17 @@ out:
 int btrfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 {
 	int ret;
+	umode_t old_mode = inode->i_mode;
 
 	if (type == ACL_TYPE_ACCESS && acl) {
 		ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
 		if (ret)
 			return ret;
 	}
-	return __btrfs_set_acl(NULL, inode, acl, type);
+	ret = __btrfs_set_acl(NULL, inode, acl, type);
+	if (ret)
+		inode->i_mode = old_mode;
+	return ret;
 }
 
 /*


Patches currently in stable-queue which might be from ernesto.mnd.fernandez@gmail.com are

queue-4.9/btrfs-preserve-i_mode-if-__btrfs_set_acl-fails.patch