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

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 <[email protected]> know about it.

From: =?UTF-8?q?Ernesto=20A=2E=20Fern=C3=A1ndez?=
<[email protected]>
Date: Wed, 2 Aug 2017 03:18:27 -0300
Subject: btrfs: preserve i_mode if __btrfs_set_acl() fails
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Content-Type: text/plain; charset=UTF-8
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From: Ernesto A. Fernández <[email protected]>

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.

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

@@ -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 [email protected] are

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