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
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Git-commit: d7d824966530acfe32b94d1ed672e6fe1638cd68
Patch-mainline: v4.14-rc1
References: bsc#1083000

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>
Acked-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/acl.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
index 8d8370ddb6b2..1ba49ebe67da 100644
--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -114,13 +114,17 @@ static int __btrfs_set_acl(struct btrfs_trans_handle *trans,
 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;
 }
 
 /*