btrfs: fix use-after-free in mount_subvol()

Pointer 'newargs' is used after the memory that it points to has already
been freed.

Picked up by Coverity - CID 1201425.

Fixes: 0723a0473f ("btrfs: allow mounting btrfs subvolumes with
different ro/rw options")
Signed-off-by: Christoph Jaeger <christophjaeger@linux.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 994c40955315..53bc3733d483 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1186,7 +1186,6 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
                 return ERR_PTR(-ENOMEM);
         mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name,
                              newargs);
-        kfree(newargs);
 
         if (PTR_RET(mnt) == -EBUSY) {
                 if (flags & MS_RDONLY) {
@@ -1196,17 +1195,22 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
                         int r;
                         mnt = vfs_kern_mount(&btrfs_fs_type, flags | MS_RDONLY, device_name,
                                              newargs);
-                        if (IS_ERR(mnt))
+                        if (IS_ERR(mnt)) {
+                                kfree(newargs);
                                 return ERR_CAST(mnt);
+                        }
 
                         r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
                         if (r < 0) {
                                 /* FIXME: release vfsmount mnt ??*/
+                                kfree(newargs);
                                 return ERR_PTR(r);
                         }
                 }
         }
 
+        kfree(newargs);
+
         if (IS_ERR(mnt))
                 return ERR_CAST(mnt);