xfs: fix type confusion in xfs_ioc_swapext

Without this check, the following XFS_I invocations would return bad
pointers when used on non-XFS inodes (perhaps pointers into preceding
allocator chunks).

This could be used by an attacker to trick xfs_swap_extents into
performing locking operations on attacker-chosen structures in kernel
memory, potentially leading to code execution in the kernel.  (I have
not investigated how likely this is to be usable for an attack in
practice.)

Signed-off-by: Jann Horn <jann@thejh.net>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index dbca7375deef..63a6ff2cfc68 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1575,6 +1575,12 @@ xfs_ioc_swapext(
                 goto out_put_tmp_file;
         }
 
+        if (f.file->f_op != &xfs_file_operations ||
+            tmp.file->f_op != &xfs_file_operations) {
+                error = -EINVAL;
+                goto out_put_tmp_file;
+        }
+
         ip = XFS_I(file_inode(f.file));
         tip = XFS_I(file_inode(tmp.file));