ext4: fix crashes in dioread_nolock mode

Competing overwrite DIO in dioread_nolock mode will just overwrite
pointer to io_end in the inode. This may result in data corruption or
extent conversion happening from IO completion interrupt because we
don't properly set buffer_defer_completion() when unlocked DIO races
with locked DIO to unwritten extent.

Since unlocked DIO doesn't need io_end for anything, just avoid
allocating it and corrupting pointer from inode for locked DIO.
A cleaner fix would be to avoid these games with io_end pointer from the
inode but that requires more intrusive changes so we leave that for
later.

Cc: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d667447..9cc57c3 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3281,29 +3281,29 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
         * case, we allocate an io_end structure to hook to the iocb.
         */
        iocb->private = NULL;
-       ext4_inode_aio_set(inode, NULL);
-       if (!is_sync_kiocb(iocb)) {
-               io_end = ext4_init_io_end(inode, GFP_NOFS);
-               if (!io_end) {
-                       ret = -ENOMEM;
-                       goto retake_lock;
-               }
-               /*
-                * Grab reference for DIO. Will be dropped in ext4_end_io_dio()
-                */
-               iocb->private = ext4_get_io_end(io_end);
-               /*
-                * we save the io structure for current async direct
-                * IO, so that later ext4_map_blocks() could flag the
-                * io structure whether there is a unwritten extents
-                * needs to be converted when IO is completed.
-                */
-               ext4_inode_aio_set(inode, io_end);
-       }
-
        if (overwrite) {
                get_block_func = ext4_get_block_overwrite;
        } else {
+               ext4_inode_aio_set(inode, NULL);
+               if (!is_sync_kiocb(iocb)) {
+                       io_end = ext4_init_io_end(inode, GFP_NOFS);
+                       if (!io_end) {
+                               ret = -ENOMEM;
+                               goto retake_lock;
+                       }
+                       /*
+                        * Grab reference for DIO. Will be dropped in
+                        * ext4_end_io_dio()
+                        */
+                       iocb->private = ext4_get_io_end(io_end);
+                       /*
+                        * we save the io structure for current async direct
+                        * IO, so that later ext4_map_blocks() could flag the
+                        * io structure whether there is a unwritten extents
+                        * needs to be converted when IO is completed.
+                        */
+                       ext4_inode_aio_set(inode, io_end);
+               }
                get_block_func = ext4_get_block_write;
                dio_flags = DIO_LOCKING;
        }