Commit b9b98c26 authored Feb 19, 2016 by Jan Kara Committed by Greg Kroah-Hartman Apr 24, 2018

ext4: fix crashes in dioread_nolock mode



commit 74dae4278546b897eb81784fdfcce872ddd8b2b8 upstream.

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>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent ba250be9

fs/ext4/inode.c

+20 −20

Original line number	Diff line number	Diff line
		@@ -3256,6 +3256,9 @@ 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;
		if (overwrite) {
		get_block_func = ext4_get_block_write_nolock;
		} else {
		ext4_inode_aio_set(inode, NULL);
		if (!is_sync_kiocb(iocb)) {
		io_end = ext4_init_io_end(inode, GFP_NOFS);
		@@ -3264,7 +3267,8 @@ static ssize_t ext4_ext_direct_IO(struct kiocb iocb, struct iov_iter iter,
		goto retake_lock;
		}
		/*
		* Grab reference for DIO. Will be dropped in ext4_end_io_dio()
		* Grab reference for DIO. Will be dropped in
		* ext4_end_io_dio()
		*/
		iocb->private = ext4_get_io_end(io_end);
		/*
		@@ -3275,10 +3279,6 @@ static ssize_t ext4_ext_direct_IO(struct kiocb iocb, struct iov_iter iter,
		*/
		ext4_inode_aio_set(inode, io_end);
		}

		if (overwrite) {
		get_block_func = ext4_get_block_write_nolock;
		} else {
		get_block_func = ext4_get_block_write;
		dio_flags = DIO_LOCKING;
		}