Commit a3fc765d authored Jun 06, 2024 by Jan Kara Committed by Yang Erkun Jun 06, 2024

ext4: fix warning in ext4_dio_write_end_io()

mainline inclusion
from mainline-v6.7-rc2
commit 619f75dae2cf117b1d07f27b046b9ffb071c4685
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9VOEK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=619f75dae2cf117b1d07f27b046b9ffb071c4685



--------------------------------

The syzbot has reported that it can hit the warning in
ext4_dio_write_end_io() because i_size < i_disksize. Indeed the
reproducer creates a race between DIO IO completion and truncate
expanding the file and thus ext4_dio_write_end_io() sees an inconsistent
inode state where i_disksize is already updated but i_size is not
updated yet. Since we are careful when setting up DIO write and consider
it extending (and thus performing the IO synchronously with i_rwsem held
exclusively) whenever it goes past either of i_size or i_disksize, we
can use the same test during IO completion without risking entering
ext4_handle_inode_extension() without i_rwsem held. This way we make it
obvious both i_size and i_disksize are large enough when we report DIO
completion without relying on unreliable WARN_ON.

Reported-by:  <syzbot+47479b71cdfc78f56d30@syzkaller.appspotmail.com>
Fixes: 91562895f803 ("ext4: properly sync file size update after O_SYNC direct IO")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20231130095653.22679-1-jack@suse.cz


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Yang Erkun <yangerkun@huawei.com>

parent 52c6fec9

fs/ext4/file.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -326,9 +326,10 @@ static void ext4_inode_extension_cleanup(struct inode *inode, ssize_t count)
		return;
		}
		/*
		* If i_disksize got extended due to writeback of delalloc blocks while
		* the DIO was running we could fail to cleanup the orphan list in
		* ext4_handle_inode_extension(). Do it now.
		* If i_disksize got extended either due to writeback of delalloc
		* blocks or extending truncate while the DIO was running we could fail
		* to cleanup the orphan list in ext4_handle_inode_extension(). Do it
		* now.
		*/
		if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) {
		handle_t *handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
		@@ -363,10 +364,11 @@ static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size,
		* blocks. But the code in ext4_iomap_alloc() is careful to use
		* zeroed/unwritten extents if this is possible; thus we won't leave
		* uninitialized blocks in a file even if we didn't succeed in writing
		* as much as we intended.
		* as much as we intended. Also we can race with truncate or write
		* expanding the file so we have to be a bit careful here.
		*/
		WARN_ON_ONCE(i_size_read(inode) < READ_ONCE(EXT4_I(inode)->i_disksize));
		if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize))
		if (pos + size <= READ_ONCE(EXT4_I(inode)->i_disksize) &&
		pos + size <= i_size_read(inode))
		return size;
		return ext4_handle_inode_extension(inode, pos, size);
		}