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ext4: fix warning in ext4_dio_write_end_io() 

[ Upstream commit 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: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jan Kara 2023-11-30 10:56:53 +01:00 committed by Greg Kroah-Hartman
parent 1c077acf24
commit 8925ab33b3
1 changed files with 8 additions and 6 deletions
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14
fs/ext4/file.c
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@ -339,9 +339,10 @@ 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);
@ -376,10 +377,11 @@ 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);
}