6.1-stable review patch. If anyone has any objections, please let me know.
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From: Jan Kara jack@suse.cz
[ 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 --- fs/ext4/file.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 8ebe4dc7b0170..18f5fd2a163b0 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -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); }