Hi, Jan
On Fri 17-03-23 09:35:53, Zhihao Cheng wrote:
Following process makes i_disksize exceed i_size:
generic_perform_write
copied = iov_iter_copy_from_user_atomic(len) // copied < len
ext4_da_write_end
| ext4_update_i_disksize
| new_i_size = pos + copied;
| WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize
| generic_write_end
| copied = block_write_end(copied, len) // copied = 0
| if (unlikely(copied < len))
| if (!PageUptodate(page))
| copied = 0;
| if (pos + copied > inode->i_size) // return false
if (unlikely(copied == 0))
goto again;
if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
status = -EFAULT;
break;
}
We get i_disksize greater than i_size here, which could trigger WARNING
check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio:
ext4_dio_write_iter
iomap_dio_rw
__iomap_dio_rw // return err, length is not aligned to 512
ext4_handle_inode_extension
WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops
WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319
CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2
RIP: 0010:ext4_file_write_iter+0xbc7
Call Trace:
vfs_write+0x3b1
ksys_write+0x77
do_syscall_64+0x39
Fix it by putting block_write_end() before i_disksize updating just
like ext4_write_end() does.
Fetch a reproducer in [Link].
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209
Fixes: 64769240bd07f ("ext4: Add delayed allocation support in
data=writeback mode")
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Good catch (although practically this will hardly have any negative
effect). But rather than opencoding generic_write_end() I'd do:
if (unlikely(copied < len) && !PageUptodate(page))
copied = 0;
at the beginning of ext4_da_write_end() and that should solve these
problems as well?
Yes, your suggestion looks good, and I think we can put the checking
just after ext4_write_inline_data_end(Line 3150)? On the one hand, we
can pass original 'copied' value in trace_ext4_da_write_end(), one the
other hand, ext4_write_inline_data_end() already has this checking.
.
BTW, I want send another patch as follows:
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf0b7dea4900..570a687ae847 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file,
return ext4_write_inline_data_end(inode, pos, len,
copied, page);
start = pos & (PAGE_SIZE - 1);
- end = start + copied - 1;
+ end = start + (copied ? copied - 1 : copied);
/*
* Since we are holding inode lock, we are sure i_disksize <=
@@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file,
* ext4_da_write_inline_data_end().
*/
new_i_size = pos + copied;
- if (copied && new_i_size > inode->i_size &&
+ if (new_i_size > inode->i_size &&
ext4_da_should_update_i_disksize(page, end))
ext4_update_i_disksize(inode, new_i_size);
This modification handle unconsistent i_size and i_disksize imported by
ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()").
Paritially written may display a fake inode size for user, for example:
i_disksize=1
generic_perform_write
copied = iov_iter_copy_from_user_atomic(len) // copied = 0
ext4_da_write_end // skip updating i_disksize
generic_write_end
if (pos + copied > inode->i_size) { // 10 + 0 > 1, true
i_size_write(inode, pos + copied); // i_size = 10
}
0 1 10 4096
|_|_______|_________..._____|
| |
i_size pos
Now, user see the i_size is 10 (i_disksize is still 1). After inode
destroyed, user will get the i_size is 1 read from disk.
