ext4: fix race writing to an inline_data file while its xattrs are changing

ext4: fix race writing to an inline_data file while its xattrs are changing

Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=09a379549620f122de3aa4e65df9329976e4cdf5
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2021-40490

commit a54c4613dac1500b40e4ab55199f7c51f028e848 upstream.

The location of the system.data extended attribute can change whenever
xattr_sem is not taken.  So we need to recalculate the i_inline_off
field since it mgiht have changed between ext4_write_begin() and
ext4_write_end().

This means that caching i_inline_off is probably not helpful, so in
the long run we should probably get rid of it and shrink the in-memory
ext4 inode slightly, but let's fix the race the simple way for now.

Cc: stable@kernel.org
Fixes: f19d5870cbf72 ("ext4: add normal write support for inline data")
Reported-by: syzbot+13146364637c7363a7de@syzkaller.appspotmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name ext4-fix-race-writing-to-an-inline_data-file-while-i.patch