[lvc-project] btrfs task hung in `lock_extent` syzbot report and CVE-2024-35784

[Andrey Kalachev]

Hi.

I've check c-repro [1] on 6.1.y branch and found that repro still produce
the crash on 6.1.y. I notice that syzbot bisection result [2]
is incorrect: indeed, the hung was fixed by upstream commit b0ad381fa769
("btrfs: fix deadlock with fiemap and extent locking"). Also,
I saw CVE-2024-35784 [3][4] vulnerability, that have direct relation with that syzbot
report. Therefore, syzbot reproducer provided additional way to check for CVE-2024-35784.

I attempted to fix CVE-2024-35784 in stable 6.1.y (over v6.1.157), and
found that the initial fix commit b0ad381fa769 ("btrfs: fix deadlock with
fiemap and extent locking") introduced regressions [5][6].
IMHO here is the minimum patch series to eliminate CVE-2024-35784 from 6.1.y:

b0ad381fa769 ("btrfs: fix deadlock with fiemap and extent locking") (Initial fix of the CVE-2024-35784)
a1a4a9ca77f1 ("btrfs: fix race between ordered extent completion and fiemap") (Fixes: b0ad381fa769)
978b63f7464a ("btrfs: fix race when detecting delalloc ranges during fiemap") (Fixes: b0ad381fa769)
1cab1375ba6d ("btrfs: reuse cloned extent buffer during fiemap to avoid re-allocations") (Optimization: 978b63f7464a)
53e24158684b ("btrfs: set start on clone before calling copy_extent_buffer_full") (Fixes: 1cab1375ba6d)

Required patches attached.
Only two patches in the series have minor backport modifications due to v6.1.157 btrfs code differences.
The remaining patches are identical to the upstream.

Regards,
AK

Reported-by: syzbot+f8217aae382555004877 at syzkaller.appspotmail.com

----

[1] https://syzkaller.appspot.com/text?tag=ReproC&x=12b4c88b280000
[2] https://syzkaller.appspot.com/bug?extid=f8217aae382555004877
[3] https://lore.kernel.org/all/2024051704-CVE-2024-35784-6dec@gregkh/
[4] https://cve.org/CVERecord/?id=CVE-2024-35784
[5] https://lore.kernel.org/linux-btrfs/cover.1709202499.git.fdmanana@suse.com/
[6] https://lore.kernel.org/all/20240304211551.880347593@linuxfoundation.org/