linux-kernel - Re: [PATCH 2/2] btrfs: prevent copying too big compressed lzo segment

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Date:   Thu, 10 Feb 2022 15:05:08 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Dāvis Mosāns <davispuh@...il.com>
Cc:     linux-btrfs@...r.kernel.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] btrfs: prevent copying too big compressed lzo segment

On Wed, Feb 02, 2022 at 11:44:55PM +0200, Dāvis Mosāns wrote:
> Compressed length can be corrupted to be a lot larger than memory
> we have allocated for buffer.
> This will cause memcpy in copy_compressed_segment to write outside
> of allocated memory.
> 
> This mostly results in stuck read syscall but sometimes when using
> btrfs send can get #GP
> 
> kernel: general protection fault, probably for non-canonical address 0x841551d5c1000: 0000 [#1] PREEMPT SMP NOPTI
> kernel: CPU: 17 PID: 264 Comm: kworker/u256:7 Tainted: P           OE     5.17.0-rc2-1 #12
> kernel: Workqueue: btrfs-endio btrfs_work_helper [btrfs]
> kernel: RIP: 0010:lzo_decompress_bio (./include/linux/fortify-string.h:225 fs/btrfs/lzo.c:322 fs/btrfs/lzo.c:394) btrfs
> Code starting with the faulting instruction
> ===========================================
>    0:*  48 8b 06                mov    (%rsi),%rax              <-- trapping instruction
>    3:   48 8d 79 08             lea    0x8(%rcx),%rdi
>    7:   48 83 e7 f8             and    $0xfffffffffffffff8,%rdi
>    b:   48 89 01                mov    %rax,(%rcx)
>    e:   44 89 f0                mov    %r14d,%eax
>   11:   48 8b 54 06 f8          mov    -0x8(%rsi,%rax,1),%rdx
> kernel: RSP: 0018:ffffb110812efd50 EFLAGS: 00010212
> kernel: RAX: 0000000000001000 RBX: 000000009ca264c8 RCX: ffff98996e6d8ff8
> kernel: RDX: 0000000000000064 RSI: 000841551d5c1000 RDI: ffffffff9500435d
> kernel: RBP: ffff989a3be856c0 R08: 0000000000000000 R09: 0000000000000000
> kernel: R10: 0000000000000000 R11: 0000000000001000 R12: ffff98996e6d8000
> kernel: R13: 0000000000000008 R14: 0000000000001000 R15: 000841551d5c1000
> kernel: FS:  0000000000000000(0000) GS:ffff98a09d640000(0000) knlGS:0000000000000000
> kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> kernel: CR2: 00001e9f984d9ea8 CR3: 000000014971a000 CR4: 00000000003506e0
> kernel: Call Trace:
> kernel:  <TASK>
> kernel: end_compressed_bio_read (fs/btrfs/compression.c:104 fs/btrfs/compression.c:1363 fs/btrfs/compression.c:323) btrfs
> kernel: end_workqueue_fn (fs/btrfs/disk-io.c:1923) btrfs
> kernel: btrfs_work_helper (fs/btrfs/async-thread.c:326) btrfs
> kernel: process_one_work (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:212 ./include/trace/events/workqueue.h:108 kernel/workqueue.c:2312)
> kernel: worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2455)
> kernel: ? process_one_work (kernel/workqueue.c:2397)
> kernel: kthread (kernel/kthread.c:377)
> kernel: ? kthread_complete_and_exit (kernel/kthread.c:332)
> kernel: ret_from_fork (arch/x86/entry/entry_64.S:301)
> kernel:  </TASK>
> 
> Signed-off-by: Dāvis Mosāns <davispuh@...il.com>

Thanks, added to misc-next. I've swapped the order of the patches so
that it's easier to backport the fix.