linux-kernel - Re: [syzbot] KASAN: use-after-free Read in copy_page_from_iter

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Date:   Mon, 13 Jun 2022 21:39:12 +0200
From:   David Sterba <dsterba@...e.cz>
To:     syzbot <syzbot+d2dd123304b4ae59f1bd@...kaller.appspotmail.com>
Cc:     akpm@...ux-foundation.org, clm@...com, dsterba@...e.com,
        hch@....de, josef@...icpanda.com, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
        willy@...radead.org
Subject: Re: [syzbot] KASAN: use-after-free Read in
 copy_page_from_iter_atomic (2)

On Fri, Jun 10, 2022 at 12:10:19AM -0700, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 4cd4aed63125ccd4efc35162627827491c2a7be7
> Author: Christoph Hellwig <hch@....de>
> Date:   Fri May 27 08:43:20 2022 +0000
> 
>     btrfs: fold repair_io_failure into btrfs_repair_eb_io_failure

Josef also reported a crash and found a bug in the patch, now added as
fixup that'll be in for-next:

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 89a319e65197..5eac9ffb7499 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2260,7 +2260,7 @@ int btrfs_repair_eb_io_failure(const struct extent_buffer *eb, int mirror_num)
		__bio_add_page(&bio, p, PAGE_SIZE, start - page_offset(p));
		ret = btrfs_map_repair_bio(fs_info, &bio, mirror_num);
		bio_uninit(&bio);
-
+               start += PAGE_SIZE;
		if (ret)
			return ret;
	}
---