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Subject[PATCH 5.4 378/388] btrfs: fix overflow when copying corrupt csums for a message
Date
From: Johannes Thumshirn <johannes.thumshirn@wdc.com>

commit 35be8851d172c6e3db836c0f28c19087b10c9e00 upstream.

Syzkaller reported a buffer overflow in btree_readpage_end_io_hook()
when loop mounting a crafted image:

detected buffer overflow in memcpy
------------[ cut here ]------------
kernel BUG at lib/string.c:1129!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 26 Comm: kworker/u4:2 Not tainted 5.9.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: btrfs-endio-meta btrfs_work_helper
RIP: 0010:fortify_panic+0xf/0x20 lib/string.c:1129
RSP: 0018:ffffc90000e27980 EFLAGS: 00010286
RAX: 0000000000000022 RBX: ffff8880a80dca64 RCX: 0000000000000000
RDX: ffff8880a90860c0 RSI: ffffffff815dba07 RDI: fffff520001c4f22
RBP: ffff8880a80dca00 R08: 0000000000000022 R09: ffff8880ae7318e7
R10: 0000000000000000 R11: 0000000000077578 R12: 00000000ffffff6e
R13: 0000000000000008 R14: ffffc90000e27a40 R15: 1ffff920001c4f3c
FS: 0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000557335f440d0 CR3: 000000009647d000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
memcpy include/linux/string.h:405 [inline]
btree_readpage_end_io_hook.cold+0x206/0x221 fs/btrfs/disk-io.c:642
end_bio_extent_readpage+0x4de/0x10c0 fs/btrfs/extent_io.c:2854
bio_endio+0x3cf/0x7f0 block/bio.c:1449
end_workqueue_fn+0x114/0x170 fs/btrfs/disk-io.c:1695
btrfs_work_helper+0x221/0xe20 fs/btrfs/async-thread.c:318
process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
kthread+0x3b5/0x4a0 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Modules linked in:
---[ end trace b68924293169feef ]---
RIP: 0010:fortify_panic+0xf/0x20 lib/string.c:1129
RSP: 0018:ffffc90000e27980 EFLAGS: 00010286
RAX: 0000000000000022 RBX: ffff8880a80dca64 RCX: 0000000000000000
RDX: ffff8880a90860c0 RSI: ffffffff815dba07 RDI: fffff520001c4f22
RBP: ffff8880a80dca00 R08: 0000000000000022 R09: ffff8880ae7318e7
R10: 0000000000000000 R11: 0000000000077578 R12: 00000000ffffff6e
R13: 0000000000000008 R14: ffffc90000e27a40 R15: 1ffff920001c4f3c
FS: 0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f95b7c4d008 CR3: 000000009647d000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

The overflow happens, because in btree_readpage_end_io_hook() we assume
that we have found a 4 byte checksum instead of the real possible 32
bytes we have for the checksums.

With the fix applied:

[ 35.726623] BTRFS: device fsid 815caf9a-dc43-4d2a-ac54-764b8333d765 devid 1 transid 5 /dev/loop0 scanned by syz-repro (215)
[ 35.738994] BTRFS info (device loop0): disk space caching is enabled
[ 35.738998] BTRFS info (device loop0): has skinny extents
[ 35.743337] BTRFS warning (device loop0): loop0 checksum verify failed on 1052672 wanted 0xf9c035fc8d239a54 found 0x67a25c14b7eabcf9 level 0
[ 35.743420] BTRFS error (device loop0): failed to read chunk root
[ 35.745899] BTRFS error (device loop0): open_ctree failed

Reported-by: syzbot+e864a35d361e1d4e29a5@syzkaller.appspotmail.com
Fixes: d5178578bcd4 ("btrfs: directly call into crypto framework for checksumming")
CC: stable@vger.kernel.org # 5.4+
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/disk-io.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -649,16 +649,15 @@ static int btree_readpage_end_io_hook(st
goto err;

if (memcmp_extent_buffer(eb, result, 0, csum_size)) {
- u32 val;
- u32 found = 0;
-
- memcpy(&found, result, csum_size);
+ u8 val[BTRFS_CSUM_SIZE] = { 0 };

read_extent_buffer(eb, &val, 0, csum_size);
btrfs_warn_rl(fs_info,
- "%s checksum verify failed on %llu wanted %x found %x level %d",
+ "%s checksum verify failed on %llu wanted " CSUM_FMT " found " CSUM_FMT " level %d",
fs_info->sb->s_id, eb->start,
- val, found, btrfs_header_level(eb));
+ CSUM_FMT_VALUE(csum_size, val),
+ CSUM_FMT_VALUE(csum_size, result),
+ btrfs_header_level(eb));
ret = -EUCLEAN;
goto err;
}

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