Re: [PATCH v3] bcachefs: Fix shift-out-of-bounds in bch2_stripe_to_text

[Zhao Mengmeng <zhaomzhao@126.com>]

On 2024/10/10 10:03, Kent Overstreet wrote:
> On Wed, Oct 09, 2024 at 10:07:55PM GMT, Zhao Mengmeng wrote:
>> From: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
>>
>> syzbot report a shift-out-of-bounds issue:
>> ------------[ cut here ]------------
>> UBSAN: shift-out-of-bounds in fs/bcachefs/ec.c:147:2
>> shift exponent 108 is too large for 32-bit type 'unsigned int'
>> ----
>> Here s.csum_granularity_bits = 108, so shift is impossible for unsigned
>> int. To fix, add a check in bch2_stripe_validate() to bail out, it has
>> same checking logic with ec_stripe_key_init().
>>
>> Reported-by: syzbot+f8c98a50c323635be65d@syzkaller.appspotmail.com
>> Tested-by: syzbot+f8c98a50c323635be65d@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=f8c98a50c323635be65d
>> Suggested-by: Hongbo Li <lihongbo22@huawei.com>
>> Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
>> ---
>>  fs/bcachefs/ec.c      | 6 ++++++
>>  fs/bcachefs/errcode.h | 4 +++-
>>  2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
>> index 564841e5a24b..f6a02123144d 100644
>> --- a/fs/bcachefs/ec.c
>> +++ b/fs/bcachefs/ec.c
>> @@ -114,6 +114,12 @@ int bch2_stripe_validate(struct bch_fs *c, struct bkey_s_c k,
>>  	const struct bch_stripe *s = bkey_s_c_to_stripe(k).v;
>>  	int ret = 0;
>>  
>> +	if (s->csum_granularity_bits >= ilog2(le16_to_cpu(s->sectors))) {
>> +		bch_err_ratelimited(c, "stripe csum gran bits %u too big",
>> +				    s->csum_granularity_bits);
>> +		return -BCH_ERR_stripe_csum_granularity_bits_too_big;
>> +	}
>> +
> 
> that should be a bkey_fsck_err_on(), and you'll add to the enum in
> sb-errors_format.h

Hi Kent, I try to use bkey_fsck_err_on() at the first time, but it still triggered
syzbot warning, cause bch2_stripe_to_text() is called before __bch2_fsck_err(), before
it throws new errro, it will trigger the shift out of bounds check.

Cheers!