Re: [PATCH v2] bcachefs: Fix shift-out-of-bounds in bch2_stripe_to_text

[Zhao Mengmeng]

On 2024/10/9 17:10, Hongbo Li wrote:
> 
> 
> On 2024/10/9 13:43, Zhao Mengmeng wrote:
>> From: Zhao Mengmeng <zhaomengmeng@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Tested-by: syzbot+f8c98a50c323635be65d@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Closes: https://syzkaller.appspot.com/bug?extid=f8c98a50c323635be65d
>> Suggested-by: Hongbo Li <lihongbo22@xxxxxxxxxx>
>> Signed-off-by: Zhao Mengmeng <zhaomengmeng@xxxxxxxxxx>
>> ---
>>   fs/bcachefs/ec.c      | 6 ++++++
>>   fs/bcachefs/errcode.h | 3 ++-
>>   2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
>> index 141a4c63142f..bc5ff1331c6f 100644
>> --- a/fs/bcachefs/ec.c
>> +++ b/fs/bcachefs/ec.c
>> @@ -113,6 +113,12 @@ 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))) {
> 
> csum_granularity_bits should do the left shift.

If use `1 << s->csum_granularity_bits(108)` to do the check, syzbot will still trigger shift-out-of
bounds warning. So better check the bits directly.