Re: [PATCH 4.4.y v2] crypto: algif_skcipher - use ZERO_OR_NULL_PTR in skcipher_recvmsg_async

[yangerkun <yangerkun@huawei.com>]

On 2020/3/8 8:19, Sasha Levin wrote:
> On Sat, Mar 07, 2020 at 09:49:25AM +0800, yangerkun wrote:
>>
>>
>> On 2020/3/6 21:39, Sasha Levin wrote:
>>> On Thu, Mar 05, 2020 at 04:57:55PM +0800, yangerkun wrote:
>>>> Nowdays, we trigger a oops:
>>>> ...
>>>> kasan: GPF could be caused by NULL-ptr deref or user memory 
>>>> accessgeneral protection fault: 0000 [#1] SMP KASAN
>>>> ...
>>>> Call Trace:
>>>> [<ffffffff81a26fb1>] skcipher_recvmsg_async+0x3f1/0x1400 
>>>> x86/../crypto/algif_skcipher.c:543
>>>> [<ffffffff81a28053>] skcipher_recvmsg+0x93/0x7f0 
>>>> x86/../crypto/algif_skcipher.c:723
>>>> [<ffffffff823e43a4>] sock_recvmsg_nosec x86/../net/socket.c:702 
>>>> [inline]
>>>> [<ffffffff823e43a4>] sock_recvmsg x86/../net/socket.c:710 [inline]
>>>> [<ffffffff823e43a4>] sock_recvmsg+0x94/0xc0 x86/../net/socket.c:705
>>>> [<ffffffff823e464b>] sock_read_iter+0x27b/0x3a0 x86/../net/socket.c:787
>>>> [<ffffffff817f479b>] aio_run_iocb+0x21b/0x7a0 x86/../fs/aio.c:1520
>>>> [<ffffffff817f57c9>] io_submit_one x86/../fs/aio.c:1630 [inline]
>>>> [<ffffffff817f57c9>] do_io_submit+0x6b9/0x10b0 x86/../fs/aio.c:1688
>>>> [<ffffffff817f902d>] SYSC_io_submit x86/../fs/aio.c:1713 [inline]
>>>> [<ffffffff817f902d>] SyS_io_submit+0x2d/0x40 x86/../fs/aio.c:1710
>>>> [<ffffffff828b33c3>] tracesys_phase2+0x90/0x95
>>>>
>>>> In skcipher_recvmsg_async, we use '!sreq->tsg' to determine does we
>>>> calloc fail. However, kcalloc may return ZERO_SIZE_PTR, and with this,
>>>> the latter sg_init_table will trigger the bug. Fix it be use 
>>>> ZERO_OF_NULL_PTR.
>>>>
>>>> This function was introduced with ' commit a596999b7ddf ("crypto:
>>>> algif - change algif_skcipher to be asynchronous")', and has been 
>>>> removed
>>>> with 'commit e870456d8e7c ("crypto: algif_skcipher - overhaul memory
>>>> management")'.
>>>>
>>>> Reported-by: Hulk Robot <hulkci@huawei.com>
>>>> Signed-off-by: yangerkun <yangerkun@huawei.com>
>>>> ---
>>>> crypto/algif_skcipher.c | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> v1->v2:
>>>> update the commit message
>>>>
>>>> diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
>>>> index d12782dc9683..9bd4691cc5c5 100644
>>>> --- a/crypto/algif_skcipher.c
>>>> +++ b/crypto/algif_skcipher.c
>>>> @@ -538,7 +538,7 @@ static int skcipher_recvmsg_async(struct socket 
>>>> *sock, struct msghdr *msg,
>>>>     lock_sock(sk);
>>>>     tx_nents = skcipher_all_sg_nents(ctx);
>>>>     sreq->tsg = kcalloc(tx_nents, sizeof(*sg), GFP_KERNEL);
>>>> -    if (unlikely(!sreq->tsg))
>>>> +    if (unlikely(ZERO_OR_NULL_PTR(sreq->tsg)))
>>>
>>> I'm a bit confused: kcalloc() will return ZERO_SIZE_PTR for allocations
>>> that ask for 0 bytes, but here we ask for "sizeof(*sg)" bytes, which is
>>> guaranteed to be more than 0, no?
>>
>> Actually, the size need to calloc is (tx_nents * sizeof(*sg)), and 
>> tx_nents is 0.
> 
> Makes sense. This is also needed on 4.9, right?

Yes! Thanks for checking it!
>