Hi Gustavo,
>>>> While looking into Coverity ID 1357456 I ran into the following piece of code at net/bluetooth/smp.c:166
>>>>
>>>> 166/* The following functions map to the LE SC SMP crypto functions
>>>> 167 * AES-CMAC, f4, f5, f6, g2 and h6.
>>>> 168 */
>>>> 169
>>>> 170static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
>>>> 171 size_t len, u8 mac[16])
>>>> 172{
>>>> 173 uint8_t tmp[16], mac_msb[16], msg_msb[CMAC_MSG_MAX];
>>>> 174 SHASH_DESC_ON_STACK(desc, tfm);
>>>> 175 int err;
>>>> 176
>>>> 177 if (len > CMAC_MSG_MAX)
>>>> 178 return -EFBIG;
>>>> 179
>>>> 180 if (!tfm) {
>>>> 181 BT_ERR("tfm %p", tfm);
>>>> 182 return -EINVAL;
>>>> 183 }
>>>> 184
>
> BTW, what do you think about removing the IF block above?
what do you mean by this?
>>>> 185 desc->tfm = tfm;
>>>> 186 desc->flags = 0;
>>>> 187
>>>> 188 /* Swap key and message from LSB to MSB */
>>>> 189 swap_buf(k, tmp, 16);
>>>> 190 swap_buf(m, msg_msb, len);
>>>> 191
>>>> 192 SMP_DBG("msg (len %zu) %*phN", len, (int) len, m);
>>>> 193 SMP_DBG("key %16phN", k);
>>>> 194
>>>> 195 err = crypto_shash_setkey(tfm, tmp, 16);
>>>> 196 if (err) {
>>>> 197 BT_ERR("cipher setkey failed: %d", err);
>>>> 198 return err;
>>>> 199 }
>>>> 200
>>>> 201 err = crypto_shash_digest(desc, msg_msb, len, mac_msb);
>>>> 202 shash_desc_zero(desc);
>>>> 203 if (err) {
>>>> 204 BT_ERR("Hash computation error %d", err);
>>>> 205 return err;
>>>> 206 }
>>>> 207
>>>> 208 swap_buf(mac_msb, mac, 16);
>>>> 209
>>>> 210 SMP_DBG("mac %16phN", mac);
>>>> 211
>>>> 212 return 0;
>>>> 213}
>>>>
>>>> The issue here is that line 180 implies that pointer tfm might be NULL. If this is the case, there is a potential NULL pointer dereference at line 174 once pointer tfm is indirectly dereferenced inside macro SHASH_DESC_ON_STACK().
>>>>
>>>> My question is if there is any chance that pointer tfm maybe be NULL when calling macro SHASH_DESC_ON_STACK()?
>>>
>>> I think the part you are after is this:
>>>
>>> smp->tfm_cmac = crypto_alloc_shash("cmac(aes)", 0, 0);
>>> if (IS_ERR(smp->tfm_cmac)) {
>>> BT_ERR("Unable to create CMAC crypto context");
>>> crypto_free_cipher(smp->tfm_aes);
>>> kzfree(smp);
>>> return NULL;
>>> }
>>>
>>
>> Yeah, this makes it all clear.
>>
>>> So the tfm_cmac is part of the smp structure. However if there is no cipher, we destroy the smp structure and essentially run without SMP support. So it can not really be called anyway.
>>>
>>
>> What I take from this is that as a general rule, I should first try to identify whether the code I'm debugging is reachable or not, depending on the specific structures and variables I'm interested in.
>>
>>> Maybe commenting this might be a good idea.
>>>
>>
>> Yep, it wouldn't hurt.
Patches are welcome :)
Regards
Marcel
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