Hi developers,
I find a bug in function AES_cfbr_encrypt_block in openssl-0.9.7m. The bug is
memory-reading out-of-bound. The following is the code of function
AES_cfbr_encrypt_block, which is in file crypto/aes/aes_cfb.c
159 /* This expects a single block of size nbits for both in and out. Note that
160 it corrupts any extra bits in the last byte of out */
161 void AES_cfbr_encrypt_block(const unsigned char *in,unsigned char *out,
162 const int nbits,const AES_KEY *key,
163 unsigned char *ivec,const int enc)
164 {
165 int n,rem,num;
166 unsigned char ovec[AES_BLOCK_SIZE*2];
167
168 if (nbits<=0 || nbits>128) return;
169
170 /* fill in the first half of the new IV with the current IV */
171 memcpy(ovec,ivec,AES_BLOCK_SIZE);
172 /* construct the new IV */
173 AES_encrypt(ivec,ivec,key);
174 num = (nbits+7)/8;
175 if (enc) /* encrypt the input */
176 for(n=0 ; n < num ; ++n)
177 out[n] = (ovec[AES_BLOCK_SIZE+n] = in[n] ^ ivec[n]);
178 else /* decrypt the input */
179 for(n=0 ; n < num ; ++n)
180 out[n] = (ovec[AES_BLOCK_SIZE+n] = in[n]) ^ ivec[n];
181 /* shift ovec left... */
182 rem = nbits%8;
183 num = nbits/8;
184 if(rem==0)
185 memcpy(ivec,ovec+num,AES_BLOCK_SIZE);
186 else
187 for(n=0 ; n < AES_BLOCK_SIZE ; ++n)
188 ivec[n] = ovec[n+num]<>(8-rem);
189
190 /* it is not necessary to cleanse ovec, since the IV is not secret */
191 }
If input-parameter nbits is 128, line 183 will set variable num to 16. In the
for loop in line 187, when the induction-variable n increases to 15 (namely
AES_BLOCK_SIZE-1), the program will still go to line 188. The express
"ovec[n+num+1]" will read ovec[32]. However, size of array ovec is only 32
(line 166). So the memory-reading will be out-of-bound.
Would you please study it?
Best Regards
Yiqun Ren (Luke)
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