frost/secp256k1-zkp
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Fix possible integer overflow in DER parsing

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If we’re in the last loop iteration, then `lenleft == 1` and it could
be the case that `ret == MAX_SIZE`, and so `ret +  lenleft` will
overflow to 0 and the sanity check will not catch it. Then we will
return `(int) MAX_SIZE`, which should be avoided because this value is
implementation-defined. (However, this is harmless because
`(int) MAX_SIZE == -1` on all supported platforms.)
This commit is contained in:
Tim Ruffing 2018-11-01 12:15:28 +01:00
parent 1e6f1f5ad5
commit 3cb057f842
1 changed files with 5 additions and 5 deletions
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10
src/ecdsa_impl.h
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@ -66,7 +66,7 @@ static int secp256k1_der_read_len(const unsigned char **sigp, const unsigned cha
return -1; return -1;
} }
/* X.690-207 8.1.3.5 long form length octets */ /* X.690-207 8.1.3.5 long form length octets */
lenleft = b1 & 0x7F; lenleft = b1 & 0x7F; /* lenleft is at least 1 */
if (lenleft > sigend - *sigp) { if (lenleft > sigend - *sigp) {
return -1; return -1;
} }
@ -82,13 +82,13 @@ static int secp256k1_der_read_len(const unsigned char **sigp, const unsigned cha
} }
while (lenleft > 0) { while (lenleft > 0) {
ret = (ret << 8) | **sigp; ret = (ret << 8) | **sigp;
if (ret + lenleft > (size_t)(sigend - *sigp)) {
/* Result exceeds the length of the passed array. */
return -1;
}
(*sigp)++; (*sigp)++;
lenleft--; lenleft--;
} }
if (ret > (size_t)(sigend - *sigp)) {
/* Result exceeds the length of the passed array. */
return -1;
}
if (ret < 128) { if (ret < 128) {
/* Not the shortest possible length encoding. */ /* Not the shortest possible length encoding. */
return -1; return -1;