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Avoid computing out-of-bounds pointer. #952

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Oct 17, 2021
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Avoid computing out-of-bounds pointer. #952

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2 changes: 1 addition & 1 deletion src/ecdsa_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ static int secp256k1_der_parse_integer(secp256k1_scalar *r, const unsigned char
if (secp256k1_der_read_len(&rlen, sig, sigend) == 0) {
return 0;
}
if (rlen == 0 || *sig + rlen > sigend) {
if (rlen == 0 || rlen > (size_t)(sigend - *sig)) {
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nit, maybe casting rlen to ptrdiff_t is more "correct" (in the standard purist sense)?

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It's UB if that cast to ptrdiff_t overflows, and rlen is attacker-controlled data.

(We have these size_t casts everywhere in the file.)

/* Exceeds bounds or not at least length 1 (X.690-0207 8.3.1). */
return 0;
}
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