This is a rewrite of Tobias Stoeckmann’s patch from June 2016[1] using functions instead of macros. (Thanks to Tobias for explanations of his patch.) A short question on Freenode IRC showed that macros are generally discouraged and functions should be used.
The patch introduces size_t length_check() and applies it to libalpm/signing.c and signing.h. Feedback is very appreciated. [1] Original patch: https://lists.archlinux.org/pipermail/pacman-dev/2016-June/021148.html CVE request (and assignment): http://seclists.org/oss-sec/2016/q2/526 diff --git a/lib/libalpm/signing.c b/lib/libalpm/signing.c index 95cb3280..f7a9c9a8 100644 --- a/lib/libalpm/signing.c +++ b/lib/libalpm/signing.c @@ -986,6 +986,19 @@ int SYMEXPORT alpm_siglist_cleanup(alpm_siglist_t *siglist) return 0; } +/* Check to avoid out of boundary reads */ +size_t length_check(size_t length, size_t position, size_t a, + alpm_handle_t *handle, const char *identifier) +{ + if( a == 0 || length - position <= a) + { + _alpm_log(handle, ALPM_LOG_ERROR, \ + _("%s: signature format error"), identifier); + return -1; + } + else return 0; +} + /** * Extract the Issuer Key ID from a signature * @param sig PGP signature @@ -1021,19 +1034,22 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, } switch(sig[pos] & 0x03) { - case 0: - blen = sig[pos + 1]; - pos = pos + 2; + case 0: if( length_check(len, pos, 1, handle, identifier) ){ return -1; } + else blen = sig[pos + 1]; + if( length_check(len, pos, 2, handle, identifier) ){ return -1; } + else pos = pos + 2; break; - case 1: - blen = (sig[pos + 1] << 8) | sig[pos + 2]; - pos = pos + 3; + if( length_check(len, pos, 2, handle, identifier) ){ return -1; } + else blen = (sig[pos + 1] << 8) | sig[pos + 2]; + if( length_check(len, pos, 3, handle, identifier) ){ return -1; } + else pos = pos + 3; break; - case 2: - blen = (sig[pos + 1] << 24) | (sig[pos + 2] << 16) | (sig[pos + 3] << 8) | sig[pos + 4]; - pos = pos + 5; + case 2: if( length_check(len, pos, 4, handle, identifier) ){ return -1; } + else blen = (sig[pos + 1] << 24) | (sig[pos + 2] << 16) | (sig[pos + 3] << 8) | sig[pos + 4]; + if( length_check(len, pos, 5, handle, identifier) ){ return -1; } + else pos = pos + 5; break; case 3: @@ -1057,25 +1073,38 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, return -1; } - pos = pos + 4; + if( length_check(len, pos, 4, handle, identifier) ){ return -1; } + else pos = pos + 4; - hlen = (sig[pos] << 8) | sig[pos + 1]; - pos = pos + hlen + 2; + if( length_check(len, pos, 1, handle, identifier) ){ return -1; } + else hlen = (sig[pos] << 8) | sig[pos + 1]; - ulen = (sig[pos] << 8) | sig[pos + 1]; - pos = pos + 2; + if( length_check(len, pos, 2, handle, identifier) ){ return -1; } + else pos = pos + hlen + 2; + + if( length_check(len, pos, 1, handle, identifier) ){ return -1; } + else ulen = (sig[pos] << 8) | sig[pos + 1]; + + if( length_check(len, pos, 2, handle, identifier) ){ return -1; } + else pos = pos + 2; spos = pos; + if( length_check(len, pos, ulen, handle, identifier) ){ return -1; } + else while(spos < pos + ulen) { if(sig[spos] < 192) { slen = sig[spos]; - spos = spos + 1; + if( length_check(len + ulen, spos, 1, handle, identifier) ){ return -1; } + else spos = spos + 1; } else if(sig[spos] < 255) { - slen = (sig[spos] << 8) | sig[spos + 1]; - spos = spos + 2; + if( length_check(pos + ulen, spos, 1, handle, identifier) ){ return -1; } + else slen = (sig[spos] << 8) | sig[spos + 1]; + if( length_check(pos + ulen, spos, 2, handle, identifier) ){ return -1; } + else spos = spos + 2; } else { - slen = (sig[spos + 1] << 24) | (sig[spos + 2] << 16) | (sig[spos + 3] << 8) | sig[spos + 4]; + if( length_check(len, pos, 4, handle, identifier) ){ return -1; } + else slen = (sig[spos + 1] << 24) | (sig[spos + 2] << 16) | (sig[spos + 3] << 8) | sig[spos + 4]; spos = spos + 5; } @@ -1083,17 +1112,20 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, /* issuer key ID */ char key[17]; size_t i; + if( length_check(pos + ulen, spos, 8, handle, identifier) ){return -1; } + else{ for (i = 0; i < 8; i++) { sprintf(&key[i * 2], "%02X", sig[spos + i + 1]); } + } *keys = alpm_list_add(*keys, strdup(key)); break; } - - spos = spos + slen; + if( length_check(pos + ulen + 1, spos, slen, handle, identifier) ) {return -1; } + else spos = spos + slen; } - - pos = pos + (blen - hlen - 8); + if( length_check( blen, hlen, 8, handle, identifier ) ){return -1;} + else pos = pos + (blen - hlen - 8); } return 0; diff --git a/lib/libalpm/signing.h b/lib/libalpm/signing.h index 3507f584..a67bd900 100644 --- a/lib/libalpm/signing.h +++ b/lib/libalpm/signing.h @@ -36,4 +36,6 @@ int _alpm_key_import(alpm_handle_t *handle, const char *fpr); #endif /* ALPM_SIGNING_H */ +size_t length_check(size_t length, size_t position, size_t a, + alpm_handle_t *handle, const char *identifier); -- GPG fingerprint: '766B 8122 1342 6912 3401 492A 8B54 D7A3 FF3C DB17' Nils Freydank / Holgersson
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