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 / this is an updated patch.) [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 --- lib/libalpm/signing.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 57 insertions(+), 3 deletions(-) diff --git a/lib/libalpm/signing.c b/lib/libalpm/signing.c index 95cb3280..33438140 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 */ +static 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 @@ -1022,16 +1035,25 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, switch(sig[pos] & 0x03) { case 0: + if(length_check(len, pos, 2, handle, identifier) != 0) { + return -1; + } blen = sig[pos + 1]; pos = pos + 2; break; case 1: + if(length_check(len, pos, 3, handle, identifier)) { + return -1; + } blen = (sig[pos + 1] << 8) | sig[pos + 2]; pos = pos + 3; break; case 2: + if(length_check(len, pos, 5, handle, identifier)) { + return -1; + } blen = (sig[pos + 1] << 24) | (sig[pos + 2] << 16) | (sig[pos + 3] << 8) | sig[pos + 4]; pos = pos + 5; break; @@ -1057,9 +1079,21 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, return -1; } + if(length_check(len, pos, 4, handle, identifier)) { + return -1; + } pos = pos + 4; + /* pos got changed above, so an explicit check is necessary + * check for 2 as that catches another some lines down */ + if(length_check(len, pos, 2, handle, identifier)) { + return -1; + } hlen = (sig[pos] << 8) | sig[pos + 1]; + + if(length_check(len, pos, hlen + 2, handle, identifier)) { + return -1; + } pos = pos + hlen + 2; ulen = (sig[pos] << 8) | sig[pos + 1]; @@ -1067,22 +1101,38 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, spos = pos; + if(length_check(len, pos, ulen, handle, identifier)) { + return -1; + } while(spos < pos + ulen) { if(sig[spos] < 192) { slen = sig[spos]; + if(length_check(len + ulen, spos, 1, handle, identifier)) { + return -1; + } spos = spos + 1; } else if(sig[spos] < 255) { + if(length_check(pos + ulen, spos, 2, handle, identifier)) + { + return -1; + } slen = (sig[spos] << 8) | sig[spos + 1]; spos = spos + 2; } else { + /* check for pos and spos, as spos is still pos */ + if(length_check(len, pos, 5, handle, identifier)) { + return -1; + } slen = (sig[spos + 1] << 24) | (sig[spos + 2] << 16) | (sig[spos + 3] << 8) | sig[spos + 4]; spos = spos + 5; } - if(sig[spos] == 16) { /* issuer key ID */ char key[17]; size_t i; + if(length_check(pos + ulen, spos, 8, handle, identifier)) { + return -1; + } for (i = 0; i < 8; i++) { sprintf(&key[i * 2], "%02X", sig[spos + i + 1]); } @@ -1090,12 +1140,16 @@ int SYMEXPORT alpm_extract_keyid(alpm_handle_t *handle, const char *identifier, break; } + if(length_check(pos + ulen + 1, spos, slen, handle, identifier)) { + return -1; + } spos = spos + slen; } - + if(length_check( blen, hlen, 8, handle, identifier)) { + return -1; + } pos = pos + (blen - hlen - 8); } - return 0; } -- 2.14.1
