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Message-ID: <20220721060819.GB9838@prometheus.ethernal.org> Date: Thu, 21 Jul 2022 18:08:19 +1200 From: Mike Beattie <mike@...ernal.org> To: musl@...ts.openwall.com Subject: Bug: BOL/EOL anchors in regex capture groups won't match EOL FRRouting uses musl-libc in its docker container build, and it also appears to be in use in the GNS3 appliances for frr available online. BGP as-path matching is regex powered, and usage of a special token of '_' allows for the easy matching of the boundary of an ASN in an as-path. Internally, it's translated into the regex capture group of: (^|[,{}() ]|$) A valid as-path is a sequence of integers such as: 100 200 300 A BGP as-path filter might be specified as so: bgp as-path access-list foo seq 20 permit _300_ which would get expanded to: (^|[,{}() ]|$)300(^|[,{}() ]|$) when checking for a match. The usage of the pattern "(^|$)" in musl's regex implementation will never match EOL, but it does match BOL. Removal of the circumflex will let the match succeed. Here is the output of a test programs I've written to confirm this: $ musl-gcc -o r r.c $ ./r "_300_" "100 200 300" regex: (^|[,{}() ]|$)300(^|[,{}() ]|$) regexec on [100 200 300]: NOT Found Removal of "^|" from the beginning of the trailing capture group: $ ./r "(^|[,{}() ]|$)300([,{}() ]|$)" "0000 1111 2222" regex: (^|[,{}() ]|$)300([,{}() ]|$) regexec on [100 200 300]: Found Thanks, Mike. -- Mike Beattie <mike@...ernal.org>
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