lienrelatif() reads one byte before its stack buffer on an empty path#729
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The trim that walks back to the last '/' starts at `curr + strlen(curr) - 1`, which is `curr - 1` when the path is empty. The loop then dereferences it. An empty path is reachable today: the pre-pass that strips a query does `strncatbuff(newcurr_fil, curr_fil, a - curr_fil)`, so any `curr_fil` starting with '?' hands the walk an empty string. `-#test=relative "dir/page.html" "?x"` under ASan reports the underflow. The read is one byte and the loop stops immediately either way, so the guard changes no output: over the 484 ordered pairs of a 22-value path corpus, run against builds that force the byte before the buffer to 0 and to '/', the guarded and unguarded results are identical. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Signed-off-by: Xavier Roche <roche@httrack.com>
This was referenced Jul 26, 2026
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lienrelatif()trims its current-path argument back to the last/, starting fromcurr + strlen(curr) - 1. When the path is empty that iscurr - 1, and the loop dereferences it before the bounds test stops it.The empty path is not hypothetical. The pre-pass that strips a query does
strncatbuff(newcurr_fil, curr_fil, a - curr_fil), so anycurr_filbeginning with?hands the trim an empty string.httrack -#test=relative "dir/page.html" "?x"under ASan reports the underflow on current master.The read is a single byte and the loop exits on its
a > currtest whatever that byte holds, so the guard is behaviour-preserving rather than a behaviour change. Checked rather than assumed: 484 ordered pairs from a 22-value path corpus, run against builds that force the byte before the buffer to0and to'/', produce output identical to the guarded build in both states.Found while working on #712, which reaches the same path from a document with no save name.