path: root/src/string/memmem.c
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2020-04-30fix undefined behavior from signed overflow in strstr and memmemRich Felker-4/+4
unsigned char promotes to int, which can overflow when shifted left by 24 bits or more. this has been reported multiple times but then forgotten. it's expected to be benign UB, but can trap when built with explicit overflow catching (ubsan or similar). fix it now. note that promotion to uint32_t is safe and portable even outside of the assumptions usually made in musl, since either uint32_t has rank at least unsigned int, so that no further default promotions happen, or int is wide enough that the shift can't overflow. this is a desirable property to have in case someone wants to reuse the code elsewhere.
2018-11-08optimize two-way strstr and memmem bad character shiftRich Felker-1/+1
first, the condition (mem && k < p) is redundant, because mem being nonzero implies the needle is periodic with period exactly p, in which case any byte that appears in the needle must appear in the last p bytes of the needle, bounding the shift (k) by p. second, the whole point of replacing the shift k by mem (=l-p) is to prevent shifting by less than mem when discarding the memory on shift, in which case linear time could not be guaranteed. but as written, the check also replaced shifts greater than mem by mem, reducing the benefit of the shift. there is no possible benefit to this reduction of the shift; since mem is being cleared, the full shift is valid and more optimal. so only replace the shift by mem when it would be less than mem.
2018-11-02fix spuriously slow check in twoway strstr/memmem coresRich Felker-1/+1
mem0 && mem && ... is redundant since mem can only be nonzero when mem0 is nonzero.
2017-09-04fix OOB reads in Xbyte_memmemAlexander Monakov-9/+9
Reported by Leah Neukirchen.
2016-04-01fix read past end of haystack buffer for short needles in memmemRich Felker-0/+1
the two/three/four byte memmem specializations are not prepared to handle haystacks shorter than the needle; they unconditionally read at least up to the needle length and subtract from the haystack length. if the haystack is shorter, the remaining haystack length underflows and produces an unbounded search which will eventually either crash or find a spurious match. the top-level memmem function attempted to avoid this case already by checking for haystack shorter than needle, but it failed to re-check after using memchr to remove the maximal prefix not containing the first byte of the needle.
2014-06-19fix incorrect comparison loop condition in memmemRich Felker-2/+2
the logic for this loop was copied from null-terminated-string logic in strstr without properly adapting it to work with explicit lengths. presumably this error could result in false negatives (wrongly comparing past the end of the needle/haystack), false positives (stopping comparison early when the needle contains null bytes), and crashes (from runaway reads past the end of mapped memory).
2014-04-18fix false negatives with periodic needles in strstr, wcsstr, and memmemRich Felker-1/+1
in cases where the memorized match range from the right factor exceeded the length of the left factor, it was wrongly treated as a mismatch rather than a match. issue reported by Yves Bastide.
2014-04-09fix search past the end of haystack in memmemTimo Teräs-0/+1
to optimize the search, memchr is used to find the first occurrence of the first character of the needle in the haystack before switching to a search for the full needle. however, the number of characters skipped by this first step were not subtracted from the haystack length, causing memmem to search past the end of the haystack.
2013-12-12include cleanups: remove unused headers and add feature test macrosSzabolcs Nagy-1/+0
2012-10-15add memmem function (gnu extension)Rich Felker-0/+148
based on strstr. passes gnulib tests and a few quick checks of my own.