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From: "dpmendenhall at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug string/25933] New: Off by one error in __strncmp_avx2 when
 length=VEC_SIZE*4 and strings are at page boundaries can cause a segfault
Date: Wed, 06 May 2020 23:49:56 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D25933

            Bug ID: 25933
           Summary: Off by one error in __strncmp_avx2 when
                    length=3DVEC_SIZE*4 and strings are at page boundaries
                    can cause a segfault
           Product: glibc
           Version: 2.28
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: string
          Assignee: unassigned at sourceware dot org
          Reporter: dpmendenhall at gmail dot com
  Target Milestone: ---

Created attachment 12507
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D12507&action=3Ded=
it
report

When the two strings being compared are at the end of their pages,
__strncmp_avx2 will fall back to a one-byte-at-a-time loop named
"cross_page_loop". This loop is incorrect if the length of the comparison
exactly matches VEC_SIZE*4, which is 128 on my machine.

Full report in attached pdf.

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