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From: "stephane+sourceware at chazelas dot org"
 <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug glob/31075] New: fnmatch("??") matches on 2-byte single
 characters (as well as 2 any-length characters)
Date: Sat, 18 Nov 2023 10:03:11 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: glibc
X-Bugzilla-Component: glob
X-Bugzilla-Version: 2.34
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: stephane+sourceware at chazelas dot org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31075

            Bug ID: 31075
           Summary: fnmatch("??") matches on 2-byte single characters (as
                    well as 2 any-length characters)
           Product: glibc
           Version: 2.34
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: glob
          Assignee: unassigned at sourceware dot org
          Reporter: stephane+sourceware at chazelas dot org
  Target Milestone: ---

Regression introduced in 2.34 by commit
a79328c745219dcb395070cdcd3be065a8347f24  reproduced on Ubuntu 22.04, Debian
sid libc6:amd64 2.37-12, and current git HEAD
(dae3cf4134d476a4b4ef86fd7012231d6436c15e) built on that sid system.

find . -name '??'

In a UTF-8 locale matches on a UTF-8 encoded =C3=A9=C3=A9 (0xc3 0xa9 0xc3 0=
xa9) but also
on a UTF-8 encoded =C3=A9 (0xc3 0xa9):

To reproduce, from a shell with support for ksh93-style $'...' quotes (ksh9=
3,
zsh, bash...) and on a system where the C.UTF-8 locale has been enabled (ch=
ange
to any other UTF-8 locale if not):

(
  mkdir new-dir && cd new-dir || exit
  touch $'\xc3\xa9' $'\xc3\xa9\xc3\xa9'
  export LC_ALL=3DC.UTF-8
  locale charmap
  find . -name '??'
)

UTF-8
./=C3=A9
./=C3=A9=C3=A9

It seems when fnmatch() fails to match in wchar_t mode, it tries again in c=
har
mode. The pattern is also treated as a char[] array then which makes it even
worth than the (already quite buggy) behaviour of bash pattern matching
(https://lists.gnu.org/archive/html/bug-bash/2021-02/msg00054.html), as tha=
t's
done even when both the subject and pattern are properly encoded in the use=
r's
locale charmap.

$ find . '*[=C3=A1-=C3=A4]*'
./=C3=A9
./=C3=A9=C3=A9

Those didn't match in wchar_t mode but matched in char mode as that became a
*[\303\241-\303\244]* match so matches on anything containing byte 0241 to
0303.

Like for bash, it becomes worse in locales that have characters whose encod=
ing
contains the encoding of [, ] or \ as it can end up matching on a pattern
completely different from the one intended by the user.

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