[PATCH] posix: fix false regex match with backrefs and $ anchor

[Carlos O'Donell]

On 4/12/26 3:39 PM, Collin Funk wrote:
> This fixes the $ anchor being ignored in the following grep command:
> 
>      $ grep -E '^(.?)(.?).?\2\1$' <<< ab
>      ab
> 
> However, the regular expression should only match palindromes.
> 
> This patch is mostly copied from a commit in Gnulib from Jim Meyering
> [1]. It was found by Ed Morton in GNU sed [2].
> 
> [1] https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commit;h=8c22765403cc34e87ad953cb3f6901e723c937f5
> [2] https://bugs.gnu.org/68725

May you please file a glibc bug for this so we can track?

Do you think this would have security impact?

-- 
Cheers,
Carlos.