GNU bug report logs - #52481
chown of coreutils may delete the suid of file

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From: Kamil Dudka <kdudka <at> redhat.com>
To: 21625039 <21625039 <at> zju.edu.cn>
Cc: 52481 <at> debbugs.gnu.org
Subject: bug#52481: chown of coreutils may delete the suid of file
Date: Tue, 14 Dec 2021 16:33:00 +0100

On Tuesday, December 14, 2021 3:49:37 AM CET 21625039 wrote:
> I encountered a problem with chown on my fedora34 as the version of
> coreutils is 8.32.
> 
> 
> 
> The reproduce process could see the steps blow:
> 
> [root <at> fedora ~]# ll test.txt
> 
> -rw-r--r--. 1 root root 0 Dec 13 21:13 test.txt
> 
> [root <at> fedora ~]# chmod 4750 test.txt
> 
> [root <at> fedora ~]# ll test.txt
> 
> -rwsr-x---. 1 root root 0 Dec 13 21:13 test.txt
> 
> [root <at> fedora ~]# chown root:root test.txt
> 
> [root <at> fedora ~]# ll test.txt
> 
> -rwxr-x---. 1 root root 0 Dec 13 21:13 test.txt

I believe this is already documented [1]:

    "The chown command sometimes clears the set-user-ID or set-group-ID
    permission bits. This behavior depends on the policy and functionality
    of the underlying chown system call, which may make system-dependent
    file mode modifications outside the control of the chown command."

Kamil

[1] https://www.gnu.org/software/coreutils/manual/html_node/chown-invocation.html

> [root <at> fedora ~]# rpm -qa coreutils
> 
> coreutils-8.32-19.fc34.x86_64
> 
> [root <at> fedora ~]# cat /etc/fedora-release
> 
> Fedora release 34 (Thirty Four)
> 
> 
> 
> Looking forward to hearing from you!
> 
> Thanks.

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