musl - Bug in swab

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Message-ID: <CAB_V0MBDH4MgXunpj67uz7fb1+f2qOS+kTsw0kSJG4P4HF3xLw@mail.gmail.com>
Date: Wed, 28 Dec 2022 17:01:53 +0530
From: Bugs Reporter <bugs@...piler.ai>
To: musl@...ts.openwall.com
Cc: sbansal@...d.ac.in, shubhani@....iitd.ac.in, abhishek.rose@....iitd.ac.in, 
	Jai.Arora.cs518@....iitd.ac.in
Subject: Bug in swab

Hi,

I am writing to report a bug in the swab function of musl.
The bug is in the C implementation of swab as located in the src/string
directory of the musl repository. The musl version was `1.2.3` and the
source code was downloaded from the latest release
<https://musl.libc.org/releases/musl-1.2.3.tar.gz> on the official website.
Please find a detailed report below.

Linux[0] manpage for swab() specifies that the function copies n bytes from
the array pointed to by from to the array pointed to by to, exchanging
adjacent even and odd bytes. This should also work for coinciding memories
and musl's implementation does not take that into account.
An example input is:
    char src[] = {65, 64};
    void* dst = src;
    swab(src, dst, 2);
    if (src[0] != 64 || src[1] != 65) {
      printf("BUG!\n");
    }

The file that demonstrates the bug can be found here
<https://github.com/compilerai/bug-reports/blob/master/bug_files/musl_swab_bug.c>
.
A patch that applies the necessary fix is available here
<https://github.com/compilerai/bug-reports/blob/master/patch/musl_swab.patch>
.

0: https://man7.org/linux/man-pages/man3/swab.3.html

Thanks,

Jai Arora, Abhishek Rose, Shubhani Gupta, Sorav Bansal
CompilerAI Research Group
IIT Delhi, India

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