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[Bug 1794086] Re: readlink(2) returns incorrect size for /proc/self/exe
From: |
Thomas Huth |
Subject: |
[Bug 1794086] Re: readlink(2) returns incorrect size for /proc/self/exe |
Date: |
Wed, 05 May 2021 08:51:04 -0000 |
This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:
https://gitlab.com/qemu-project/qemu/-/issues/154
** Changed in: qemu
Status: New => Expired
** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #154
https://gitlab.com/qemu-project/qemu/-/issues/154
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https://bugs.launchpad.net/bugs/1794086
Title:
readlink(2) returns incorrect size for /proc/self/exe
Status in QEMU:
Expired
Bug description:
readlink(2) seems to ignore the size of supplied buffer for the
resolved name and always returns the actual size of the resolved name
instead.
Steps to reproduce:
```bash
echo '#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, const char** argv)
{
if(argc < 2) exit(1);
char buf[1];
printf("%d\n", readlink(argv[1], buf, sizeof(buf)));
}' >test.c
# I used GCC mipsel cross-compiler to reproduce this bug
mipsel-linux-gnu-gcc-5.5 test.c -o a.out
echo "PWD: `pwd`"
qemu-mipsel ./a.out /proc/self/exe
```
Expected output (observed when running a.out natively on Linux 4.17 amd64):
```
PWD: /tmp/test
1
```
Output observed when running with qemu-mipsel 2.1.2:
```
PWD: /tmp/test
15
```
According to POSIX description of readlink [1], the function shall
return the number of bytes written to the supplied buffer, which
obviously cannot exceed size of the buffer.
Note that the bug is only reproduced with links within /proc
filesystem; links to the regular files within /home are resolved
normally.
The bug is present in qemu-mipsel 2.1.2:
# qemu-mipsel -version
qemu-mipsel version 2.1.2 (Debian 1:2.1+dfsg-12+deb8u6), Copyright (c)
2003-2008 Fabrice Bellard
[1]:
http://pubs.opengroup.org/onlinepubs/009695399/functions/readlink.html
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