https://bugs.kde.org/show_bug.cgi?id=514094
Bug ID: 514094
Summary: readlink("/proc/self/exe") overwrites buffer beyond
its return value
Classification: Developer tools
Product: valgrind
Version First 3.26.0
Reported In:
Platform: Debian stable
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: ---
SUMMARY
On Debian 13, the following C program behaves differently under valgrind vs not
under valgrind:
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
int main() {
char buf[64];
memset(buf, 0, 64);
int ret = readlink("/proc/self/exe", buf, 64);
printf("ret = %d, buf = %.64s\n", ret, buf);
return 0;
}
STEPS TO REPRODUCE
1. Compile the program: `cc foo.c`
2. Run without valgrind: `./a.out`
3. Run with valgrind: `valgrind ./a.out`
OBSERVED RESULT
Without valgrind: `ret = 17, buf = /home/akuli/a.out`
With valgrind: `ret = 17, buf = /home/akuli/a.outrind/memcheck-amd64-linux`
Return value 17 is correct, but the rest of the buffer is overwritten by the
string `/usr/libexec/valgrind/memcheck-amd64-linux`.
EXPECTED RESULT
Always `ret = 17, buf = /home/akuli/a.out`
SOFTWARE/OS VERSIONS
Debian 13
Valgrind 3.24.0
Valgrind 3.26.0
ADDITIONAL INFORMATION
This is not specific to memcheck: adding `--tool=none` gives me `ret = 17, buf
= /home/akuli/a.outrind/none-amd64-linux`.
I tried with valgrind 3.24.0 from apt and 3.26.0 compiled from source
(valgrind.org), same behavior.
I think this used to work in some version of valgrind, because I got this
problem when valgrinding after I upgraded to a newer Debian.
This only happens with `/proc/self/exe`. If I use another symlink, it works
fine.
`strace ./a.out` gives `readlink("/proc/self/exe", "/home/akuli/a.out", 64)`.
This can be worked around with `buf[ret] = '\0'` or by placing the program to a
directory with a long name.
This is not a compiler problem, because this happens with gcc and with LLVM.
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