On 11.11.2024 14:47, Prasad Pandit wrote:
On Mon, 11 Nov 2024 at 14:37, Dmitry Frolov <fro...@swemel.ru> wrote:
"int main(int argc, char **argv, char** envp)" is non-standart
Microsoft`s extention of the C language and it`s not portable.
In my particular case (Debian 13, clang-16) this raises wild-pointer
dereference with ASAN message "heap-use-after-free".
...
qos_printf("ENVIRONMENT VARIABLES: {\n");
- for (char **env = envp; *env != 0; env++) {
+ for (char **env = environ; *env != 0; env++) {
qos_printf("\t%s\n", *env);
}
* For heap-use-after-free, there needs to be a free(*env) call
somewhere. In the 'tests/qtest/qos-test.c' file, I couldn't see
environment variables being free'd anywhere. Above loop is only
printing them.
Above loop dereferences the pointer env, which is pointing to
the memory area, which is not allowed to read.
Following small test.c did not reproduce the
'heap-use-after-free' error.
===
#include <stdio.h>
int
main(int argc, char *argv[], char **envp)
{
int n = 0;
for (char **p = envp; *p != 0; p++) {
printf("environ[%d]: %s\n", n++, *p);
}
return 0;
}
$ cc -xc -o test test.c -lasan
===
* While the patch is okay, it is not clear why it fixes the
wild-pointer dereference and "heap-use-after-free" errors.
Thank you.
---
- Prasad
This example will work everywhere, where env pointer is
supported by OS/compiler/etc... Nevertheless, I am pointing on 2 facts:
1. "env" is Microsoft`s extension, not a standard
2. There is exact example, where standards violation raises
undefined behavior: debian13/clang16
