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Message-ID: <c07133c5-3e2f-c5ed-e2d6-033863ca68c8@gmail.com>
Date: Thu, 4 May 2023 20:53:03 +0200
From: Petr Skocik <pskocik@...il.com>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: Namespace violation in system()?
On 5/4/23 19:52, Rich Felker wrote:
> On Thu, May 04, 2023 at 06:33:27PM +0200, Markus Wichmann wrote:
>> Hi all,
>>
>> I stumbled upon the source code of system() today. It is this at the
>> moment:
>>
>> |int system(const char *cmd)
>> |{
>> | pid_t pid;
>> | sigset_t old, reset;
>> | struct sigaction sa = { .sa_handler = SIG_IGN }, oldint, oldquit;
>> | int status = -1, ret;
>> | posix_spawnattr_t attr;
>> |
>> | pthread_testcancel();
>> |
>> | if (!cmd) return 1;
>> |
>> | sigaction(SIGINT, &sa, &oldint);
>> | sigaction(SIGQUIT, &sa, &oldquit);
>> | sigaddset(&sa.sa_mask, SIGCHLD);
>> | sigprocmask(SIG_BLOCK, &sa.sa_mask, &old);
>> |
>> | sigemptyset(&reset);
>> | if (oldint.sa_handler != SIG_IGN) sigaddset(&reset, SIGINT);
>> | if (oldquit.sa_handler != SIG_IGN) sigaddset(&reset, SIGQUIT);
>> | posix_spawnattr_init(&attr);
>> | posix_spawnattr_setsigmask(&attr, &old);
>> | posix_spawnattr_setsigdefault(&attr, &reset);
>> | posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSIGDEF|POSIX_SPAWN_SETSIGMASK);
>> | ret = posix_spawn(&pid, "/bin/sh", 0, &attr,
>> | (char *[]){"sh", "-c", (char *)cmd, 0}, __environ);
>> | posix_spawnattr_destroy(&attr);
>> |
>> | if (!ret) while (waitpid(pid, &status, 0)<0 && errno == EINTR);
>> | sigaction(SIGINT, &oldint, NULL);
>> | sigaction(SIGQUIT, &oldquit, NULL);
>> | sigprocmask(SIG_SETMASK, &old, NULL);
>> |
>> | if (ret) errno = ret;
>> | return status;
>> |}
>>
>> Aren't all of those calls namespace violations? system() is an ISO-C
>> function, so the only symbols it is allowed to pull into the link are
>> other ISO-C functions or hidden double-underscore symbols, right? But
>> all the functions called here POSIX functions. And while POSIX contains
>> the rule that posix_* functions are reserved, that is in POSIX, not
>> ISO-C. And even with that rule, there are all the other calls.
>>
>> Does someone need to pour out a bucket of underscores over this
>> function?
> The behavior of system() is implementation-defined, so we define it as
> calling those functions. :-)
>
> Rich
Hi. I think Markus Wichmann makes a valid point.
Unless it's valid behavior for
#include <stdio.h>
#include <stdlib.h>
void sigprocmask(void){
puts("Hi, I'm a user-defined sigprocmask");
system("echo hello world");
}
int main(void){ sigprocmask(); }
to keep outputting "Hi, I'm a user-defined sigprocmask" until it crashes
from stack overflow (musl-gcc -static).
Cheers, Petr Skocik
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