linux-kernel - Re: [PATCH v2] sparc: make copy

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Date:   Mon, 22 Feb 2021 15:30:22 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     "Dmitry V. Levin" <ldv@...linux.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Anatoly Pugachev <matorola@...il.com>,
        sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sparc: make copy_thread honor pid namespaces

"Dmitry V. Levin" <ldv@...linux.org> writes:

> On sparc, fork and clone syscalls have an unusual semantics of
> returning the pid of the parent process to the child process.
>
> Apparently, the implementation did not honor pid namespaces at all,
> so the child used to get the pid of its parent in the init namespace.
>
> Fortunately, most users of these syscalls are not affected by this bug
> because they use another register to distinguish the parent process
> from its child, and the pid of the parent process is often discarded.
>
> Reproducer:
>
>   $ gcc -Wall -O2 -xc - <<'EOF'
>   #define _GNU_SOURCE
>   #include <err.h>
>   #include <errno.h>
>   #include <sched.h>
>   #include <stdio.h>
>   #include <stdlib.h>
>   #include <sys/wait.h>
>   #include <unistd.h>
>   #include <asm/unistd.h>
>   #include <linux/sched.h>
>   static void test_fork(void)
>   {
>   	int pid = syscall(__NR_fork);
>   	if (pid < 0)
>   		err(1, "fork");
>   	fprintf(stderr, "current: %d, parent: %d, fork returned: %d\n",
>   		getpid(), getppid(), pid);
>   	int status;
>   	if (wait(&status) < 0) {
>   		if (errno == ECHILD)
>   			_exit(0);
>   		err(1, "wait");
>   	}
>   	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
>   		errx(1, "wait: %#x", status);
>   }
>   int main(void)
>   {
>   	test_fork();
>   	if (unshare(CLONE_NEWPID | CLONE_NEWUSER) < 0)
>   		err(1, "unshare");
>   	test_fork();
>   	return 0;
>   }
>   EOF
>   $ sh -c ./a.out
>   current: 10001, parent: 10000, fork returned: 10002
>   current: 10002, parent: 10001, fork returned: 10001
>   current: 10001, parent: 10000, fork returned: 10003
>   current: 1, parent: 0, fork returned: 10001
>
> This bug was found by strace test suite.
>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Dmitry V. Levin <ldv@...linux.org>
> ---
>
> v2: Replaced task_active_pid_ns(p) with current->nsproxy->pid_ns_for_children
>     as suggested by Eric.

I can't test this either.  But from just reading through the code earlier.
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

>  arch/sparc/kernel/process_32.c | 3 ++-
>  arch/sparc/kernel/process_64.c | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/sparc/kernel/process_32.c b/arch/sparc/kernel/process_32.c
> index a02363735915..3be653e40204 100644
> --- a/arch/sparc/kernel/process_32.c
> +++ b/arch/sparc/kernel/process_32.c
> @@ -368,7 +368,8 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
>  #endif
>  
>  	/* Set the return value for the child. */
> -	childregs->u_regs[UREG_I0] = current->pid;
> +	childregs->u_regs[UREG_I0] =
> +		task_pid_nr_ns(current, current->nsproxy->pid_ns_for_children);
>  	childregs->u_regs[UREG_I1] = 1;
>  
>  	/* Set the return value for the parent. */
> diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
> index 6f8c7822fc06..f53ef5cff46a 100644
> --- a/arch/sparc/kernel/process_64.c
> +++ b/arch/sparc/kernel/process_64.c
> @@ -629,7 +629,8 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
>  		t->utraps[0]++;
>  
>  	/* Set the return value for the child. */
> -	t->kregs->u_regs[UREG_I0] = current->pid;
> +	t->kregs->u_regs[UREG_I0] =
> +		task_pid_nr_ns(current, current->nsproxy->pid_ns_for_children);
>  	t->kregs->u_regs[UREG_I1] = 1;
>  
>  	/* Set the second return value for the parent. */