"Dmitry V. Levin" <l...@altlinux.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.
>
> This bug was found by strace test suite.
>
> 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>
> int main(void)
> {
> if (unshare(CLONE_NEWPID | CLONE_NEWUSER) < 0)
> err(1, "unshare");
> 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");
> }
> return !WIFEXITED(status) || WEXITSTATUS(status) != 0;
> }
> EOF
> $ sh -c ./a.out
> current: 10001, parent: 10000, fork returned: 10002
> current: 1, parent: 0, fork returned: 10001
>From glibc's sysdeps/unix/sparc/fork.S:
> SYSCALL__ (fork, 0)
> /* %o1 is now 0 for the parent and 1 for the child. Decrement it to
> make it -1 (all bits set) for the parent, and 0 (no bits set)
> for the child. Then AND it with %o0, so the parent gets
> %o0&-1==pid, and the child gets %o0&0==0. */
> sub %o1, 1, %o1
> retl
> and %o0, %o1, %o0
> libc_hidden_def (__fork)
>
> weak_alias (__fork, fork)
This needs to be shared to make the test case make sense.
The change below looks reasonable. Unfortunately because copy_thread
comes before init_task_pid task_active_pid_ns(p) will not work
correctly.
The code below needs to use current->nsproxy->pid_ns_for_children
instead of task_active_pid_ns(p).
For sparc people. Do we know of anyone who actually uses the parent pid
returned from fork to the child process? If not the code can simply
return 0 and we don't have to do this.
Eric
> Cc: Eric W. Biederman <ebied...@xmission.com>
> Cc: sta...@vger.kernel.org
> Signed-off-by: Dmitry V. Levin <l...@altlinux.org>
> ---
>
> Although the fix seems to be obvious, I have no means to test it myself,
> so any help with the testing is much appreciated.
>
> arch/sparc/kernel/process_32.c | 2 +-
> arch/sparc/kernel/process_64.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/sparc/kernel/process_32.c b/arch/sparc/kernel/process_32.c
> index a02363735915..7a89969befa8 100644
> --- a/arch/sparc/kernel/process_32.c
> +++ b/arch/sparc/kernel/process_32.c
> @@ -368,7 +368,7 @@ 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,
> task_active_pid_ns(p));
> 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..ec97217ab970 100644
> --- a/arch/sparc/kernel/process_64.c
> +++ b/arch/sparc/kernel/process_64.c
> @@ -629,7 +629,7 @@ 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,
> task_active_pid_ns(p));
> t->kregs->u_regs[UREG_I1] = 1;
>
> /* Set the second return value for the parent. */
