"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. */