[GIT PULL] security: seccomp bugfix

[James Morris]

Please pull this fix for a regression in the seccomp code (it was supposed 
to be in the first pull req but I had it queued in the wrong branch).

The following changes since commit 37c85961c3f87f2141c84e53df31e59db072fd2e:

  Merge tag 'tty-4.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty (2017-02-22 12:17:25 -0800)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git for-linus

Kees Cook (1):
      seccomp: Only dump core when single-threaded

 kernel/seccomp.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

---

commit d7276e321ff8a53106a59c85ca46d03e34288893
Author: Kees Cook <keescook@xxxxxxxxxxxx>
Date:   Tue Feb 7 15:18:51 2017 -0800

    seccomp: Only dump core when single-threaded
    
    The SECCOMP_RET_KILL filter return code has always killed the current
    thread, not the entire process. Changing this as a side-effect of dumping
    core isn't a safe thing to do (a few test suites have already flagged this
    behavioral change). Instead, restore the RET_KILL semantics, but still
    dump core when a RET_KILL delivers SIGSYS to a single-threaded process.
    
    Fixes: b25e67161c29 ("seccomp: dump core when using SECCOMP_RET_KILL")
    Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Acked-by: Andrei Vagin <avagin@xxxxxxxxxxxxx>
    Signed-off-by: James Morris <james.l.morris@xxxxxxxxxx>

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index f8f88eb..e15185c 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -643,11 +643,14 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 	default: {
 		siginfo_t info;
 		audit_seccomp(this_syscall, SIGSYS, action);
-		/* Show the original registers in the dump. */
-		syscall_rollback(current, task_pt_regs(current));
-		/* Trigger a manual coredump since do_exit skips it. */
-		seccomp_init_siginfo(&info, this_syscall, data);
-		do_coredump(&info);
+		/* Dump core only if this is the last remaining thread. */
+		if (get_nr_threads(current) == 1) {
+			/* Show the original registers in the dump. */
+			syscall_rollback(current, task_pt_regs(current));
+			/* Trigger a manual coredump since do_exit skips it. */
+			seccomp_init_siginfo(&info, this_syscall, data);
+			do_coredump(&info);
+		}
 		do_exit(SIGSYS);
 	}
 	}