linux-kernel - [PATCH] seccomp: Only dump core when single-threaded

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Message-ID: <20170207231851.GA129818@beast>
Date:   Tue, 7 Feb 2017 15:18:51 -0800
From:   Kees Cook <keescook@...omium.org>
To:     James Morris <james.l.morris@...cle.com>
Cc:     Mike Frysinger <vapier@...too.org>,
        Paul Moore <paul@...l-moore.com>,
        Tyler Hicks <tyhicks@...onical.com>,
        Andrei Vagin <avagin@...tuozzo.com>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] 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@...omium.org>
---
 kernel/seccomp.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index f8f88ebcb3ba..e15185c28de5 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);
 	}
 	}
-- 
2.7.4


-- 
Kees Cook
Pixel Security