signal/seccomp: Refactor seccomp signal and coredump generation

Factor out force_sig_seccomp from the seccomp signal generation and
place it in kernel/signal.c.  The function force_sig_seccomp takes a
parameter force_coredump to indicate that the sigaction field should
be reset to SIGDFL so that a coredump will be generated when the
signal is delivered.

force_sig_seccomp is then used to replace both seccomp_send_sigsys
and seccomp_init_siginfo.

force_sig_info_to_task gains an extra parameter to force using
the default signal action.

With this change seccomp is no longer a special case and there
becomes exactly one place do_coredump is called from.

Further it no longer becomes necessary for __seccomp_filter
to call do_group_exit.

Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/87r1gr6qc4.fsf_-_@disp2133
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 6 insertions, 34 deletions

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 057e17f3215d..abcbd3d2ba54 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -922,30 +922,6 @@ void get_seccomp_filter(struct task_struct *tsk)
 	refcount_inc(&orig->users);
 }
 
-static void seccomp_init_siginfo(kernel_siginfo_t *info, int syscall, int reason)
-{
-	clear_siginfo(info);
-	info->si_signo = SIGSYS;
-	info->si_code = SYS_SECCOMP;
-	info->si_call_addr = (void __user *)KSTK_EIP(current);
-	info->si_errno = reason;
-	info->si_arch = syscall_get_arch(current);
-	info->si_syscall = syscall;
-}
-
-/**
- * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
- * @syscall: syscall number to send to userland
- * @reason: filter-supplied reason code to send to userland (via si_errno)
- *
- * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
- */
-static void seccomp_send_sigsys(int syscall, int reason)
-{
-	struct kernel_siginfo info;
-	seccomp_init_siginfo(&info, syscall, reason);
-	force_sig_info(&info);
-}
 #endif	/* CONFIG_SECCOMP_FILTER */
 
 /* For use with seccomp_actions_logged */
@@ -1218,7 +1194,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 		/* Show the handler the original registers. */
 		syscall_rollback(current, current_pt_regs());
 		/* Let the filter pass back 16 bits of data. */
-		seccomp_send_sigsys(this_syscall, data);
+		force_sig_seccomp(this_syscall, data, false);
 		goto skip;
 
 	case SECCOMP_RET_TRACE:
@@ -1289,18 +1265,14 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 		/* Dump core only if this is the last remaining thread. */
 		if (action != SECCOMP_RET_KILL_THREAD ||
 		    get_nr_threads(current) == 1) {
-			kernel_siginfo_t info;
-
 			/* Show the original registers in the dump. */
 			syscall_rollback(current, current_pt_regs());
-			/* Trigger a manual coredump since do_exit skips it. */
-			seccomp_init_siginfo(&info, this_syscall, data);
-			do_coredump(&info);
-		}
-		if (action == SECCOMP_RET_KILL_THREAD)
+			/* Trigger a coredump with SIGSYS */
+			force_sig_seccomp(this_syscall, data, true);
+		} else {
 			do_exit(SIGSYS);
-		else
-			do_group_exit(SIGSYS);
+		}
+		return -1; /* skip the syscall go directly to signal handling */
 	}
 
 	unreachable();