From: Kees Cook <keescook@chromium.org>
Date: Fri, 3 Jun 2016 02:59:42 +0000 (-0700)
Subject: um/ptrace: run seccomp after ptrace
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=26703c636c1f;p=linux-beck.git

um/ptrace: run seccomp after ptrace

Close the hole where ptrace can change a syscall out from under seccomp.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: user-mode-linux-devel@lists.sourceforge.net
---

diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index 9c5570f0f397..ef4b8f949b51 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c
@@ -20,12 +20,12 @@ void handle_syscall(struct uml_pt_regs *r)
 	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
 	PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
 
-	/* Do the secure computing check first; failures should be fast. */
-	if (secure_computing(NULL) == -1)
+	if (syscall_trace_enter(regs))
 		return;
 
-	if (syscall_trace_enter(regs))
-		goto out;
+	/* Do the seccomp check after ptrace; failures should be fast. */
+	if (secure_computing(NULL) == -1)
+		return;
 
 	/* Update the syscall number after orig_ax has potentially been updated
 	 * with ptrace.
@@ -37,6 +37,5 @@ void handle_syscall(struct uml_pt_regs *r)
 		PT_REGS_SET_SYSCALL_RETURN(regs,
 				EXECUTE_SYSCALL(syscall, regs));
 
-out:
 	syscall_trace_leave(regs);
 }