linux-kernel - [PATCH 07/14] arm/ptrace: run seccomp after ptrace

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Message-Id: <1465506124-21866-8-git-send-email-keescook@chromium.org>
Date:	Thu,  9 Jun 2016 14:01:57 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Kees Cook <keescook@...omium.org>,
	Russell King <linux@...linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org,
	Andy Lutomirski <luto@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Chris Metcalf <cmetcalf@...lanox.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Helge Deller <deller@....de>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	James Hogan <james.hogan@...tec.com>,
	Jeff Dike <jdike@...toit.com>, linux-arch@...r.kernel.org,
	linux-mips@...ux-mips.org, linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	"Maciej W. Rozycki" <macro@...tec.com>,
	Mark Rutland <mark.rutland@....com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Richard Weinberger <richard@....at>,
	user-mode-linux-devel@...ts.sourceforge.net,
	Will Deacon <will.deacon@....com>, x86@...nel.org
Subject: [PATCH 07/14] arm/ptrace: run seccomp after ptrace

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

Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org
---
 arch/arm/kernel/ptrace.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index ad5e90ab165c..dc7b372872ff 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -932,18 +932,19 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno)
 {
 	current_thread_info()->syscall = scno;
 
-	/* Do the secure computing check first; failures should be fast. */
+	if (test_thread_flag(TIF_SYSCALL_TRACE))
+		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
+
+	/* Do seccomp after ptrace; syscall may have changed. */
 #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
 	if (secure_computing(NULL) == -1)
 		return -1;
 #else
 	/* XXX: remove this once OABI gets fixed */
-	secure_computing_strict(scno);
+	secure_computing_strict(current_thread_info()->syscall);
 #endif
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE))
-		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
-
+	/* Tracer or seccomp may have changed syscall. */
 	scno = current_thread_info()->syscall;
 
 	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
-- 
2.7.4