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

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Date:	Thu,  9 Jun 2016 14:02:04 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Kees Cook <keescook@...omium.org>, Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	user-mode-linux-devel@...ts.sourceforge.net,
	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>,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.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>,
	Russell King <linux@...linux.org.uk>,
	Will Deacon <will.deacon@....com>, x86@...nel.org
Subject: [PATCH 14/14] 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@...omium.org>
Cc: Jeff Dike <jdike@...toit.com>
Cc: Richard Weinberger <richard@....at>
Cc: user-mode-linux-devel@...ts.sourceforge.net
---
 arch/um/kernel/skas/syscall.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

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);
 }
-- 
2.7.4