linux-kernel - [PATCH 12/14] powerpc/ptrace: run seccomp after ptrace

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Message-Id: <1465506124-21866-13-git-send-email-keescook@chromium.org>
Date:	Thu,  9 Jun 2016 14:02:02 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Kees Cook <keescook@...omium.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org, Andy Lutomirski <luto@...nel.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-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linux-parisc@...r.kernel.org, linux-s390@...r.kernel.org,
	"Maciej W. Rozycki" <macro@...tec.com>,
	Mark Rutland <mark.rutland@....com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Richard Weinberger <richard@....at>,
	Russell King <linux@...linux.org.uk>,
	user-mode-linux-devel@...ts.sourceforge.net,
	Will Deacon <will.deacon@....com>, x86@...nel.org
Subject: [PATCH 12/14] powerpc/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: Michael Ellerman <mpe@...erman.id.au>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: linuxppc-dev@...ts.ozlabs.org
---
 arch/powerpc/kernel/ptrace.c | 44 +++++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index ed799e994773..5dc47ebb3840 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1788,7 +1788,7 @@ static int do_seccomp(struct pt_regs *regs)
 
 	/*
 	 * The syscall was allowed by seccomp, restore the register
-	 * state to what ptrace and audit expect.
+	 * state to what audit expects.
 	 * Note that we use orig_gpr3, which means a seccomp tracer can
 	 * modify the first syscall parameter (in orig_gpr3) and also
 	 * allow the syscall to proceed.
@@ -1822,22 +1822,25 @@ static inline int do_seccomp(struct pt_regs *regs) { return 0; }
  */
 long do_syscall_trace_enter(struct pt_regs *regs)
 {
-	bool abort = false;
-
 	user_exit();
 
+	/*
+	 * The tracer may decide to abort the syscall, if so tracehook
+	 * will return !0. Note that the tracer may also just change
+	 * regs->gpr[0] to an invalid syscall number, that is handled
+	 * below on the exit path.
+	 */
+	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
+	    tracehook_report_syscall_entry(regs))
+		goto skip;
+
+	/* Run seccomp after ptrace; allow it to set gpr[3]. */
 	if (do_seccomp(regs))
 		return -1;
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE)) {
-		/*
-		 * The tracer may decide to abort the syscall, if so tracehook
-		 * will return !0. Note that the tracer may also just change
-		 * regs->gpr[0] to an invalid syscall number, that is handled
-		 * below on the exit path.
-		 */
-		abort = tracehook_report_syscall_entry(regs) != 0;
-	}
+	/* Avoid trace and audit when syscall is invalid. */
+	if (regs->gpr[0] >= NR_syscalls)
+		goto skip;
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->gpr[0]);
@@ -1854,17 +1857,16 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 				    regs->gpr[5] & 0xffffffff,
 				    regs->gpr[6] & 0xffffffff);
 
-	if (abort || regs->gpr[0] >= NR_syscalls) {
-		/*
-		 * If we are aborting explicitly, or if the syscall number is
-		 * now invalid, set the return value to -ENOSYS.
-		 */
-		regs->gpr[3] = -ENOSYS;
-		return -1;
-	}
-
 	/* Return the possibly modified but valid syscall number */
 	return regs->gpr[0];
+
+skip:
+	/*
+	 * If we are aborting explicitly, or if the syscall number is
+	 * now invalid, set the return value to -ENOSYS.
+	 */
+	regs->gpr[3] = -ENOSYS;
+	return -1;
 }
 
 void do_syscall_trace_leave(struct pt_regs *regs)
-- 
2.7.4