[Precise][CVE-2014-7826][PATCH 1/2] tracing/syscalls: Fix perf syscall tracing when syscall_nr == -1

[Luis Henriques]

From: Will Deacon <will.deacon at arm.com>

syscall_get_nr can return -1 in the case that the task is not executing
a system call.

This patch fixes perf_syscall_{enter,exit} to check that the syscall
number is valid before using it as an index into a bitmap.

Link: http://lkml.kernel.org/r/1345137254-7377-1-git-send-email-will.deacon@arm.com

Cc: Jason Baron <jbaron at redhat.com>
Cc: Wade Farnsworth <wade_farnsworth at mentor.com>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
(cherry picked from commit 60916a9382e88fbf5e54fd36a3e658efd7ab7bed)
[ luis: prereq for
  086ba77a6db0 "tracing/syscalls: Ignore numbers outside NR_syscalls' range" ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 kernel/trace/trace_syscalls.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 7c75bbb9d541..22a7c9bb31d4 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -519,6 +519,8 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	int size;
 
 	syscall_nr = syscall_get_nr(current, regs);
+	if (syscall_nr < 0)
+		return;
 	if (!test_bit(syscall_nr, enabled_perf_enter_syscalls))
 		return;
 
@@ -593,6 +595,8 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	int size;
 
 	syscall_nr = syscall_get_nr(current, regs);
+	if (syscall_nr < 0)
+		return;
 	if (!test_bit(syscall_nr, enabled_perf_exit_syscalls))
 		return;
 
-- 
2.1.0