[PATCH 3.16 091/192] s390/syscalls: Fix out of bounds arguments access

Ben Hutchings
2017-10-09T12:46:44Z

From: Jiri Olsa <jolsa@kernel.org>

commit c46fc0424ced3fb71208e72bd597d91b9169a781 upstream.

Zorro reported following crash while having enabled
syscall tracing (CONFIG_FTRACE_SYSCALLS):

Unable to handle kernel pointer dereference at virtual ...
Oops: 0011 [#1] SMP DEBUG_PAGEALLOC

SNIP

Call Trace:
([<000000000024d79c>] ftrace_syscall_enter+0xec/0x1d8)
[<00000000001099c6>] do_syscall_trace_enter+0x236/0x2f8
[<0000000000730f1c>] sysc_tracesys+0x1a/0x32
[<000003fffcf946a2>] 0x3fffcf946a2
INFO: lockdep is turned off.
Last Breaking-Event-Address:
[<000000000022dd44>] rb_event_data+0x34/0x40
---[ end trace 8c795f86b1b3f7b9 ]---

The crash happens in syscall_get_arguments function for
syscalls with zero arguments, that will try to access
first argument (args[0]) in event entry, but it's not
allocated.

Bail out of there are no arguments.

Reported-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/s390/include/asm/syscall.h | 6 ++++++
1 file changed, 6 insertions(+)

--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h
@@ -64,6 +64,12 @@ static inline void syscall_get_arguments
{
unsigned long mask = -1UL;

+ /*
+ * No arguments for this syscall, there's nothing to do.
+ */
+ if (!n)
+ return;
+
BUG_ON(i + n > 6);
#ifdef CONFIG_COMPAT
if (test_tsk_thread_flag(task, TIF_31BIT))