ARM: 6884/1: Fix infinite loop in ARM user perf_event backtrace code

The ARM user backtrace code can get into an infinite loop if it
runs into an invalid stack frame which points back to itself.
This situation has been observed in practice.  Fix it by capping
the number of entries in the backtrace.  This is also what other
architectures do in their backtrace code.

Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 979da3947f4272c933739064d576f991c412eeac..139e3c8273696198fa0995a761a5368875961b51 100644 (file)
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -746,7 +746,8 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
 
        tail = (struct frame_tail __user *)regs->ARM_fp - 1;
 
-       while (tail && !((unsigned long)tail & 0x3))
+       while ((entry->nr < PERF_MAX_STACK_DEPTH) &&
+              tail && !((unsigned long)tail & 0x3))
                tail = user_backtrace(tail, entry);
 }