[PATCH] x86/stacktrace: Fix infinite loop in arch_stack_walk_user()

[Eiichi Tsukata]

Current arch_stack_walk_user() checks `if (fp == frame.next_fp)`
to prevent infinite loop by self reference but it's not enogh for
circular reference.

Once we find a lack of return address, there is no need to continue
loop, so let's break out.

Fixes: 02b67518e2b1 ("tracing: add support for userspace stacktraces in tracing/iter_ctrl")
Signed-off-by: Eiichi Tsukata <devel@xxxxxxxxxxxx>
---
 arch/x86/kernel/stacktrace.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 2abf27d7df6b..b1a1f4b4c943 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -129,11 +129,8 @@ void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
 			break;
 		if ((unsigned long)fp < regs->sp)
 			break;
-		if (frame.ret_addr) {
-			if (!consume_entry(cookie, frame.ret_addr, false))
-				return;
-		}
-		if (fp == frame.next_fp)
+		if (!frame.ret_addr ||
+		    !consume_entry(cookie, frame.ret_addr, false))
 			break;
 		fp = frame.next_fp;
 	}
-- 
2.21.0