[tip:x86/urgent] x86/stacktrace: Prevent infinite loop in arch_stack_walk_user()

[tip-bot for Eiichi Tsukata]

Commit-ID:  cbf5b73d162b22e044fe0b7d51dcaa33be065253
Gitweb:     https://git.kernel.org/tip/cbf5b73d162b22e044fe0b7d51dcaa33be065253
Author:     Eiichi Tsukata <de...@etsukata.com>
AuthorDate: Thu, 11 Jul 2019 11:35:01 +0900
Committer:  Thomas Gleixner <t...@linutronix.de>
CommitDate: Thu, 11 Jul 2019 08:22:03 +0200

x86/stacktrace: Prevent infinite loop in arch_stack_walk_user()

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

Once a lack of return address is found, there is no point to continue the
loop, so break out.

Fixes: 02b67518e2b1 ("tracing: add support for userspace stacktraces in 
tracing/iter_ctrl")
Signed-off-by: Eiichi Tsukata <de...@etsukata.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Acked-by: Linus Torvalds <torva...@linux-foundation.org>
Link: https://lkml.kernel.org/r/20190711023501.963-1-de...@etsukata.com

---
 arch/x86/kernel/stacktrace.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 2abf27d7df6b..4f36d3241faf 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -129,11 +129,9 @@ 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)
+                       break;
+               if (!consume_entry(cookie, frame.ret_addr, false))
                        break;
                fp = frame.next_fp;
        }