[PATCH] kprobes: Fix NULL pointer dereference in unregister_kretprobes()

[Luigi Rizzo <lrizzo@google.com>]

In unregister_kretprobes(), rps[i]->rph can be NULL e.g. when called
after kretprobe failed registration. Under !CONFIG_KRETPROBE_ON_RETHOOK,
the unconditional access to rps[i]->rph->rp, causes a kernel panic due
to NULL pointer dereference.

Add a NULL check for rps[i]->rph before invoking rcu_assign_pointer().

Fixes: d839a656d0f3 ("kprobes: consistent rcu api usage for kretprobe holder")
Signed-off-by: Luigi Rizzo <lrizzo@google.com>
---
 kernel/kprobes.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index bfc89083daa93..5dd4786c455de 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2359,7 +2359,8 @@ void unregister_kretprobes(struct kretprobe **rps, int num)
 #ifdef CONFIG_KRETPROBE_ON_RETHOOK
 		rethook_free(rps[i]->rh);
 #else
-		rcu_assign_pointer(rps[i]->rph->rp, NULL);
+		if (rps[i]->rph)
+			rcu_assign_pointer(rps[i]->rph->rp, NULL);
 #endif
 	}
 
-- 
2.48.1.500.g5897711438-goog