[PATCH bpf] x86/kprobes: Fix KRETPROBES when CONFIG_KRETPROBE_ON_RETHOOK is set

From: Adam Zabrocki <pi3@pi3.com.pl>
To: Masami Hiramatsu <mhiramat@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Solar Designer <solar@openwall.com>
Cc: bpf@vger.kernel.org
Subject: [PATCH bpf] x86/kprobes: Fix KRETPROBES when CONFIG_KRETPROBE_ON_RETHOOK is set
Date: Fri, 22 Apr 2022 18:40:27 +0200	[thread overview]
Message-ID: <20220422164027.GA7862@pi3.com.pl> (raw)

[PATCH bpf] x86/kprobes: Fix KRETPROBES when CONFIG_KRETPROBE_ON_RETHOOK is set

The recent kernel change "kprobes: Use rethook for kretprobe if possible",
introduced a potential NULL pointer dereference bug in the KRETPROBE
mechanism. The official Kprobes documentation defines that "Any or all
handlers can be NULL". Unfortunately, there is a missing return handler
verification to fulfill these requirements and can result in a NULL pointer
dereference bug.

This patch adds such verification in kretprobe_rethook_handler() function.

Fixes: 73f9b911faa7 ("kprobes: Use rethook for kretprobe if possible")
Signed-off-by: Adam Zabrocki <pi3@pi3.com.pl>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 kernel/kprobes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index dbe57df2e199..dd58c0be9ce2 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2126,7 +2126,7 @@ static void kretprobe_rethook_handler(struct rethook_node *rh, void *data,
 	struct kprobe_ctlblk *kcb;
 
 	/* The data must NOT be null. This means rethook data structure is broken. */
-	if (WARN_ON_ONCE(!data))
+	if (WARN_ON_ONCE(!data) || !rp->handler)
 		return;
 
 	__this_cpu_write(current_kprobe, &rp->kp);

-- 
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