linux-kernel - [RFC tracing 1/4] tracing: predicate matching trigger crashes for

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Date:   Sun,  7 Aug 2022 23:21:20 +0100
From:   Alan Maguire <alan.maguire@...cle.com>
To:     rostedt@...dmis.org
Cc:     corbet@....net, mingo@...hat.com, shuah@...nel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Alan Maguire <alan.maguire@...cle.com>
Subject: [RFC tracing 1/4] tracing: predicate matching trigger crashes for > 8-byte arrays

The following (wrong) use of tracepoint filtering was enough to trigger
a null-pointer dereference crash:

	cd /sys/kernel/debug/tracing
	echo "saddr_v6 == 0x0100007f" > tcp/tcp_receive_reset/filter
	echo 1 > tcp/tcp_receive_reset/enable
	wget https://localhost

This works fine if saddr - a 4-byte array representing the source address -
is used instead.

Fix is to handle case where we encounter an unexpected size.

Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
---
 kernel/trace/trace_events_filter.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 4b1057ab9d96..65e01c8d48d9 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1490,6 +1490,11 @@ static int parse_pred(const char *str, void *data,
 		else {
 			pred->fn = select_comparison_fn(pred->op, field->size,
 							field->is_signed);
+			if (!pred->fn) {
+				parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP,
+					    pos + i);
+				goto err_free;
+			}
 			if (pred->op == OP_NE)
 				pred->not = 1;
 		}
-- 
2.31.1