linux-kernel - [PATCH v2 1/5] HID: intel_ish-hid: fix potential uninitialized data usage

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Date:   Thu, 18 May 2017 22:21:40 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Jiri Kosina <jikos@...nel.org>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnd@...db.de
Subject: [PATCH v2 1/5] HID: intel_ish-hid: fix potential uninitialized data usage

gcc points out an uninialized pointer dereference that could happen
if we ever get to recv_ishtp_cl_msg_dma() or recv_ishtp_cl_msg()
with an empty &dev->read_list:

drivers/hid/intel-ish-hid/ishtp/client.c: In function 'recv_ishtp_cl_msg_dma':
drivers/hid/intel-ish-hid/ishtp/client.c:1049:3: error: 'cl' may be used uninitialized in this function [-Werror=maybe-uninitialized]

The warning only appeared in very few randconfig builds, as the
spinlocks tend to prevent gcc from tracing the variables. I only
saw it in configurations that had neither SMP nor LOCKDEP enabled.

As we can see, we only enter the case if 'complete_rb' is non-NULL,
and then 'cl' is known to point to complete_rb->cl. Adding another
initialization to the same pointer is harmless here and makes it
clear to the compiler that the behavior is well-defined.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/hid/intel-ish-hid/ishtp/client.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hid/intel-ish-hid/ishtp/client.c b/drivers/hid/intel-ish-hid/ishtp/client.c
index aad61328f282..78d393e616a4 100644
--- a/drivers/hid/intel-ish-hid/ishtp/client.c
+++ b/drivers/hid/intel-ish-hid/ishtp/client.c
@@ -925,6 +925,7 @@ void recv_ishtp_cl_msg(struct ishtp_device *dev,
 	}
 
 	if (complete_rb) {
+		cl = complete_rb->cl;
 		getnstimeofday(&cl->ts_rx);
 		++cl->recv_msg_cnt_ipc;
 		ishtp_cl_read_complete(complete_rb);
@@ -1045,6 +1046,7 @@ void recv_ishtp_cl_msg_dma(struct ishtp_device *dev, void *msg,
 	}
 
 	if (complete_rb) {
+		cl = complete_rb->cl;
 		getnstimeofday(&cl->ts_rx);
 		++cl->recv_msg_cnt_dma;
 		ishtp_cl_read_complete(complete_rb);
-- 
2.9.0