linux-kernel - [PATCH v2] staging: bcm2835-audio: Fix memory corruption

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Date:   Fri, 11 Aug 2017 11:20:27 +0100
From:   Phil Elwell <phil@...pberrypi.org>
To:     Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Aishwarya Pant <aishpant@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-rpi-kernel@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Cc:     Phil Elwell <phil@...pberrypi.org>
Subject: [PATCH v2] staging: bcm2835-audio: Fix memory corruption

The previous commit (0adbfd46) fixed a memory leak but also freed a
block in the success case, causing a stale pointer to be used with
potentially fatal results. Only free the vchi_instance block in the
case that vchi_connect fails; once connected, the instance is
retained for subsequent connections.

Simplifying the code by removing a bunch of gotos and returning errors
directly.

Signed-off-by: Phil Elwell <phil@...pberrypi.org>
Fixes: 0adbfd4694c2 ("staging: bcm2835-audio: fix memory leak in bcm2835_audio_open_connection()")
---
[Resend with v2 in subject]
v2: Simplified following feedback from Dan Carpenter.
---
 .../vc04_services/bcm2835-audio/bcm2835-vchiq.c       | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
index 5f3d8f2..4be864d 100644
--- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
+++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
@@ -390,8 +390,7 @@ static int bcm2835_audio_open_connection(struct bcm2835_alsa_stream *alsa_stream
 			__func__, instance);
 		instance->alsa_stream = alsa_stream;
 		alsa_stream->instance = instance;
-		ret = 0; // xxx todo -1;
-		goto err_free_mem;
+		return 0;
 	}
 
 	/* Initialize and create a VCHI connection */
@@ -401,16 +400,15 @@ static int bcm2835_audio_open_connection(struct bcm2835_alsa_stream *alsa_stream
 			LOG_ERR("%s: failed to initialise VCHI instance (ret=%d)\n",
 				__func__, ret);
 
-			ret = -EIO;
-			goto err_free_mem;
+			return -EIO;
 		}
 		ret = vchi_connect(NULL, 0, vchi_instance);
 		if (ret) {
 			LOG_ERR("%s: failed to connect VCHI instance (ret=%d)\n",
 				__func__, ret);
 
-			ret = -EIO;
-			goto err_free_mem;
+			kfree(vchi_instance);
+			return -EIO;
 		}
 		initted = 1;
 	}
@@ -421,19 +419,16 @@ static int bcm2835_audio_open_connection(struct bcm2835_alsa_stream *alsa_stream
 	if (IS_ERR(instance)) {
 		LOG_ERR("%s: failed to initialize audio service\n", __func__);
 
-		ret = PTR_ERR(instance);
-		goto err_free_mem;
+		/* vchi_instance is retained for use the next time. */
+		return PTR_ERR(instance);
 	}
 
 	instance->alsa_stream = alsa_stream;
 	alsa_stream->instance = instance;
 
 	LOG_DBG(" success !\n");
-	ret = 0;
-err_free_mem:
-	kfree(vchi_instance);
 
-	return ret;
+	return 0;
 }
 
 int bcm2835_audio_open(struct bcm2835_alsa_stream *alsa_stream)
-- 
1.9.1