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From:   Johan Hovold <johan+linaro@kernel.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Amol Maheshwari <amahesh@qti.qualcomm.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Bjorn Andersson <andersson@kernel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Johan Hovold <johan+linaro@kernel.org>, stable@vger.kernel.org
Subject: [PATCH 2/3] misc: fastrpc: fix memory corruption on open
Date:   Mon, 29 Aug 2022 10:05:30 +0200
Message-Id: <20220829080531.29681-3-johan+linaro@kernel.org>
In-Reply-To: <20220829080531.29681-1-johan+linaro@kernel.org>
References: <20220829080531.29681-1-johan+linaro@kernel.org>
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The probe session-duplication overflow check incremented the session
count also when there were no more available sessions so that memory
beyond the fixed-size slab-allocated session array could be corrupted in
fastrpc_session_alloc() on open().

Fixes: f6f9279f2bf0 ("misc: fastrpc: Add Qualcomm fastrpc basic driver model")
Cc: stable@vger.kernel.org      # 5.1
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/misc/fastrpc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 88091778c1b8..6e312ac85668 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1948,7 +1948,7 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 		spin_unlock_irqrestore(&cctx->lock, flags);
 		return -ENOSPC;
 	}
-	sess = &cctx->session[cctx->sesscount];
+	sess = &cctx->session[cctx->sesscount++];
 	sess->used = false;
 	sess->valid = true;
 	sess->dev = dev;
@@ -1961,13 +1961,12 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 		struct fastrpc_session_ctx *dup_sess;
 
 		for (i = 1; i < sessions; i++) {
-			if (cctx->sesscount++ >= FASTRPC_MAX_SESSIONS)
+			if (cctx->sesscount >= FASTRPC_MAX_SESSIONS)
 				break;
-			dup_sess = &cctx->session[cctx->sesscount];
+			dup_sess = &cctx->session[cctx->sesscount++];
 			memcpy(dup_sess, sess, sizeof(*dup_sess));
 		}
 	}
-	cctx->sesscount++;
 	spin_unlock_irqrestore(&cctx->lock, flags);
 	rc = dma_set_mask(dev, DMA_BIT_MASK(32));
 	if (rc) {
-- 
2.35.1