misc: fastrpc: fix memory corruption on open

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>
Link: https://lore.kernel.org/r/20220829080531.29681-3-johan+linaro@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 88091778c1b85a670f077ba4fc4190d74d5f9a2c..6e312ac8566866e8cf50e98255e3f872d9a290cb 100644 (file)
--- 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) {