mmc: mxcmmc: fix race conditions for host->req and host->data access

mxcmci_dma_callback() is invoked by DMA drivers in soft-irq
context and can be interrupted by the mxcmci_irq() interrupt
which can finish the mmc request or data transfer and set
host->req or host->data pointers to NULL. Then mxcmci_data_done()
crashes with a null pointer dereferences. Protect all accesses
to host->req and host->data by spin locks.

Also check host->data pointer in mxcmci_watchdog() before
dereferencing it.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 24 insertions, 7 deletions

diff --git a/drivers/mmc/host/mxcmmc.c b/drivers/mmc/host/mxcmmc.c
index 848ab2c2ff05..b82e37af3162 100644
--- a/drivers/mmc/host/mxcmmc.c
+++ b/drivers/mmc/host/mxcmmc.c
@@ -623,24 +623,40 @@ static void mxcmci_datawork(struct work_struct *work)
 
 static void mxcmci_data_done(struct mxcmci_host *host, unsigned int stat)
 {
-        struct mmc_data *data = host->data;
+        struct mmc_request *req;
         int data_error;
+        unsigned long flags;
+
+        spin_lock_irqsave(&host->lock, flags);
 
-        if (!data)
+        if (!host->data) {
+                spin_unlock_irqrestore(&host->lock, flags);
                 return;
+        }
+
+        if (!host->req) {
+                spin_unlock_irqrestore(&host->lock, flags);
+                return;
+        }
+
+        req = host->req;
+        if (!req->stop)
+                host->req = NULL; /* we will handle finish req below */
 
         data_error = mxcmci_finish_data(host, stat);
 
+        spin_unlock_irqrestore(&host->lock, flags);
+
         mxcmci_read_response(host, stat);
         host->cmd = NULL;
 
-        if (host->req->stop) {
-                if (mxcmci_start_cmd(host, host->req->stop, 0)) {
-                        mxcmci_finish_request(host, host->req);
+        if (req->stop) {
+                if (mxcmci_start_cmd(host, req->stop, 0)) {
+                        mxcmci_finish_request(host, req);
                         return;
                 }
         } else {
-                mxcmci_finish_request(host, host->req);
+                mxcmci_finish_request(host, req);
         }
 }
 
@@ -931,7 +947,8 @@ static void mxcmci_watchdog(unsigned long data)
 
         /* Mark transfer as erroneus and inform the upper layers */
 
-        host->data->error = -ETIMEDOUT;
+        if (host->data)
+                host->data->error = -ETIMEDOUT;
         host->req = NULL;
         host->cmd = NULL;
         host->data = NULL;