[PATCH 5/5] mmc: mxcmmc: fix race conditions for host->req and host->data access

Anatolij Gustschin
2013-03-14T16:41:15Z

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>
---
drivers/mmc/host/mxcmmc.c | 31 ++++++++++++++++++++++++-------
1 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/mmc/host/mxcmmc.c b/drivers/mmc/host/mxcmmc.c
index 48e3fd8..aef6299 100644
--- a/drivers/mmc/host/mxcmmc.c
+++ b/drivers/mmc/host/mxcmmc.c
@@ -736,24 +736,40 @@ 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);
}
}

@@ -1047,7 +1063,8 @@ 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;
--
1.7.5.4