RE: [PATCH] IB/hfi1: Fix possible null-pointer dereference in _extend_sdma_tx_descs()

["Marciniszyn, Mike" <mike.marciniszyn@cornelisnetworks.com>]

> Subject: [PATCH] IB/hfi1: Fix possible null-pointer dereference in
> _extend_sdma_tx_descs()
> 
> kmalloc_array() is called to allocate memory for tx->descp. If it fails, the
> function __sdma_txclean() is called:
>   __sdma_txclean(dd, tx);
> 
> However, in the function __sdma_txclean(), tx-descp is dereferenced if
> tx->num_desc is not zero:
>   sdma_unmap_desc(dd, &tx->descp[0]);
> 
> To fix this possible null-pointer dereference, assign 0 to tx->num_desc if
> kmalloc_array() returns NULL.
> 
> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
> Signed-off-by: Tuo Li <islituo@gmail.com>
> ---
>  drivers/infiniband/hw/hfi1/sdma.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/hw/hfi1/sdma.c
> b/drivers/infiniband/hw/hfi1/sdma.c
> index eb15c310d63d..00e29c3dfe96 100644
> --- a/drivers/infiniband/hw/hfi1/sdma.c
> +++ b/drivers/infiniband/hw/hfi1/sdma.c
> @@ -3079,8 +3079,10 @@ static int _extend_sdma_tx_descs(struct
> hfi1_devdata *dd, struct sdma_txreq *tx)
>  			MAX_DESC,
>  			sizeof(struct sdma_desc),
>  			GFP_ATOMIC);
> -	if (!tx->descp)
> +	if (!tx->descp) {
> +		tx->num_desc = 0;
>  		goto enomem;
> +	}
> 
>  	/* reserve last descriptor for coalescing */
>  	tx->desc_limit = MAX_DESC - 1;

Thanks for seeing an issue here, but the correct solution is to store descp locally first.

Once the allocation is shown to be non-NULL, then store to tx-descp:

diff --git a/drivers/infiniband/hw/hfi1/sdma.c b/drivers/infiniband/hw/hfi1/sdma.c
index eb15c310d..b6c554a 100644
--- a/drivers/infiniband/hw/hfi1/sdma.c
+++ b/drivers/infiniband/hw/hfi1/sdma.c
@@ -3055,6 +3055,7 @@ static void __sdma_process_event(struct sdma_engine *sde,
 static int _extend_sdma_tx_descs(struct hfi1_devdata *dd, struct sdma_txreq *tx)
 {
        int i;
+       struct sdma_desc *descp;
 
        /* Handle last descriptor */
        if (unlikely((tx->num_desc == (MAX_DESC - 1)))) {
@@ -3075,12 +3076,12 @@ static int _extend_sdma_tx_descs(struct hfi1_devdata *dd, struct sdma_txreq *tx)
        if (unlikely(tx->num_desc == MAX_DESC))
                goto enomem;
 
-       tx->descp = kmalloc_array(
-                       MAX_DESC,
-                       sizeof(struct sdma_desc),
-                       GFP_ATOMIC);
-       if (!tx->descp)
+       descp = kmalloc_array(MAX_DESC,
+                             sizeof(struct sdma_desc),
+                             GFP_ATOMIC);
+       if (!descp)
                goto enomem;
+       tx->descp = descp;
 
        /* reserve last descriptor for coalescing */
        tx->desc_limit = MAX_DESC - 1;