Subject: Re: [PATCH] staging/rdma/hfi1: Fix a possible null pointer dereference

From: Nicholas Mc Guire <[email-masked]>
Date: Mon, 14 Dec 2015 13:28:49 +0000

On Thu, Dec 10, 2015 at 11:13:38AM -0500, Mike Marciniszyn wrote:
> From: Easwar Hariharan <[email-masked]>
> 
> A code inspection pointed out that kmalloc_array may return NULL and
> memset doesn't check the input pointer for NULL, resulting in a possible
> NULL dereference. This patch fixes this.
> 
> Reviewed-by: Mike Marciniszyn <[email-masked]>
> Signed-off-by: Easwar Hariharan <[email-masked]>
> ---
>  drivers/staging/rdma/hfi1/chip.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/staging/rdma/hfi1/chip.c b/drivers/staging/rdma/hfi1/chip.c
> index dc69159..49d49b2 100644
> --- a/drivers/staging/rdma/hfi1/chip.c
> +++ b/drivers/staging/rdma/hfi1/chip.c
> @@ -10129,6 +10129,8 @@ static void init_qos(struct hfi1_devdata *dd, u32 first_ctxt)
>  	if (num_vls * qpns_per_vl > dd->chip_rcv_contexts)
>  		goto bail;
>  	rsmmap = kmalloc_array(NUM_MAP_REGS, sizeof(u64), GFP_KERNEL);
> +	if (!rsmmap)
> +		goto bail;
>  	memset(rsmmap, rxcontext, NUM_MAP_REGS * sizeof(u64));
>  	/* init the local copy of the table */
>  	for (i = 0, ctxt = first_ctxt; i < num_vls; i++) {
> 
> --

Based on this report a generalization of unchecked use turned up one more
case in the current kernel (patch sent). Probably the  when  block needs 
some cleanup, but findings like this definitely are a case for coccinelle 
scanners.

<snip>
/// check for missing NULL check before use                                     
//
//  missing check in: 
//  ./drivers/staging/rdma/hfi1/chip.c:10131 unchecked allocation
//  in -next-20151214
//  reported-by Mike Marciniszyn <[email-masked]> 
//
//  after generalization this also found:
//  ./drivers/clk/shmobile/clk-div6.c:197 unchecked allocation

virtual context
virtual org
virtual report

@badmemset@
expression mem;
position p;
statement S;
@@

<+...
*mem = kmalloc_array@p(...);
  ... when != if (!mem || ...) S
      when != if (... && !mem) S
      when != if (mem == NULL || ...) S
      when != if (... && mem == NULL) S
      when != if (unlikely(mem == NULL)) S
      when != if (unlikely(!mem)) S
      when != if (likely(!mem)) S
      when != if (likely(mem == NULL)) S
  return;
...+>

@script:python@
p << badmemset.p;
@@

print "%s:%s unchecked allocation" % (p[0].file,p[0].line)

<snip>

thx!
hofrat