From: Hyejeong Choi Date: Tue, 13 May 2025 02:06:38 +0000 (-0500) Subject: dma-buf: insert memory barrier before updating num_fences X-Git-Tag: v6.6.92~44 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c9d2b9a80d06a58f37e0dc8c827075639b443927;p=thirdparty%2Fkernel%2Fstable.git dma-buf: insert memory barrier before updating num_fences commit 72c7d62583ebce7baeb61acce6057c361f73be4a upstream. smp_store_mb() inserts memory barrier after storing operation. It is different with what the comment is originally aiming so Null pointer dereference can be happened if memory update is reordered. Signed-off-by: Hyejeong Choi Fixes: a590d0fdbaa5 ("dma-buf: Update reservation shared_count after adding the new fence") CC: stable@vger.kernel.org Reviewed-by: Christian König Link: https://lore.kernel.org/r/20250513020638.GA2329653@au1-maretx-p37.eng.sarc.samsung.com Signed-off-by: Christian König Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index eb8b733065b24..9093f751f1336 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -313,8 +313,9 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence, count++; dma_resv_list_set(fobj, i, fence, usage); - /* pointer update must be visible before we extend the num_fences */ - smp_store_mb(fobj->num_fences, count); + /* fence update must be visible before we extend the num_fences */ + smp_wmb(); + fobj->num_fences = count; } EXPORT_SYMBOL(dma_resv_add_fence);