From: Hyejeong Choi Date: Fri, 8 Aug 2025 18:05:37 +0000 (+0000) Subject: dma-buf: insert memory barrier before updating num_fences X-Git-Tag: v5.10.241~75 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=90eb79c4ed98a4e24a62ccf61c199ab0f680fa8f;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 [Conflict resolved by applying changes from dma_resv_add_fence() in the original fix to dma_resv_add_shared_fence() in current code base] Signed-off-by: Jay Wang Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 539cb4e043386..72e87380b61a8 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -290,8 +290,9 @@ void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence) replace: RCU_INIT_POINTER(fobj->shared[i], fence); - /* pointer update must be visible before we extend the shared_count */ - smp_store_mb(fobj->shared_count, count); + /* fence update must be visible before we extend the shared_count */ + smp_wmb(); + fobj->shared_count = count; write_seqcount_end(&obj->seq); dma_fence_put(old);