Prevent a possible endless loop with DMAPOOL_DEBUG enabled if a buggy
driver corrupts DMA pool memory.
Signed-off-by: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>
---
Changes since v2:
This is closer to the improved version from "dmapool: reduce footprint
in struct page" in v2 thanks to a previous patch adding blks_per_alloc.
--- linux/mm/dmapool.c.orig 2018-08-06 17:52:53.000000000 -0400
+++ linux/mm/dmapool.c 2018-08-06 17:53:31.000000000 -0400
@@ -454,17 +454,39 @@ void dma_pool_free(struct dma_pool *pool
{
void *page_vaddr = vaddr - offset;
unsigned int chain = page->dma_free_off;
+ unsigned int free_blks = 0;
+
while (chain < pool->allocation) {
- if (chain != offset) {
- chain = *(int *)(page_vaddr + chain);
- continue;
+ if (unlikely(chain == offset)) {
+ spin_unlock_irqrestore(&pool->lock, flags);
+ dev_err(pool->dev,
+ "dma_pool_free %s, dma %pad already free\n",
+ pool->name, &dma);
+ return;
+ }
+
+ /*
+ * A buggy driver could corrupt the freelist by
+ * use-after-free, buffer overflow, etc. Besides
+ * checking for corruption, this also prevents an
+ * endless loop in case corruption causes a circular
+ * loop in the freelist.
+ */
+ if (unlikely(++free_blks + page->dma_in_use >
+ pool->blks_per_alloc)) {
+ freelist_corrupt:
+ spin_unlock_irqrestore(&pool->lock, flags);
+ dev_err(pool->dev,
+ "dma_pool_free %s, freelist corrupted\n",
+ pool->name);
+ return;
}
- spin_unlock_irqrestore(&pool->lock, flags);
- dev_err(pool->dev,
- "dma_pool_free %s, dma %pad already free\n",
- pool->name, &dma);
- return;
+
+ chain = *(int *)(page_vaddr + chain);
}
+ if (unlikely(free_blks + page->dma_in_use !=
+ pool->blks_per_alloc))
+ goto freelist_corrupt;
}
memset(vaddr, POOL_POISON_FREED, pool->size);
#endif
