Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Message-ID: <568967ea-13a7-4a09-6846-0891032e6cfe@cybernetics.com>
Date:   Tue, 7 Jun 2022 14:43:39 -0400
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.1
Subject: [PATCH v6 06/11] dmapool: debug: prevent endless loop in case of
 corruption
Content-Language: en-US
From:   Tony Battersby <tonyb@cybernetics.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     iommu@lists.linux-foundation.org, kernel-team@fb.com,
        Matthew Wilcox <willy@infradead.org>,
        Keith Busch <kbusch@kernel.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Tony Lindgren <tony@atomide.com>
References: <340ff8ef-9ff5-7175-c234-4132bbdfc5f7@cybernetics.com>
In-Reply-To: <340ff8ef-9ff5-7175-c234-4132bbdfc5f7@cybernetics.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

Prevent a possible endless loop with DMAPOOL_DEBUG enabled if a buggy
driver corrupts DMA pool memory.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
---
 mm/dmapool.c | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index d3e5a6151fb4..facdb3571976 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -417,16 +417,39 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 	}
 	{
 		unsigned int chain = page->offset;
+		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,
+					"%s %s, dma %pad already free\n",
+					__func__, pool->name, &dma);
+				return;
 			}
-			spin_unlock_irqrestore(&pool->lock, flags);
-			dev_err(pool->dev, "%s %s, dma %pad already free\n",
-				__func__, 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->in_use >
+				     pool->blks_per_alloc)) {
+ freelist_corrupt:
+				spin_unlock_irqrestore(&pool->lock, flags);
+				dev_err(pool->dev,
+					"%s %s, freelist corrupted\n",
+					__func__, pool->name);
+				return;
+			}
+
+			chain = *(int *)(page->vaddr + chain);
 		}
+		if (unlikely(free_blks + page->in_use !=
+			     pool->blks_per_alloc))
+			goto freelist_corrupt;
 	}
 	memset(vaddr, POOL_POISON_FREED, pool->size);
 #endif
-- 
2.25.1