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Thu, 22 Oct 2026 14:52:37 -0700 (PDT) Received: from ryzen ([2601:644:8000:37f::e34]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ea7b3b01a6sm3090325ad.44.2026.10.22.14.52.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 14:52:37 -0700 (PDT) From: Rosen Penev To: netdev@vger.kernel.org Cc: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= , Broadcom internal kernel review list , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Felix Fietkau , linux-kernel@vger.kernel.org (open list) Subject: [PATCH net v3] net: bgmac: fix TX DMA unmapping and slot cleanup Date: Thu, 22 Oct 2026 14:52:35 -0700 Message-ID: <20261022215235.3692083-1-rosenp@gmail.com> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When mapping a fragment fails, bgmac_dma_tx_add() unwinds with the wrong slots. It passes the failed fragment's slot->dma_addr, which holds the mapping error, to dma_unmap_single() for the head. The fragment loop indexes from ring->end instead of ring->end + 1, so it unmaps the head a second time as a page and leaves the last mapped fragment mapped. None of the affected slots get their dma_addr cleared either, which includes the head slot when mapping the head fails. bgmac_dma_tx_ring_free() unmaps every slot with a non-zero dma_addr, so tearing down the ring unmaps these addresses again. It also frees the skbs of pending TX slots but leaves slot->skb and slot->dma_addr set. The slots survive a down/up cycle, and bgmac_dma_tx_add() only sets slot->skb on the last slot of a packet. If a slot with a stale pointer is later used for the head or a fragment of a scatter/gather packet, bgmac_dma_tx_free() frees the old skb a second time when that slot completes. bgmac_dma_tx_ring_free() also picks dma_unmap_single() or dma_unmap_page() by looking at slot->skb, which is set on the last slot of a packet, while the head was mapped with dma_map_single() and the fragments with skb_frag_dma_map(). In the error path, unmap the head and each mapped fragment from their own slots, and clear dma_addr on every slot the failed packet touched. In bgmac_dma_tx_ring_free(), choose the unmap function by the SOF flag of the descriptor like bgmac_dma_tx_free() does, unmap before freeing, and clear both fields. This was found through code inspection by an LLM while hitting other bugs on an Asus RT-N16. It did not hit these ones specifically. Fixes: 9cde94506eac ("bgmac: implement scatter/gather support") Signed-off-by: Rosen Penev --- v3: clarify how this was found v2: merge two patches into one drivers/net/ethernet/broadcom/bgmac.c | 41 ++++++++++++++++----------- 1 file changed, 24 insertions(+), 17 deletions(-) diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c index e66856337d33..55d126c7d35c 100644 --- a/drivers/net/ethernet/broadcom/bgmac.c +++ b/drivers/net/ethernet/broadcom/bgmac.c @@ -205,19 +205,24 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac, return NETDEV_TX_OK; err_dma: - dma_unmap_single(dma_dev, slot->dma_addr, skb_headlen(skb), - DMA_TO_DEVICE); + slot->dma_addr = 0; while (i-- > 0) { - int index = (ring->end + i) % BGMAC_TX_RING_SLOTS; - struct bgmac_slot_info *slot = &ring->slots[index]; - u32 ctl1 = le32_to_cpu(ring->cpu_base[index].ctl1); - int len = ctl1 & BGMAC_DESC_CTL1_LEN; - - dma_unmap_page(dma_dev, slot->dma_addr, len, DMA_TO_DEVICE); + index = (ring->end + 1 + i) % BGMAC_TX_RING_SLOTS; + slot = &ring->slots[index]; + dma_unmap_page(dma_dev, slot->dma_addr, + skb_frag_size(&skb_shinfo(skb)->frags[i]), + DMA_TO_DEVICE); + slot->dma_addr = 0; } + slot = &ring->slots[ring->end % BGMAC_TX_RING_SLOTS]; + dma_unmap_single(dma_dev, slot->dma_addr, skb_headlen(skb), + DMA_TO_DEVICE); + err_dma_head: + slot->dma_addr = 0; + netdev_err(bgmac->net_dev, "Mapping error of skb on ring 0x%X\n", ring->mmio_base); @@ -535,17 +540,19 @@ static void bgmac_dma_tx_ring_free(struct bgmac *bgmac, unsigned int len = ctl1 & BGMAC_DESC_CTL1_LEN; slot = &ring->slots[i]; - dev_kfree_skb(slot->skb); - if (!slot->dma_addr) - continue; + if (slot->dma_addr) { + if (le32_to_cpu(dma_desc[i].ctl0) & BGMAC_DESC_CTL0_SOF) + dma_unmap_single(dma_dev, slot->dma_addr, + len, DMA_TO_DEVICE); + else + dma_unmap_page(dma_dev, slot->dma_addr, + len, DMA_TO_DEVICE); + slot->dma_addr = 0; + } - if (slot->skb) - dma_unmap_single(dma_dev, slot->dma_addr, - len, DMA_TO_DEVICE); - else - dma_unmap_page(dma_dev, slot->dma_addr, - len, DMA_TO_DEVICE); + dev_kfree_skb(slot->skb); + slot->skb = NULL; } } -- 2.56.0