From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56AB235AC1E for ; Sun, 10 May 2026 13:38:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778420281; cv=none; b=WzF+H/DZw2aCWphTwrGZ+REyaWn25K1T8jRR+zQXZqSezzZyO6+ngoNtgmg8IQLeA20aDkl/4CxA/4KAj8rJCBeo4Pwhhm7/uFTsLA0TNnTIf+S5IjNQEwiUFIADr3OE9UkIvFF8Rdxp5KY+4mAClBOyCePP0acIn4L4xwWWuo0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778420281; c=relaxed/simple; bh=JTo4IJfJcwvhvxz1qXlvlqsw+47RXsTBxadoGXOwjZ8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hsscOtC2O7kBd9gIuYx7WAo1wTjn/T7WKzu8AadmYa4LOviuwyxu5jt2cqqIr/rrvrr1eizVC3Z6cxxm9FfV3pv/NmZ2FHRPqEDWYHFFf971LYHj/646c9MUNxtRtWdMxUWWallTxtu9wdrwhew24qDprmIycwJLIZGSGXrhs1Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TrIyOVsw; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TrIyOVsw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 56F14C2BCF6; Sun, 10 May 2026 13:38:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778420281; bh=JTo4IJfJcwvhvxz1qXlvlqsw+47RXsTBxadoGXOwjZ8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TrIyOVswBhsL/aVvrqeUZr3+zk9scYQK58g2HygkmwPowDcZqlF8zpV7oyH54KRKb tWxZk1TcSeCOZkKnsgMeB+jcK4Qdnf9lAz/FqCOIeUyTFR/+xHu9hub6q0ruaaixJT 1369KGN1Kk0MtLV5dqnZfpoYM0O4zeUOF3KRUS/RMolQQrFwuKSPdbqFmYHLoMCE7g 8A3/J709dMx8Ylo8vj069kNHpuIV1wodViskFxJVED66Ufqyk9aEUgM38zA0QzaPQP FntnJXL+yePKvW6/dWUBb0qbct77hgLasKaYyUNZNPjS54IyAuiXL1iznvVIW2vC5M Bo6ENUl0Wjq2A== From: Sasha Levin To: stable@vger.kernel.org Cc: Sam Edwards , Russell King , Sam Edwards , Paolo Abeni , Sasha Levin Subject: [PATCH 7.0.y 2/2] net: stmmac: Prevent NULL deref when RX memory exhausted Date: Sun, 10 May 2026 09:37:57 -0400 Message-ID: <20260510133757.4137215-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260510133757.4137215-1-sashal@kernel.org> References: <2026050445-outscore-much-bbe7@gregkh> <20260510133757.4137215-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Sam Edwards [ Upstream commit 0bb05e6adfa99a2ea1fee1125cc0953409f83ed8 ] The CPU receives frames from the MAC through conventional DMA: the CPU allocates buffers for the MAC, then the MAC fills them and returns ownership to the CPU. For each hardware RX queue, the CPU and MAC coordinate through a shared ring array of DMA descriptors: one descriptor per DMA buffer. Each descriptor includes the buffer's physical address and a status flag ("OWN") indicating which side owns the buffer: OWN=0 for CPU, OWN=1 for MAC. The CPU is only allowed to set the flag and the MAC is only allowed to clear it, and both must move through the ring in sequence: thus the ring is used for both "submissions" and "completions." In the stmmac driver, stmmac_rx() bookmarks its position in the ring with the `cur_rx` index. The main receive loop in that function checks for rx_descs[cur_rx].own=0, gives the corresponding buffer to the network stack (NULLing the pointer), and increments `cur_rx` modulo the ring size. After the loop exits, stmmac_rx_refill(), which bookmarks its position with `dirty_rx`, allocates fresh buffers and rearms the descriptors (setting OWN=1). If it fails any allocation, it simply stops early (leaving OWN=0) and will retry where it left off when next called. This means descriptors have a three-stage lifecycle (terms my own): - `empty` (OWN=1, buffer valid) - `full` (OWN=0, buffer valid and populated) - `dirty` (OWN=0, buffer NULL) But because stmmac_rx() only checks OWN, it confuses `full`/`dirty`. In the past (see 'Fixes:'), there was a bug where the loop could cycle `cur_rx` all the way back to the first descriptor it dirtied, resulting in a NULL dereference when mistaken for `full`. The aforementioned commit resolved that *specific* failure by capping the loop's iteration limit at `dma_rx_size - 1`, but this is only a partial fix: if the previous stmmac_rx_refill() didn't complete, then there are leftover `dirty` descriptors that the loop might encounter without needing to cycle fully around. The current code therefore panics (see 'Closes:') when stmmac_rx_refill() is memory-starved long enough for `cur_rx` to catch up to `dirty_rx`. Fix this by explicitly checking, before advancing `cur_rx`, if the next entry is dirty; exit the loop if so. This prevents processing of the final, used descriptor until stmmac_rx_refill() succeeds, but fully prevents the `cur_rx == dirty_rx` ambiguity as the previous bugfix intended: so remove the clamp as well. Since stmmac_rx_zc() is a copy-paste-and-tweak of stmmac_rx() and the code structure is identical, any fix to stmmac_rx() will also need a corresponding fix for stmmac_rx_zc(). Therefore, apply the same check there. In stmmac_rx() (not stmmac_rx_zc()), a related bug remains: after the MAC sets OWN=0 on the final descriptor, it will be unable to send any further DMA-complete IRQs until it's given more `empty` descriptors. Currently, the driver simply *hopes* that the next stmmac_rx_refill() succeeds, risking an indefinite stall of the receive process if not. But this is not a regression, so it can be addressed in a future change. Fixes: b6cb4541853c7 ("net: stmmac: avoid rx queue overrun") Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221010 Cc: stable@vger.kernel.org Suggested-by: Russell King Signed-off-by: Sam Edwards Link: https://patch.msgid.link/20260422044503.5349-1-CFSworks@gmail.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- .../net/ethernet/stmicro/stmmac/stmmac_main.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index aa0bf1335ed34..81a6ab19a45bb 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -5469,9 +5469,12 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue) break; /* Prefetch the next RX descriptor */ - rx_q->cur_rx = STMMAC_NEXT_ENTRY(rx_q->cur_rx, - priv->dma_conf.dma_rx_size); - next_entry = rx_q->cur_rx; + next_entry = STMMAC_NEXT_ENTRY(rx_q->cur_rx, + priv->dma_conf.dma_rx_size); + if (unlikely(next_entry == rx_q->dirty_rx)) + break; + + rx_q->cur_rx = next_entry; if (priv->extend_desc) np = (struct dma_desc *)(rx_q->dma_erx + next_entry); @@ -5609,7 +5612,6 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue) dma_dir = page_pool_get_dma_dir(rx_q->page_pool); bufsz = DIV_ROUND_UP(priv->dma_conf.dma_buf_sz, PAGE_SIZE) * PAGE_SIZE; - limit = min(priv->dma_conf.dma_rx_size - 1, (unsigned int)limit); if (netif_msg_rx_status(priv)) { void *rx_head; @@ -5665,9 +5667,12 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue) if (unlikely(status & dma_own)) break; - rx_q->cur_rx = STMMAC_NEXT_ENTRY(rx_q->cur_rx, - priv->dma_conf.dma_rx_size); - next_entry = rx_q->cur_rx; + next_entry = STMMAC_NEXT_ENTRY(rx_q->cur_rx, + priv->dma_conf.dma_rx_size); + if (unlikely(next_entry == rx_q->dirty_rx)) + break; + + rx_q->cur_rx = next_entry; if (priv->extend_desc) np = (struct dma_desc *)(rx_q->dma_erx + next_entry); -- 2.53.0