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[24.12.10.127]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8cfc9088df1sm309269185a.25.2026.03.20.21.11.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Mar 2026 21:11:09 -0700 (PDT) From: Tyllis Xu X-Google-Original-From: Tyllis Xu To: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, rmk+kernel@armlinux.org.uk, maxime.chevallier@bootlin.com, peppe.cavallaro@st.com, rayagond@vayavyalabs.com, stable@vger.kernel.org, danisjiang@gmail.com, ychen@northwestern.edu, Tyllis Xu Subject: [PATCH] net: stmmac: fix integer underflow in chain mode jumbo_frm Date: Fri, 20 Mar 2026 23:10:58 -0500 Message-ID: <20260321041058.901149-1-LivelyCarpet87@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The jumbo_frm() chain-mode implementation unconditionally computes len =3D nopaged_len - bmax; where nopaged_len =3D skb_headlen(skb) (linear bytes only) and bmax is BUF_SIZE_8KiB or BUF_SIZE_2KiB. However, the caller stmmac_xmit() decides to invoke jumbo_frm() based on skb->len (total length including page fragments): is_jumbo =3D stmmac_is_jumbo_frm(priv, skb->len, enh_desc); When a packet has a small linear portion (nopaged_len <=3D bmax) but a large total length due to page fragments (skb->len > bmax), the subtraction wraps as an unsigned integer, producing a huge len value (~0xFFFFxxxx). This causes the while (len !=3D 0) loop to execute hundreds of thousands of iterations, passing skb->data + bmax * i pointers far beyond the skb buffer to dma_map_single(). On IOMMU-less SoCs (the typical deployment for stmmac), this maps arbitrary kernel memory to the DMA engine, constituting a kernel memory disclosure and potential memory corruption from hardware. The ring-mode counterpart already guards against this with: if (nopaged_len > BUF_SIZE_8KiB) { ... use len ... } else { ... map nopaged_len directly ... } Apply the same pattern to chain mode: guard the chunked-DMA path with if (nopaged_len > bmax), and add an else branch that maps the entire linear portion as a single descriptor when it fits within bmax. The fragment loop in stmmac_xmit() handles page fragments afterward. Fixes: 286a83721720 ("stmmac: add CHAINED descriptor mode support (V4)") Cc: stable@vger.kernel.org Signed-off-by: Tyllis Xu --- drivers/net/ethernet/stmicro/stmmac/chain_mode.c | 71 ++++++++++++++------= --- 1 file changed, 44 insertions(+), 27 deletions(-) diff --git a/drivers/net/ethernet/stmicro/stmmac/chain_mode.c b/drivers/net= /ethernet/stmicro/stmmac/chain_mode.c index bf351bbec57f..c8980482dea2 100644 --- a/drivers/net/ethernet/stmicro/stmmac/chain_mode.c +++ b/drivers/net/ethernet/stmicro/stmmac/chain_mode.c @@ -31,52 +31,65 @@ static int jumbo_frm(struct stmmac_tx_queue *tx_q, stru= ct sk_buff *skb, else bmax =3D BUF_SIZE_2KiB; - len =3D nopaged_len - bmax; - - des2 =3D dma_map_single(priv->device, skb->data, - bmax, DMA_TO_DEVICE); - desc->des2 =3D cpu_to_le32(des2); - if (dma_mapping_error(priv->device, des2)) - return -1; - tx_q->tx_skbuff_dma[entry].buf =3D des2; - tx_q->tx_skbuff_dma[entry].len =3D bmax; - /* do not close the descriptor and do not set own bit */ - stmmac_prepare_tx_desc(priv, desc, 1, bmax, csum, STMMAC_CHAIN_MODE, - 0, false, skb->len); - - while (len !=3D 0) { - tx_q->tx_skbuff[entry] =3D NULL; - entry =3D STMMAC_GET_ENTRY(entry, priv->dma_conf.dma_tx_size); - desc =3D tx_q->dma_tx + entry; - - if (len > bmax) { - des2 =3D dma_map_single(priv->device, - (skb->data + bmax * i), - bmax, DMA_TO_DEVICE); - desc->des2 =3D cpu_to_le32(des2); - if (dma_mapping_error(priv->device, des2)) - return -1; - tx_q->tx_skbuff_dma[entry].buf =3D des2; - tx_q->tx_skbuff_dma[entry].len =3D bmax; - stmmac_prepare_tx_desc(priv, desc, 0, bmax, csum, - STMMAC_CHAIN_MODE, 1, false, skb->len); - len -=3D bmax; - i++; - } else { - des2 =3D dma_map_single(priv->device, - (skb->data + bmax * i), len, - DMA_TO_DEVICE); - desc->des2 =3D cpu_to_le32(des2); - if (dma_mapping_error(priv->device, des2)) - return -1; - tx_q->tx_skbuff_dma[entry].buf =3D des2; - tx_q->tx_skbuff_dma[entry].len =3D len; - /* last descriptor can be set now */ - stmmac_prepare_tx_desc(priv, desc, 0, len, csum, - STMMAC_CHAIN_MODE, 1, true, skb->len); - len =3D 0; + if (nopaged_len > bmax) { + len =3D nopaged_len - bmax; + + des2 =3D dma_map_single(priv->device, skb->data, + bmax, DMA_TO_DEVICE); + desc->des2 =3D cpu_to_le32(des2); + if (dma_mapping_error(priv->device, des2)) + return -1; + tx_q->tx_skbuff_dma[entry].buf =3D des2; + tx_q->tx_skbuff_dma[entry].len =3D bmax; + /* do not close the descriptor and do not set own bit */ + stmmac_prepare_tx_desc(priv, desc, 1, bmax, csum, STMMAC_CHAIN_MODE, + 0, false, skb->len); + + while (len !=3D 0) { + tx_q->tx_skbuff[entry] =3D NULL; + entry =3D STMMAC_GET_ENTRY(entry, priv->dma_conf.dma_tx_size); + desc =3D tx_q->dma_tx + entry; + + if (len > bmax) { + des2 =3D dma_map_single(priv->device, + (skb->data + bmax * i), + bmax, DMA_TO_DEVICE); + desc->des2 =3D cpu_to_le32(des2); + if (dma_mapping_error(priv->device, des2)) + return -1; + tx_q->tx_skbuff_dma[entry].buf =3D des2; + tx_q->tx_skbuff_dma[entry].len =3D bmax; + stmmac_prepare_tx_desc(priv, desc, 0, bmax, csum, + STMMAC_CHAIN_MODE, 1, false, skb->len); + len -=3D bmax; + i++; + } else { + des2 =3D dma_map_single(priv->device, + (skb->data + bmax * i), len, + DMA_TO_DEVICE); + desc->des2 =3D cpu_to_le32(des2); + if (dma_mapping_error(priv->device, des2)) + return -1; + tx_q->tx_skbuff_dma[entry].buf =3D des2; + tx_q->tx_skbuff_dma[entry].len =3D len; + /* last descriptor can be set now */ + stmmac_prepare_tx_desc(priv, desc, 0, len, csum, + STMMAC_CHAIN_MODE, 1, true, skb->len); + len =3D 0; + } } - } + } else { + des2 =3D dma_map_single(priv->device, skb->data, + nopaged_len, DMA_TO_DEVICE); + desc->des2 =3D cpu_to_le32(des2); + if (dma_mapping_error(priv->device, des2)) + return -1; + tx_q->tx_skbuff_dma[entry].buf =3D des2; + tx_q->tx_skbuff_dma[entry].len =3D nopaged_len; + stmmac_prepare_tx_desc(priv, desc, 1, nopaged_len, csum, + STMMAC_CHAIN_MODE, 0, !skb_is_nonlinear(skb), + skb->len); + } tx_q->cur_tx =3D entry; -- 2.39.5