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([187.13.30.172]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-33e96f47d52sm8022700eec.28.2026.09.23.09.23.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 09:23:49 -0700 (PDT) From: Aldo Ariel Panzardo To: maxime.chevallier@bootlin.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, sashiko-bot@kernel.org, Aldo Ariel Panzardo Subject: [PATCH] net: stmmac: guard FCS stripping against runt frames Date: Wed, 23 Sep 2026 13:23:39 -0300 Message-ID: <20260923162339.1375698-1-qwe.aldo@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: 8bit stmmac_rx_zc() and stmmac_rx() strip the 4-byte FCS from the last buffer when ACS (Automatic Checksum Stripping) is disabled: buf1_len -= ETH_FCS_LEN; len -= ETH_FCS_LEN; Neither path checks that the buffer actually contains at least ETH_FCS_LEN bytes. A runt frame delivered by the hardware with a buf1_len or buf2_len smaller than 4 underflows the unsigned subtraction, producing a very large value. In the XDP zero-copy path this wraps data_end backwards: buf->xdp->data_end = buf->xdp->data + buf1_len; giving the XDP/BPF program an enormous data region that extends into adjacent kernel memory. Add the missing lower-bound checks so that undersized frames are silently passed through without stripping. Fixes: bba2556efad6 ("net: stmmac: Enable RX via AF_XDP zero-copy") Cc: stable@vger.kernel.org Reported-by: Sashiko Signed-off-by: Aldo Ariel Panzardo --- diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c index 1fb5f80..4526669 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -5636,7 +5636,8 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue) len += buf1_len; /* ACS is disabled; strip manually. */ - if (likely(!(status & rx_not_ls))) { + if (likely(!(status & rx_not_ls)) && + likely(buf1_len >= ETH_FCS_LEN)) { buf1_len -= ETH_FCS_LEN; len -= ETH_FCS_LEN; } @@ -5808,10 +5809,10 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue) /* ACS is disabled; strip manually. */ if (likely(!(status & rx_not_ls))) { - if (buf2_len) { + if (buf2_len >= ETH_FCS_LEN) { buf2_len -= ETH_FCS_LEN; len -= ETH_FCS_LEN; - } else if (buf1_len) { + } else if (buf1_len >= ETH_FCS_LEN) { buf1_len -= ETH_FCS_LEN; len -= ETH_FCS_LEN; } -- 2.43.0