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Mon, 20 Jul 2026 08:52:14 -0700 (PDT) Received: from LAPTOP-83ECOPAB.f7a5e5c3-cab1-4810-bdbb-207cdd06de9e.globalsecureaccess.local ([2001:4898:a800:1012:e4ac:299c:3d12:cc91]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-38e4aff1cd3sm6113063a91.6.2026.07.20.08.52.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jul 2026 08:52:13 -0700 (PDT) From: "Cen Zhang (Microsoft)" To: magnus.karlsson@intel.com, maciej.fijalkowski@intel.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Cc: sdf@fomichev.me, horms@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, tgopinath@linux.microsoft.com, kys@microsoft.com, blbllhy@gmail.com Subject: [PATCH net] xsk: reject tx_metadata_len smaller than struct xsk_tx_metadata Date: Mon, 20 Jul 2026 11:52:10 -0400 Message-ID: <20260720155210.34229-1-blbllhy@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit xdp_umem_reg() validates tx_metadata_len for upper bound (<256) and alignment (%8) but not a lower bound. xsk_skb_metadata() computes meta = buffer - pool->tx_metadata_len then unconditionally accesses the full 24-byte struct xsk_tx_metadata, so any value less than sizeof(struct xsk_tx_metadata) allows an out-of-bounds read. KASAN reports this as: BUG: KASAN: vmalloc-out-of-bounds in xsk_skb_metadata+0x4b2/0x500 Read of size 8 at addr ffffc90000f11000 by task exploit/148 xsk_skb_metadata (net/xdp/xsk.c:837) xsk_build_skb (net/xdp/xsk.c) __xsk_generic_xmit (net/xdp/xsk.c) xsk_sendmsg (net/xdp/xsk.c) Add a lower-bound check in xdp_umem_reg() to reject tx_metadata_len values that cannot cover the full metadata struct. Fixes: 341ac980eab9 ("xsk: Support tx_metadata_len") Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Cen Zhang (Microsoft) --- net/xdp/xdp_umem.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c index 58da2f4f4397..d16ad9d8f919 100644 --- a/net/xdp/xdp_umem.c +++ b/net/xdp/xdp_umem.c @@ -208,7 +208,8 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr) return -EINVAL; if (mr->flags & XDP_UMEM_TX_METADATA_LEN) { - if (mr->tx_metadata_len >= 256 || mr->tx_metadata_len % 8) + if (mr->tx_metadata_len < sizeof(struct xsk_tx_metadata) || + mr->tx_metadata_len >= 256 || mr->tx_metadata_len % 8) return -EINVAL; umem->tx_metadata_len = mr->tx_metadata_len; } -- 2.53.0