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Tue, 21 Jul 2026 21:13:44 -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 v2] xsk: reject undersized tx_metadata at runtime validation Date: Wed, 22 Jul 2026 00:13:26 -0400 Message-ID: <20260722041326.75199-1-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 There is no metadata length check before accessing struct xsk_tx_metadata fields in both xdp_umem_reg() (registration) and xsk_buff_valid_tx_metadata() (runtime). Thus, an invalid small tx_metadata_len (e.g. 8 bytes) passes registration and later causes an out-of-bounds read when xsk_skb_metadata() accesses fields beyond the declared metadata region. 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) Fixing at registration time would break backward compatibility with older userspace applications, so apply a runtime length check in xsk_buff_valid_tx_metadata() that validates tx_metadata_len against the fields required by the enabled flags. Fixes: 341ac980eab9 ("xsk: Support tx_metadata_len") Reported-by: AutonomousCodeSecurity@microsoft.com Link: https://lore.kernel.org/all/20260720155210.34229-1-blbllhy@gmail.com/ Suggested-by: Stanislav Fomichev Signed-off-by: Cen Zhang (Microsoft) --- V2: - Change to runtime per-flag length check as suggested by Stanislav. include/net/xdp_sock_drv.h | 22 ++++++++++++++++++---- net/xdp/xsk.c | 2 +- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/include/net/xdp_sock_drv.h b/include/net/xdp_sock_drv.h index 46797645a0c2..5c54c7462c45 100644 --- a/include/net/xdp_sock_drv.h +++ b/include/net/xdp_sock_drv.h @@ -260,9 +260,22 @@ xsk_buff_raw_get_ctx(const struct xsk_buff_pool *pool, u64 addr) 0) static inline bool -xsk_buff_valid_tx_metadata(const struct xsk_tx_metadata *meta) +xsk_buff_valid_tx_metadata(const struct xsk_buff_pool *pool, + const struct xsk_tx_metadata *meta) { - return !(meta->flags & ~XDP_TXMD_FLAGS_VALID); + /* covers flags, XDP_TXMD_FLAGS_CHECKSUM & XDP_TXMD_FLAGS_TIMESTAMP */ + if (unlikely(pool->tx_metadata_len < 16)) + return false; + + if (unlikely(meta->flags & ~XDP_TXMD_FLAGS_VALID)) + return false; + + if (meta->flags & XDP_TXMD_FLAGS_LAUNCH_TIME) + if (unlikely(pool->tx_metadata_len < + offsetofend(struct xsk_tx_metadata, request.launch_time))) + return false; + + return true; } static inline struct xsk_tx_metadata * @@ -274,7 +287,7 @@ __xsk_buff_get_metadata(const struct xsk_buff_pool *pool, void *data) return NULL; meta = data - pool->tx_metadata_len; - if (unlikely(!xsk_buff_valid_tx_metadata(meta))) + if (unlikely(!xsk_buff_valid_tx_metadata(pool, meta))) return NULL; /* no way to signal the error to the user */ return meta; @@ -469,7 +482,8 @@ xsk_buff_raw_get_ctx(const struct xsk_buff_pool *pool, u64 addr) return (struct xdp_desc_ctx){ }; } -static inline bool xsk_buff_valid_tx_metadata(struct xsk_tx_metadata *meta) +static inline bool xsk_buff_valid_tx_metadata(const struct xsk_buff_pool *pool, + struct xsk_tx_metadata *meta) { return false; } diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index b970f30ea9b9..75b2c97e41e4 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -809,7 +809,7 @@ static int xsk_skb_metadata(struct sk_buff *skb, void *buffer, return -EINVAL; meta = buffer - pool->tx_metadata_len; - if (unlikely(!xsk_buff_valid_tx_metadata(meta))) + if (unlikely(!xsk_buff_valid_tx_metadata(pool, meta))) return -EINVAL; if (meta->flags & XDP_TXMD_FLAGS_CHECKSUM) { -- 2.53.0