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[128.230.103.233]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5148e7c0fa5sm29137021cf.16.2026.05.08.13.39.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 May 2026 13:39:36 -0700 (PDT) From: Shivam Kumar To: hch@lst.de Cc: mlombard@arkamax.eu, sagi@grimberg.me, kch@nvidia.com, linux-nvme@lists.infradead.org, kbusch@kernel.org, gregkh@linuxfoundation.org, security@kernel.org, Shivam Kumar Subject: [PATCH v3] nvmet-tcp: set and enforce a default MDTS for TCP transport Date: Fri, 8 May 2026 16:39:12 -0400 Message-Id: <20260508203912.320938-1-kumar.shivam43666@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260508_133940_102574_457BD799 X-CRM114-Status: GOOD ( 13.66 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org Unlike other fabrics transports, the TCP target does not set a default Maximum Data Transfer Size. With the configfs MDTS entry defaulting to 0 (no limit), a remote attacker can send a CapsuleCmd with an arbitrarily large SGL length, causing sgl_alloc() in nvmet_tcp_map_data() to attempt an excessive kernel allocation that triggers the OOM killer. Set a default MDTS of 9 (2 MiB) for TCP. Enforce the limit server-side in nvmet_tcp_map_data() by rejecting commands whose SGL length exceeds the configured MDTS, returning NVME_SC_INVALID_FIELD as required by the NVMe specification. Admins can still adjust via the configfs mdts attribute if needed. Signed-off-by: Shivam Kumar --- drivers/nvme/target/tcp.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c index 164a564ba3b4..098cf877c358 100644 --- a/drivers/nvme/target/tcp.c +++ b/drivers/nvme/target/tcp.c @@ -25,6 +25,7 @@ #define NVMET_TCP_DEF_INLINE_DATA_SIZE (4 * PAGE_SIZE) #define NVMET_TCP_MAXH2CDATA 0x400000 /* 16M arbitrary limit */ #define NVMET_TCP_BACKLOG 128 +#define NVMET_TCP_DEF_MDTS 9 /* 2 MiB (2^(12+9)) */ static int param_store_val(const char *str, int *val, int min, int max) { @@ -422,6 +423,13 @@ static int nvmet_tcp_map_data(struct nvmet_tcp_cmd *cmd) if (!len) return 0; + /* Enforce MDTS: abort commands exceeding the advertised limit */ + if (cmd->req.port->mdts) { + u8 mdts = cmd->req.port->mdts; + if (mdts < 20 && len > (1U << (12 + mdts))) + return NVME_SC_INVALID_FIELD | NVME_STATUS_DNR; + } + if (sgl->type == ((NVME_SGL_FMT_DATA_DESC << 4) | NVME_SGL_FMT_OFFSET)) { if (!nvme_is_write(cmd->req.cmd)) @@ -2077,6 +2085,8 @@ static int nvmet_tcp_add_port(struct nvmet_port *nport) INIT_WORK(&port->accept_work, nvmet_tcp_accept_work); if (port->nport->inline_data_size < 0) port->nport->inline_data_size = NVMET_TCP_DEF_INLINE_DATA_SIZE; + if (nport->mdts < 0) + nport->mdts = NVMET_TCP_DEF_MDTS; ret = sock_create(port->addr.ss_family, SOCK_STREAM, IPPROTO_TCP, &port->sock); -- 2.34.1