Re: [PATCH v3] nvme-tcp: fix NULL pointer dereferences in nvmet_tcp_build_pdu_iovec

[Keith Busch <kbusch@kernel.org>]

On Sat, Dec 13, 2025 at 01:57:48PM -0500, Shivam Kumar wrote:
> Commit efa56305908b ("nvmet-tcp: Fix a kernel panic when host sends an invalid H2C PDU length")
> added ttag bounds checking and data_offset
> validation in nvmet_tcp_handle_h2c_data_pdu(), but it did not validate
> whether the command's data structures (cmd->req.sg and cmd->iov) have
> been properly initialized before processing H2C_DATA PDUs.
> 
> The nvmet_tcp_build_pdu_iovec() function dereferences these pointers
> without NULL checks. This can be triggered by sending H2C_DATA PDU
> immediately after the ICREQ/ICRESP handshake, before
> sending a CONNECT command or NVMe write command.
> 
> Attack vectors that trigger NULL pointer dereferences:
> 1. H2C_DATA PDU sent before CONNECT -> both pointers NULL
> 2. H2C_DATA PDU for READ command -> cmd->req.sg allocated, cmd->iov NULL
> 3. H2C_DATA PDU for uninitialized command slot -> both pointers NULL
> 
> The fix validates both cmd->req.sg and cmd->iov before calling
> nvmet_tcp_build_pdu_iovec(). Both checks are required because:
> - Uninitialized commands: both NULL
> - READ commands: cmd->req.sg allocated, cmd->iov NULL
> - WRITE commands: both allocated

Thanks, applied.