CVE-2026-98479: scsi: libiscsi_tcp: Check the data direction of a Data-In PDU

In the Linux kernel, the following vulnerability has been resolved:

scsi: libiscsitcp: Check the data direction of a Data-In PDU

The Data-In branch of iscsitcphdrdissect() resolves the ITT to a task and copies the PDU's data segment into that command's scatterlist without asking whether the command was reading. iscsitcpr2trsp() in the same file does ask, and rejects an R2T for a command that is not DMATODEVICE.

A target that answers a WRITE command's ITT with a Data-In therefore has the initiator write target-supplied bytes into the pages that write was about to send. Those are the caller's own pinned pages for an ODIRECT write, and page cache pages for a buffered one.

Observed against a test target that emits one 512-byte Data-In naming a 128 KB write's ITT, after the R2T for that write. With ODIRECT the caller's buffer ends up holding 512 bytes of the target's data while pwrite() returns 131072. Buffered is quieter: pwrite() and fsync() both succeed, nothing is logged, and reading those blocks back returns the target's bytes out of the page cache without a command going on the wire.

Check the direction before using the scatterlist, the way the R2T path already does.