CVE-2026-89633

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

smb: client: fix OOB read/write from unvalidated DataOffset in coalesce_t2()

coalesce_t2() computes data pointers directly from server-supplied

DataOffset fields with no validation against buffer bounds:

  dataareaof_tgt = (char *)&pSMBt->hdr.Protocol +

                     getunalignedle16(&pSMBt->t2_rsp.DataOffset);

  dataareaof_src = (char *)&pSMBs->hdr.Protocol +

                     getunalignedle16(&pSMBs->t2_rsp.DataOffset);

  dataareaoftgt += totalin_tgt;

  ...

  memcpy(dataareaoftgt, dataareaofsrc, totalinsrc);

A small DataOffset can push a pointer below the actual byte area,

overwriting header fields; a large one can push it past the buffer

end, causing out-of-bounds heap reads (source) or writes (target).

The BCC overflow guard does not prevent this: BCC reflects how much

data is present, while DataOffset controls where in the buffer it

starts.

The "validate target area" comment present since the function was

first written in 2005 was a placeholder that was never implemented.

Add lower- and upper-bound checks for both data pointers before the

memcpy, and before any target header fields are modified.