xen/scsifront: check for a NULL shadow entry on a backend response

scsifront_do_response() validates the rqid in a backend response against
VSCSIIF_MAX_REQS before using it to index info->shadow[], but then
dereferences the entry to test ->inflight without checking that the slot
is populated.  Shadow slots are NULL before a command is submitted (the
host private area is zeroed at allocation) and are reset to NULL in
_scsifront_put_rqid() once a request completes, so an in-range rqid that
does not correspond to an outstanding request makes the frontend
dereference a NULL pointer.

A malicious or buggy backend can thus crash the guest by returning a
response whose rqid is in range but not in flight -- for example a
spurious response before any command has been issued, or a duplicate of
one already completed.  The ring has only VSCSIIF_MAX_REQS (16) slots, so
before the first command every in-range rqid selects a NULL slot.

Reject a response whose shadow slot is not populated.

Fixes: 6d1c2f48f3fc ("xen/scsifront: harden driver against malicious backend")
Cc: stable@vger.kernel.org
Signed-off-by: Yehyeong Lee <yhlee@isslab.korea.ac.kr>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20261005123555.253995-1-yhlee@isslab.korea.ac.kr>

0 files changed, 0 insertions, 0 deletions