scsi: ibmvfc: Fix OOB access in ibmvfc_discover_targets_done()

A malicious or compromised VIO server can return a num_written value in the
discover targets MAD response that exceeds max_targets. This value is
stored directly in vhost->num_targets without validation, and is then used
as the loop bound in ibmvfc_alloc_targets() to index into disc_buf[], which
is only allocated for max_targets entries. Indices at or beyond max_targets
access kernel memory outside the DMA-coherent allocation.  The
out-of-bounds data is subsequently embedded in Implicit Logout and PLOGI
MADs that are sent back to the VIO server, leaking kernel memory.

Fix by clamping num_written to max_targets before storing it.

Fixes: 072b91f9c651 ("[SCSI] ibmvfc: IBM Power Virtual Fibre Channel Adapter Client Driver")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Tyllis Xu <LivelyCarpet87@gmail.com>
Reviewed-by: Dave Marquardt <davemarq@linux.ibm.com>
Acked-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Link: https://patch.msgid.link/20260314170151.548614-1-LivelyCarpet87@gmail.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
index a20fce04fe79b6fe177c13470c6d3c4e27d36ddc..3dd2adda195ee22bb3ae543df966fa6da5acd757 100644 (file)
--- a/drivers/scsi/ibmvscsi/ibmvfc.c
+++ b/drivers/scsi/ibmvscsi/ibmvfc.c
@@ -4966,7 +4966,8 @@ static void ibmvfc_discover_targets_done(struct ibmvfc_event *evt)
        switch (mad_status) {
        case IBMVFC_MAD_SUCCESS:
                ibmvfc_dbg(vhost, "Discover Targets succeeded\n");
-               vhost->num_targets = be32_to_cpu(rsp->num_written);
+               vhost->num_targets = min_t(u32, be32_to_cpu(rsp->num_written),
+                                          max_targets);
                ibmvfc_set_host_action(vhost, IBMVFC_HOST_ACTION_ALLOC_TGTS);
                break;
        case IBMVFC_MAD_FAILED: