[PATCH] scsi-generic: fix buffer overflow on block limits inquiry

[Paolo Bonzini]

Using linux 6.x guest, at boot time, an inquiry on a scsi-generic
device makes qemu crash.  This is caused by a buffer overflow when
scsi-generic patches the block limits VPD page.

Do the operations on a temporary on-stack buffer that is guaranteed
to be large enough.

Reported-by: Théo Maillart <tmaillart@freebox.fr>
Analyzed-by: Théo Maillart <tmaillart@freebox.fr>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/scsi/scsi-generic.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index ac9fa662b4e3..373fab0a2a61 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -191,12 +191,15 @@ static int scsi_handle_inquiry_reply(SCSIGenericReq *r, 
SCSIDevice *s, int len)
     if ((s->type == TYPE_DISK || s->type == TYPE_ZBC) &&
         (r->req.cmd.buf[1] & 0x01)) {
         page = r->req.cmd.buf[2];
-        if (page == 0xb0) {
+        if (page == 0xb0 && r->buflen >= 8) {
+            uint8_t buf[16] = {};
             uint64_t max_transfer = calculate_max_transfer(s);
-            stl_be_p(&r->buf[8], max_transfer);
-            /* Also take care of the opt xfer len. */
-            stl_be_p(&r->buf[12],
-                    MIN_NON_ZERO(max_transfer, ldl_be_p(&r->buf[12])));
+
+            memcpy(buf, r->buf, r->buflen);
+            stl_be_p(&buf[8], max_transfer);
+            stl_be_p(&buf[12], MIN_NON_ZERO(max_transfer, ldl_be_p(&buf[12])));
+            memcpy(r->buf + 8, buf + 8, r->buflen - 8);
+
         } else if (s->needs_vpd_bl_emulation && page == 0x00 && r->buflen >= 
4) {
             /*
              * Now we're capable of supplying the VPD Block Limits
-- 
2.40.1