[Qemu-devel] [PATCH v2] v9fs_walk: As per 9p2000 RFC, MAXWELEM >= nwnames >= 0.

[Harsh Prateek Bora <harsh@linux.vnet.ibm.com>]

The nwnames field in TWALK message is assumed to be >=0 and <= MAXWELEM
which is defined as macro P9_MAXWELEM (16) in virtio-9p.h as per 9p2000 RFC.
Appropriate changes are required in V9fsWalkState and v9fs_walk.

v2:
- Added check in v9fs_walk_complete as well.

Signed-off-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
---
 hw/9pfs/virtio-9p.c |    7 +++++--
 hw/9pfs/virtio-9p.h |    2 +-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index 9b44bd0..dde51bc 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -1708,7 +1708,7 @@ static void v9fs_walk_complete(V9fsState *s, V9fsWalkState *vs, int err)
 {
     complete_pdu(s, vs->pdu, err);
 
-    if (vs->nwnames) {
+    if (vs->nwnames <= P9_MAXWELEM) {
         for (vs->name_idx = 0; vs->name_idx < vs->nwnames; vs->name_idx++) {
             v9fs_string_free(&vs->wnames[vs->name_idx]);
         }
@@ -1805,7 +1805,7 @@ static void v9fs_walk(V9fsState *s, V9fsPDU *pdu)
     vs->offset += pdu_unmarshal(vs->pdu, vs->offset, "ddw", &fid,
                                             &newfid, &vs->nwnames);
 
-    if (vs->nwnames) {
+    if (vs->nwnames <= P9_MAXWELEM) {
         vs->wnames = qemu_mallocz(sizeof(vs->wnames[0]) * vs->nwnames);
 
         vs->qids = qemu_mallocz(sizeof(vs->qids[0]) * vs->nwnames);
@@ -1814,6 +1814,9 @@ static void v9fs_walk(V9fsState *s, V9fsPDU *pdu)
             vs->offset += pdu_unmarshal(vs->pdu, vs->offset, "s",
                                             &vs->wnames[i]);
         }
+    } else {
+        err = -EINVAL;
+        goto out;
     }
 
     vs->fidp = lookup_fid(s, fid);
diff --git a/hw/9pfs/virtio-9p.h b/hw/9pfs/virtio-9p.h
index e7d2326..119b12c 100644
--- a/hw/9pfs/virtio-9p.h
+++ b/hw/9pfs/virtio-9p.h
@@ -307,7 +307,7 @@ typedef struct V9fsStatStateDotl {
 typedef struct V9fsWalkState {
     V9fsPDU *pdu;
     size_t offset;
-    int16_t nwnames;
+    uint16_t nwnames;
     int name_idx;
     V9fsQID *qids;
     V9fsFidState *fidp;
-- 
1.7.1.1