[Qemu-devel] [PATCH v4] 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.

v4:
- rebased on mainline repo, else condition updated as required.

v3:
- Updated if-else conditions to appropriately handle nwnames = 0.

v2:
- Added check in v9fs_walk_complete as well. 

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

diff --git a/hw/virtio-9p.c b/hw/virtio-9p.c
index 7c59988..1656862 100644
--- a/hw/virtio-9p.c
+++ b/hw/virtio-9p.c
@@ -1482,7 +1482,7 @@ static void v9fs_walk_complete(V9fsState *s, V9fsWalkState *vs, int err)
 {
     complete_pdu(s, vs->pdu, err);
 
-    if (vs->nwnames) {
+    if (vs->nwnames && 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]);
         }
@@ -1578,7 +1578,7 @@ 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 && vs->nwnames <= P9_MAXWELEM) {
         vs->wnames = qemu_mallocz(sizeof(vs->wnames[0]) * vs->nwnames);
 
         vs->qids = qemu_mallocz(sizeof(vs->qids[0]) * vs->nwnames);
@@ -1587,6 +1587,9 @@ static void v9fs_walk(V9fsState *s, V9fsPDU *pdu)
             vs->offset += pdu_unmarshal(vs->pdu, vs->offset, "s",
                                             &vs->wnames[i]);
         }
+    } else if (vs->nwnames > P9_MAXWELEM) {
+        err = -EINVAL;
+        goto out;
     }
 
     vs->fidp = lookup_fid(s, fid);
diff --git a/hw/virtio-9p.h b/hw/virtio-9p.h
index 2ae4ce7..3c92c74 100644
--- a/hw/virtio-9p.h
+++ b/hw/virtio-9p.h
@@ -282,7 +282,7 @@ 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