[PATCH v2] net: 9p: avoid freeing uninit memory in p9pdu_vreadf

[Fedor Pchelkin <pchelkin@ispras.ru>]

If an error occurs while processing an array of strings in p9pdu_vreadf
then uninitialized members of *wnames array are freed.

Fix this by iterating over only lower indices of the array. Also handle
possible uninit *wnames usage if first p9pdu_readf() call inside 'T' case
fails.

Found by Linux Verification Center (linuxtesting.org).

Fixes: ace51c4dd2f9 ("9p: add new protocol support code")
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
---
v2: I've missed that *wnames can also be left uninitialized. Please
ignore the patch v1. As an answer to Dominique's comment: my
organization marks this statement in all commits.

 net/9p/protocol.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index 4e3a2a1ffcb3..043b621f8b84 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -393,6 +393,8 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
 		case 'T':{
 				uint16_t *nwname = va_arg(ap, uint16_t *);
 				char ***wnames = va_arg(ap, char ***);
+				int i;
+				*wnames = NULL;
 
 				errcode = p9pdu_readf(pdu, proto_version,
 								"w", nwname);
@@ -406,8 +408,6 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
 				}
 
 				if (!errcode) {
-					int i;
-
 					for (i = 0; i < *nwname; i++) {
 						errcode =
 						    p9pdu_readf(pdu,
@@ -421,13 +421,11 @@ p9pdu_vreadf(struct p9_fcall *pdu, int proto_version, const char *fmt,
 
 				if (errcode) {
 					if (*wnames) {
-						int i;
-
-						for (i = 0; i < *nwname; i++)
+						while (--i >= 0)
 							kfree((*wnames)[i]);
+						kfree(*wnames);
+						*wnames = NULL;
 					}
-					kfree(*wnames);
-					*wnames = NULL;
 				}
 			}
 			break;
-- 
2.43.0