[PATCH 1/1] CVE-2022-30767: unbounded memcpy with a failed length check

[gerbert <gerbert@mu-ori.me>]

This patch tries to fix a CVE-2019-14196 fix

   In if-condition, where NFSV2_FLAG is checked, memcpy call is performed
to transfer a reply data of NFS_FHSIZE size. Since the data field in
struct rpc_t structure has the size of (1024 / 4) + 26 = 282, while
NFS_FHSIZE is only 32, it won't lead to out-of-bounds write (considering
the size of data array won't change in the future).

   What concerns if-condition for NFSV3_FLAG, since filefh3_length is
signed integer, it may carry negative values which may lead to memcpy
failure, so in this case we need to introduce not only boundary check
(filefh3_length > NFS3_FHSIZE), which exists, but also make sure that
filefh3_length is not negative.

Signed-off-by: gerbert <gerbert@users.noreply.github.com>
---
  net/nfs.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/nfs.c b/net/nfs.c
index 9152ab742e..5186130ea9 100644
--- a/net/nfs.c
+++ b/net/nfs.c
@@ -566,13 +566,13 @@ static int nfs_lookup_reply(uchar *pkt, unsigned 
len)
  	}

  	if (supported_nfs_versions & NFSV2_FLAG) {
-		if (((uchar *)&(rpc_pkt.u.reply.data[0]) - (uchar *)(&rpc_pkt) + 
NFS_FHSIZE) > len)
-			return -NFS_RPC_DROP;
  		memcpy(filefh, rpc_pkt.u.reply.data + 1, NFS_FHSIZE);
  	} else {  /* NFSV3_FLAG */
  		filefh3_length = ntohl(rpc_pkt.u.reply.data[1]);
+		if (filefh3_length < 0)
+			return -NFS_RPC_DROP;
  		if (filefh3_length > NFS3_FHSIZE)
-			filefh3_length  = NFS3_FHSIZE;
+			filefh3_length = NFS3_FHSIZE;
  		memcpy(filefh, rpc_pkt.u.reply.data + 2, filefh3_length);
  	}

-- 
2.32.0