fs: nfs: Fix possible null-pointer dereferences in encode_attrs()

In encode_attrs(), there is an if statement on line 1145 to check
whether label is NULL:
    if (label && (attrmask[2] & FATTR4_WORD2_SECURITY_LABEL))

When label is NULL, it is used on lines 1178-1181:
    *p++ = cpu_to_be32(label->lfs);
    *p++ = cpu_to_be32(label->pi);
    *p++ = cpu_to_be32(label->len);
    p = xdr_encode_opaque_fixed(p, label->label, label->len);

To fix these bugs, label is checked before being used.

These bugs are found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 46a8d63..ab07db0 100644 (file)
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -1174,7 +1174,7 @@ static void encode_attrs(struct xdr_stream *xdr, const struct iattr *iap,
                } else
                        *p++ = cpu_to_be32(NFS4_SET_TO_SERVER_TIME);
        }
-       if (bmval[2] & FATTR4_WORD2_SECURITY_LABEL) {
+       if (label && (bmval[2] & FATTR4_WORD2_SECURITY_LABEL)) {
                *p++ = cpu_to_be32(label->lfs);
                *p++ = cpu_to_be32(label->pi);
                *p++ = cpu_to_be32(label->len);