nfsd: stricter decoding of write-like NFSv2/v3 ops

commit 13bf9fbff0e5e099e2b6f003a0ab8ae145436309 upstream.

The NFSv2/v3 code does not systematically check whether we decode past
the end of the buffer.  This generally appears to be harmless, but there
are a few places where we do arithmetic on the pointers involved and
don't account for the possibility that a length could be negative.  Add
checks to catch these.

Reported-by: Tuomas Haanpää <thaan@synopsys.com>
Reported-by: Ari Kauppi <ari@synopsys.com>
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 6 insertions, 0 deletions

diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index d18cfddbe115..452334694a5d 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -369,6 +369,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
         args->count = ntohl(*p++);
         args->stable = ntohl(*p++);
         len = args->len = ntohl(*p++);
+        if ((void *)p > head->iov_base + head->iov_len)
+                return 0;
         /*
          * The count must equal the amount of data passed.
          */
@@ -472,6 +474,8 @@ nfs3svc_decode_symlinkargs(struct svc_rqst *rqstp, __be32 *p,
         /* first copy and check from the first page */
         old = (char*)p;
         vec = &rqstp->rq_arg.head[0];
+        if ((void *)old > vec->iov_base + vec->iov_len)
+                return 0;
         avail = vec->iov_len - (old - (char*)vec->iov_base);
         while (len && avail && *old) {
                 *new++ = *old++;
diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
index 59bd88a23a3d..de07ff625777 100644
--- a/fs/nfsd/nfsxdr.c
+++ b/fs/nfsd/nfsxdr.c
@@ -302,6 +302,8 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
          * bytes.
          */
         hdr = (void*)p - head->iov_base;
+        if (hdr > head->iov_len)
+                return 0;
         dlen = head->iov_len + rqstp->rq_arg.page_len - hdr;
 
         /*