NFS: decode_dirent should use an xdr_stream

Convert nfs*xdr.c to use an xdr stream in decode_dirent.  This will prevent a
kernel oops that has been occuring when reading a vmapped page.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 87 insertions, 6 deletions

diff --git a/fs/nfs/nfs3xdr.c b/fs/nfs/nfs3xdr.c
index 52b2fda66e63..d562c8d9d56e 100644
--- a/fs/nfs/nfs3xdr.c
+++ b/fs/nfs/nfs3xdr.c
@@ -100,6 +100,13 @@ static const umode_t nfs_type2fmt[] = {
         [NF3FIFO] = S_IFIFO,
 };
 
+static void print_overflow_msg(const char *func, const struct xdr_stream *xdr)
+{
+        dprintk("nfs: %s: prematurely hit end of receive buffer. "
+                "Remaining buffer length is %tu words.\n",
+                func, xdr->end - xdr->p);
+}
+
 /*
  * Common NFS XDR functions as inlines
  */
@@ -119,6 +126,29 @@ xdr_decode_fhandle(__be32 *p, struct nfs_fh *fh)
         return NULL;
 }
 
+static inline __be32 *
+xdr_decode_fhandle_stream(struct xdr_stream *xdr, struct nfs_fh *fh)
+{
+        __be32 *p;
+        p = xdr_inline_decode(xdr, 4);
+        if (unlikely(!p))
+                goto out_overflow;
+        fh->size = ntohl(*p++);
+
+        if (fh->size <= NFS3_FHSIZE) {
+                p = xdr_inline_decode(xdr, fh->size);
+                if (unlikely(!p))
+                        goto out_overflow;
+                memcpy(fh->data, p, fh->size);
+                return p + XDR_QUADLEN(fh->size);
+        }
+        return NULL;
+
+out_overflow:
+        print_overflow_msg(__func__, xdr);
+        return ERR_PTR(-EIO);
+}
+
 /*
  * Encode/decode time.
  */
@@ -241,6 +271,26 @@ xdr_decode_post_op_attr(__be32 *p, struct nfs_fattr *fattr)
 }
 
 static inline __be32 *
+xdr_decode_post_op_attr_stream(struct xdr_stream *xdr, struct nfs_fattr *fattr)
+{
+        __be32 *p;
+
+        p = xdr_inline_decode(xdr, 4);
+        if (unlikely(!p))
+                goto out_overflow;
+        if (ntohl(*p++)) {
+                p = xdr_inline_decode(xdr, 84);
+                if (unlikely(!p))
+                        goto out_overflow;
+                p = xdr_decode_fattr(p, fattr);
+        }
+        return p;
+out_overflow:
+        print_overflow_msg(__func__, xdr);
+        return ERR_PTR(-EIO);
+}
+
+static inline __be32 *
 xdr_decode_pre_op_attr(__be32 *p, struct nfs_fattr *fattr)
 {
         if (*p++)
@@ -616,19 +666,33 @@ err_unmap:
 }
 
 __be32 *
-nfs3_decode_dirent(__be32 *p, struct nfs_entry *entry, int plus)
+nfs3_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry, int plus)
 {
+        __be32 *p;
         struct nfs_entry old = *entry;
 
-        if (!*p++) {
-                if (!*p)
+        p = xdr_inline_decode(xdr, 4);
+        if (unlikely(!p))
+                goto out_overflow;
+        if (!ntohl(*p++)) {
+                p = xdr_inline_decode(xdr, 4);
+                if (unlikely(!p))
+                        goto out_overflow;
+                if (!ntohl(*p++))
                         return ERR_PTR(-EAGAIN);
                 entry->eof = 1;
                 return ERR_PTR(-EBADCOOKIE);
         }
 
+        p = xdr_inline_decode(xdr, 12);
+        if (unlikely(!p))
+                goto out_overflow;
         p = xdr_decode_hyper(p, &entry->ino);
         entry->len  = ntohl(*p++);
+
+        p = xdr_inline_decode(xdr, entry->len + 8);
+        if (unlikely(!p))
+                goto out_overflow;
         entry->name = (const char *) p;
         p += XDR_QUADLEN(entry->len);
         entry->prev_cookie = entry->cookie;
@@ -636,10 +700,17 @@ nfs3_decode_dirent(__be32 *p, struct nfs_entry *entry, int plus)
 
         if (plus) {
                 entry->fattr->valid = 0;
-                p = xdr_decode_post_op_attr(p, entry->fattr);
+                p = xdr_decode_post_op_attr_stream(xdr, entry->fattr);
+                if (IS_ERR(p))
+                        goto out_overflow_exit;
                 /* In fact, a post_op_fh3: */
+                p = xdr_inline_decode(xdr, 4);
+                if (unlikely(!p))
+                        goto out_overflow;
                 if (*p++) {
-                        p = xdr_decode_fhandle(p, entry->fh);
+                        p = xdr_decode_fhandle_stream(xdr, entry->fh);
+                        if (IS_ERR(p))
+                                goto out_overflow_exit;
                         /* Ugh -- server reply was truncated */
                         if (p == NULL) {
                                 dprintk("NFS: FH truncated\n");
@@ -650,8 +721,18 @@ nfs3_decode_dirent(__be32 *p, struct nfs_entry *entry, int plus)
                         memset((u8*)(entry->fh), 0, sizeof(*entry->fh));
         }
 
-        entry->eof = !p[0] && p[1];
+        p = xdr_inline_peek(xdr, 8);
+        if (p != NULL)
+                entry->eof = !p[0] && p[1];
+        else
+                entry->eof = 0;
+
         return p;
+
+out_overflow:
+        print_overflow_msg(__func__, xdr);
+out_overflow_exit:
+        return ERR_PTR(-EIO);
 }
 
 /*