NFSv4: Fix range checking in __nfs4_get_acl_uncached and __nfs4_proc_set_acl

Ensure that the user supplied buffer size doesn't cause us to overflow
the 'pages' array.

Also fix up some confusion between the use of PAGE_SIZE and
PAGE_CACHE_SIZE when calculating buffer sizes. We're not using
the page cache for anything here.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -3653,11 +3653,11 @@ static inline int nfs4_server_supports_acls(struct nfs_server *server)
 		&& (server->acl_bitmask & ACL4_SUPPORT_DENY_ACL);
 }
 
-/* Assuming that XATTR_SIZE_MAX is a multiple of PAGE_CACHE_SIZE, and that
- * it's OK to put sizeof(void) * (XATTR_SIZE_MAX/PAGE_CACHE_SIZE) bytes on
+/* Assuming that XATTR_SIZE_MAX is a multiple of PAGE_SIZE, and that
+ * it's OK to put sizeof(void) * (XATTR_SIZE_MAX/PAGE_SIZE) bytes on
  * the stack.
  */
-#define NFS4ACL_MAXPAGES (XATTR_SIZE_MAX >> PAGE_CACHE_SHIFT)
+#define NFS4ACL_MAXPAGES DIV_ROUND_UP(XATTR_SIZE_MAX, PAGE_SIZE)
 
 static int buf_to_pages_noslab(const void *buf, size_t buflen,
 		struct page **pages, unsigned int *pgbase)
@@ -3668,7 +3668,7 @@ static int buf_to_pages_noslab(const void *buf, size_t buflen,
 	spages = pages;
 
 	do {
-		len = min_t(size_t, PAGE_CACHE_SIZE, buflen);
+		len = min_t(size_t, PAGE_SIZE, buflen);
 		newpage = alloc_page(GFP_KERNEL);
 
 		if (newpage == NULL)
@@ -3782,17 +3782,16 @@ static ssize_t __nfs4_get_acl_uncached(struct inode *inode, void *buf, size_t bu
 		.rpc_argp = &args,
 		.rpc_resp = &res,
 	};
-	int ret = -ENOMEM, npages, i;
+	unsigned int npages = DIV_ROUND_UP(buflen, PAGE_SIZE);
+	int ret = -ENOMEM, i;
 	size_t acl_len = 0;
 
-	npages = (buflen + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	/* As long as we're doing a round trip to the server anyway,
 	 * let's be prepared for a page of acl data. */
 	if (npages == 0)
 		npages = 1;
-
-	/* Add an extra page to handle the bitmap returned */
-	npages++;
+	if (npages > ARRAY_SIZE(pages))
+		return -ERANGE;
 
 	for (i = 0; i < npages; i++) {
 		pages[i] = alloc_page(GFP_KERNEL);
@@ -3891,10 +3890,13 @@ static int __nfs4_proc_set_acl(struct inode *inode, const void *buf, size_t bufl
 		.rpc_argp	= &arg,
 		.rpc_resp	= &res,
 	};
+	unsigned int npages = DIV_ROUND_UP(buflen, PAGE_SIZE);
 	int ret, i;
 
 	if (!nfs4_server_supports_acls(server))
 		return -EOPNOTSUPP;
+	if (npages > ARRAY_SIZE(pages))
+		return -ERANGE;
 	i = buf_to_pages_noslab(buf, buflen, arg.acl_pages, &arg.acl_pgbase);
 	if (i < 0)
 		return i;