OpenZFS 7263 - deeply nested nvlist can overflow stack

nvlist_pack() and nvlist_unpack are implemented recursively, which can
cause the stack to overflow with a deeply nested nvlist; i.e. an nvlist
which contains an nvlist, which contains an nvlist, which...

Unprivileged users can pass an nvlist to the kernel via certain ioctls
on /dev/zfs, which the kernel will unpack without additional permission
checking or validation. Therefore, an unprivileged user can cause the
kernel's stack to overflow and panic.

Ideally, these functions would be implemented non-recursively. As a
quick fix, this patch limits the depth of the recursion and returns an
error when attempting to pack and unpack a deeply-nested nvlist.

Signed-off-by: Adam Leventhal <[email protected]>
Signed-off-by: George Wilson <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Ported-by: Prakash Surya <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/7263
OpenZFS-commit: openzfs/openzfs@0511d6d

-

module/nvpair/nvpair.c

@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2016 by Delphix. All rights reserved.
  */
 
 #include <sys/stropts.h>
@@ -138,6 +139,11 @@ static int nvlist_add_common(nvlist_t *nvl, const char *name, data_type_t type,
 #define	NVPAIR2I_NVP(nvp) \
 	((i_nvp_t *)((size_t)(nvp) - offsetof(i_nvp_t, nvi_nvp)))
 
+#ifdef _KERNEL
+int nvpair_max_recursion = 20;
+#else
+int nvpair_max_recursion = 100;
+#endif
 
 int
 nv_alloc_init(nv_alloc_t *nva, const nv_alloc_ops_t *nvo, /* args */ ...)
@@ -2017,6 +2023,7 @@ typedef struct {
 	const nvs_ops_t	*nvs_ops;
 	void		*nvs_private;
 	nvpriv_t	*nvs_priv;
+	int		nvs_recursion;
 } nvstream_t;
 
 /*
@@ -2168,9 +2175,16 @@ static int
 nvs_embedded(nvstream_t *nvs, nvlist_t *embedded)
 {
 	switch (nvs->nvs_op) {
-	case NVS_OP_ENCODE:
-		return (nvs_operation(nvs, embedded, NULL));
+	case NVS_OP_ENCODE: {
+		int err;
 
+		if (nvs->nvs_recursion >= nvpair_max_recursion)
+			return (EINVAL);
+		nvs->nvs_recursion++;
+		err = nvs_operation(nvs, embedded, NULL);
+		nvs->nvs_recursion--;
+		return (err);
+	}
 	case NVS_OP_DECODE: {
 		nvpriv_t *priv;
 		int err;
@@ -2183,8 +2197,12 @@ nvs_embedded(nvstream_t *nvs, nvlist_t *embedded)
 
 		nvlist_init(embedded, embedded->nvl_nvflag, priv);
 
+		if (nvs->nvs_recursion >= nvpair_max_recursion)
+			return (EINVAL);
+		nvs->nvs_recursion++;
 		if ((err = nvs_operation(nvs, embedded, NULL)) != 0)
 			nvlist_free(embedded);
+		nvs->nvs_recursion--;
 		return (err);
 	}
 	default:
@@ -2272,6 +2290,7 @@ nvlist_common(nvlist_t *nvl, char *buf, size_t *buflen, int encoding,
 		return (EINVAL);
 
 	nvs.nvs_op = nvs_op;
+	nvs.nvs_recursion = 0;
 
 	/*
 	 * For NVS_OP_ENCODE and NVS_OP_DECODE make sure an nvlist and