[PATCH nf] netfilter: nf_tables: replace BUG_ON by element length check

[PATCH nf] netfilter: nf_tables: replace BUG_ON by element length check

[Pablo Neira Ayuso]

BUG_ON can be triggered from userspace with a combination of sufficiently
large extensions. Replace it by length check and return EINVAL instead.

Fixes: 3ac4c07a2400 ("netfilter: nf_tables: add set extensions")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
Extensions have been growing over time, let's replace this BUG_ON by EINVAL.

 include/net/netfilter/nf_tables.h | 14 +++++++----
 net/netfilter/nf_tables_api.c     | 39 +++++++++++++++++++++----------
 2 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 5c4e5a96a984..64cf655c818c 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -657,18 +657,22 @@ static inline void nft_set_ext_prepare(struct nft_set_ext_tmpl *tmpl)
 	tmpl->len = sizeof(struct nft_set_ext);
 }
 
-static inline void nft_set_ext_add_length(struct nft_set_ext_tmpl *tmpl, u8 id,
-					  unsigned int len)
+static inline int nft_set_ext_add_length(struct nft_set_ext_tmpl *tmpl, u8 id,
+					 unsigned int len)
 {
 	tmpl->len	 = ALIGN(tmpl->len, nft_set_ext_types[id].align);
-	BUG_ON(tmpl->len > U8_MAX);
+	if (tmpl->len > U8_MAX)
+		return -EINVAL;
+
 	tmpl->offset[id] = tmpl->len;
 	tmpl->len	+= nft_set_ext_types[id].len + len;
+
+	return 0;
 }
 
-static inline void nft_set_ext_add(struct nft_set_ext_tmpl *tmpl, u8 id)
+static inline int nft_set_ext_add(struct nft_set_ext_tmpl *tmpl, u8 id)
 {
-	nft_set_ext_add_length(tmpl, id, 0);
+	return nft_set_ext_add_length(tmpl, id, 0);
 }
 
 static inline void nft_set_ext_init(struct nft_set_ext *ext,
diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index d6b59beab3a9..2798250ed044 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -5943,7 +5943,9 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 		if (err < 0)
 			goto err_set_elem_expr;
 
-		nft_set_ext_add_length(&tmpl, NFT_SET_EXT_KEY, set->klen);
+		err = nft_set_ext_add_length(&tmpl, NFT_SET_EXT_KEY, set->klen);
+		if (err < 0)
+			goto err_parse_key;
 	}
 
 	if (nla[NFTA_SET_ELEM_KEY_END]) {
@@ -5952,22 +5954,28 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 		if (err < 0)
 			goto err_parse_key;
 
-		nft_set_ext_add_length(&tmpl, NFT_SET_EXT_KEY_END, set->klen);
+		err = nft_set_ext_add_length(&tmpl, NFT_SET_EXT_KEY_END, set->klen);
+		if (err < 0)
+			goto err_parse_key_end;
 	}
 
 	if (timeout > 0) {
 		nft_set_ext_add(&tmpl, NFT_SET_EXT_EXPIRATION);
-		if (timeout != set->timeout)
-			nft_set_ext_add(&tmpl, NFT_SET_EXT_TIMEOUT);
+		if (timeout != set->timeout) {
+			err = nft_set_ext_add(&tmpl, NFT_SET_EXT_TIMEOUT);
+			if (err < 0)
+				goto err_parse_key_end;
+		}
 	}
 
 	if (num_exprs) {
 		for (i = 0; i < num_exprs; i++)
 			size += expr_array[i]->ops->size;
 
-		nft_set_ext_add_length(&tmpl, NFT_SET_EXT_EXPRESSIONS,
-				       sizeof(struct nft_set_elem_expr) +
-				       size);
+		err = nft_set_ext_add_length(&tmpl, NFT_SET_EXT_EXPRESSIONS,
+					     sizeof(struct nft_set_elem_expr) + size);
+		if (err < 0)
+			goto err_parse_key_end;
 	}
 
 	if (nla[NFTA_SET_ELEM_OBJREF] != NULL) {
@@ -5982,7 +5990,9 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 			err = PTR_ERR(obj);
 			goto err_parse_key_end;
 		}
-		nft_set_ext_add(&tmpl, NFT_SET_EXT_OBJREF);
+		err = nft_set_ext_add(&tmpl, NFT_SET_EXT_OBJREF);
+		if (err < 0)
+			goto err_parse_key_end;
 	}
 
 	if (nla[NFTA_SET_ELEM_DATA] != NULL) {
@@ -6016,7 +6026,9 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 							  NFT_VALIDATE_NEED);
 		}
 
-		nft_set_ext_add_length(&tmpl, NFT_SET_EXT_DATA, desc.len);
+		err = nft_set_ext_add_length(&tmpl, NFT_SET_EXT_DATA, desc.len);
+		if (err < 0)
+			goto err_parse_data;
 	}
 
 	/* The full maximum length of userdata can exceed the maximum
@@ -6026,9 +6038,12 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 	ulen = 0;
 	if (nla[NFTA_SET_ELEM_USERDATA] != NULL) {
 		ulen = nla_len(nla[NFTA_SET_ELEM_USERDATA]);
-		if (ulen > 0)
-			nft_set_ext_add_length(&tmpl, NFT_SET_EXT_USERDATA,
-					       ulen);
+		if (ulen > 0) {
+			err = nft_set_ext_add_length(&tmpl, NFT_SET_EXT_USERDATA,
+						     ulen);
+			if (err < 0)
+				goto err_parse_data;
+		}
 	}
 
 	err = -ENOMEM;
-- 
2.30.2