This is a defense-in-depth measure in response to bugs like
4d6fa57b4dab ("macsec: avoid heap overflow in skb_to_sgvec"). While
we're at it, we also limit the amount of recursion this function is
allowed to do. Not actually providing a bounded base case is a future
diaster that we can easily avoid here.
Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com>
---
Changes v5->v6:
* Use unlikely() for the rare overflow conditions.
* Also bound recursion, since this is a potential disaster we can avert.
net/core/skbuff.c | 31 ++++++++++++++++++++++++-------
1 file changed, 24 insertions(+), 7 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f86bf69cfb8d..24fb53f8534e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3489,16 +3489,22 @@ void __init skb_init(void)
* @len: Length of buffer space to be mapped
*
* Fill the specified scatter-gather list with mappings/pointers into a
- * region of the buffer space attached to a socket buffer.
+ * region of the buffer space attached to a socket buffer. Returns either
+ * the number of scatterlist items used, or -EMSGSIZE if the contents
+ * could not fit.
*/
static int
-__skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int
len)
+__skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int
len,
+ unsigned int recursion_level)
{
int start = skb_headlen(skb);
int i, copy = start - offset;
struct sk_buff *frag_iter;
int elt = 0;
+ if (unlikely(recursion_level >= 32))
+ return -EMSGSIZE;
+
if (copy > 0) {
if (copy > len)
copy = len;
@@ -3517,6 +3523,8 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist
*sg, int offset, int len)
end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
if ((copy = end - offset) > 0) {
skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ if (unlikely(elt && sg_is_last(&sg[elt - 1])))
+ return -EMSGSIZE;
if (copy > len)
copy = len;
@@ -3531,16 +3539,22 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist
*sg, int offset, int len)
}
skb_walk_frags(skb, frag_iter) {
- int end;
+ int end, ret;
WARN_ON(start > offset + len);
end = start + frag_iter->len;
if ((copy = end - offset) > 0) {
+ if (unlikely(elt && sg_is_last(&sg[elt - 1])))
+ return -EMSGSIZE;
+
if (copy > len)
copy = len;
- elt += __skb_to_sgvec(frag_iter, sg+elt, offset - start,
- copy);
+ ret = __skb_to_sgvec(frag_iter, sg+elt, offset - start,
+ copy, recursion_level + 1);
+ if (unlikely(ret < 0))
+ return ret;
+ elt += ret;
if ((len -= copy) == 0)
return elt;
offset += copy;
@@ -3573,13 +3587,16 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist
*sg, int offset, int len)
int skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
int offset, int len)
{
- return __skb_to_sgvec(skb, sg, offset, len);
+ return __skb_to_sgvec(skb, sg, offset, len, 0);
}
EXPORT_SYMBOL_GPL(skb_to_sgvec_nomark);
int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int
len)
{
- int nsg = __skb_to_sgvec(skb, sg, offset, len);
+ int nsg = __skb_to_sgvec(skb, sg, offset, len, 0);
+
+ if (nsg <= 0)
+ return nsg;
sg_mark_end(&sg[nsg - 1]);
--
2.12.2
