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authorJason A. Donenfeld <Jason@zx2c4.com>2017-06-04 04:16:22 +0200
committerDavid S. Miller <davem@davemloft.net>2017-06-04 23:01:47 -0400
commit48a1df65334b74bd7531f932cca5928932abf769 (patch)
treeda1baab25c096414f2af17e97dbec7172426f53d /include/linux
parenta11227dcc345c1792945cae8a3b22882a723620f (diff)
skbuff: return -EMSGSIZE in skb_to_sgvec to prevent overflow
This is a defense-in-depth measure in response to bugs like 4d6fa57b4dab ("macsec: avoid heap overflow in skb_to_sgvec"). There's not only a potential overflow of sglist items, but also a stack overflow potential, so we fix this by limiting the amount of recursion this function is allowed to do. Not actually providing a bounded base case is a future disaster that we can easily avoid here. As a small matter of house keeping, we take this opportunity to move the documentation comment over the actual function the documentation is for. While this could be implemented by using an explicit stack of skbuffs, when implementing this, the function complexity increased considerably, and I don't think such complexity and bloat is actually worth it. So, instead I built this and tested it on x86, x86_64, ARM, ARM64, and MIPS, and measured the stack usage there. I also reverted the recent MIPS changes that give it a separate IRQ stack, so that I could experience some worst-case situations. I found that limiting it to 24 layers deep yielded a good stack usage with room for safety, as well as being much deeper than any driver actually ever creates. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Cc: Steffen Klassert <steffen.klassert@secunet.com> Cc: Herbert Xu <herbert@gondor.apana.org.au> Cc: "David S. Miller" <davem@davemloft.net> Cc: David Howells <dhowells@redhat.com> Cc: Sabrina Dubroca <sd@queasysnail.net> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Jason Wang <jasowang@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/skbuff.h8
1 files changed, 4 insertions, 4 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 45a59c1e0cc7..d460a4cbda1c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -953,10 +953,10 @@ struct sk_buff *skb_realloc_headroom(struct sk_buff *skb,
unsigned int headroom);
struct sk_buff *skb_copy_expand(const struct sk_buff *skb, int newheadroom,
int newtailroom, gfp_t priority);
-int skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
- int offset, int len);
-int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset,
- int len);
+int __must_check skb_to_sgvec_nomark(struct sk_buff *skb, struct scatterlist *sg,
+ int offset, int len);
+int __must_check skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg,
+ int offset, int len);
int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer);
int skb_pad(struct sk_buff *skb, int pad);
#define dev_kfree_skb(a) consume_skb(a)