4.4-stable review patch. If anyone has any objections, please let me know.
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From: "Jason A. Donenfeld" Jason@zx2c4.com
[ Upstream commit 48a1df65334b74bd7531f932cca5928932abf769 ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/skbuff.h | 8 +++--- net/core/skbuff.c | 65 +++++++++++++++++++++++++++++++------------------ 2 files changed, 46 insertions(+), 27 deletions(-)
--- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -879,10 +879,10 @@ struct sk_buff *skb_realloc_headroom(str 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) --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3329,24 +3329,18 @@ void __init skb_init(void) NULL); }
-/** - * skb_to_sgvec - Fill a scatter-gather list from a socket buffer - * @skb: Socket buffer containing the buffers to be mapped - * @sg: The scatter-gather list to map into - * @offset: The offset into the buffer's contents to start mapping - * @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. - */ 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 >= 24)) + return -EMSGSIZE; + if (copy > 0) { if (copy > len) copy = len; @@ -3365,6 +3359,8 @@ __skb_to_sgvec(struct sk_buff *skb, stru 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; @@ -3379,16 +3375,22 @@ __skb_to_sgvec(struct sk_buff *skb, stru }
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; @@ -3399,6 +3401,31 @@ __skb_to_sgvec(struct sk_buff *skb, stru return elt; }
+/** + * skb_to_sgvec - Fill a scatter-gather list from a socket buffer + * @skb: Socket buffer containing the buffers to be mapped + * @sg: The scatter-gather list to map into + * @offset: The offset into the buffer's contents to start mapping + * @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. Returns either + * the number of scatterlist items used, or -EMSGSIZE if the contents + * could not fit. + */ +int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len) +{ + int nsg = __skb_to_sgvec(skb, sg, offset, len, 0); + + if (nsg <= 0) + return nsg; + + sg_mark_end(&sg[nsg - 1]); + + return nsg; +} +EXPORT_SYMBOL_GPL(skb_to_sgvec); + /* As compared with skb_to_sgvec, skb_to_sgvec_nomark only map skb to given * sglist without mark the sg which contain last skb data as the end. * So the caller can mannipulate sg list as will when padding new data after @@ -3421,19 +3448,11 @@ __skb_to_sgvec(struct sk_buff *skb, stru 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);
- sg_mark_end(&sg[nsg - 1]); - - return nsg; -} -EXPORT_SYMBOL_GPL(skb_to_sgvec);
/** * skb_cow_data - Check that a socket buffer's data buffers are writable