Commit 12e35946 authored Oct 17, 2013 by Michal Kubecek Committed by Steffen Klassert Oct 18, 2013

xfrm: prevent ipcomp scratch buffer race condition



In ipcomp_compress(), sortirq is enabled too early, allowing the
per-cpu scratch buffer to be rewritten by ipcomp_decompress()
(called on the same CPU in softirq context) between populating
the buffer and copying the compressed data to the skb.

v2: as pointed out by Steffen Klassert, if we also move the
local_bh_disable() before reading the per-cpu pointers, we can
get rid of get_cpu()/put_cpu().

v3: removed ipcomp_decompress part (as explained by Herbert Xu,
it cannot be called from process context), get rid of cpu
variable (thanks to Eric Dumazet)

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

parent e9e4ea74

net/xfrm/xfrm_ipcomp.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -141,14 +141,14 @@ static int ipcomp_compress(struct xfrm_state x, struct sk_buff skb)
		const int plen = skb->len;
		int dlen = IPCOMP_SCRATCH_SIZE;
		u8 *start = skb->data;
		const int cpu = get_cpu();
		u8 scratch = per_cpu_ptr(ipcomp_scratches, cpu);
		struct crypto_comp tfm = per_cpu_ptr(ipcd->tfms, cpu);
		struct crypto_comp *tfm;
		u8 *scratch;
		int err;

		local_bh_disable();
		scratch = *this_cpu_ptr(ipcomp_scratches);
		tfm = *this_cpu_ptr(ipcd->tfms);
		err = crypto_comp_compress(tfm, start, plen, scratch, &dlen);
		local_bh_enable();
		if (err)
		goto out;

		@@ -158,13 +158,13 @@ static int ipcomp_compress(struct xfrm_state x, struct sk_buff skb)
		}

		memcpy(start + sizeof(struct ip_comp_hdr), scratch, dlen);
		put_cpu();
		local_bh_enable();

		pskb_trim(skb, dlen + sizeof(struct ip_comp_hdr));
		return 0;

		out:
		put_cpu();
		local_bh_enable();
		return err;
		}

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