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Commit 12e35946 authored by Michal Kubecek's avatar Michal Kubecek Committed by Steffen Klassert
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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: default avatarMichal Kubecek <mkubecek@suse.cz>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarSteffen Klassert <steffen.klassert@secunet.com>
parent e9e4ea74

net/xfrm/xfrm_ipcomp.c

+6 −6
Original line number Original line 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;

	const int plen = skb->len;

	int dlen = IPCOMP_SCRATCH_SIZE;

	int dlen = IPCOMP_SCRATCH_SIZE;

	u8 *start = skb->data;

	u8 *start = skb->data;

	const int cpu = get_cpu();

	struct crypto_comp *tfm;

	u8 *scratch = *per_cpu_ptr(ipcomp_scratches, cpu);

	u8 *scratch;

	struct crypto_comp *tfm = *per_cpu_ptr(ipcd->tfms, cpu);

	int err;

	int err;





	local_bh_disable();

	local_bh_disable();

	scratch = *this_cpu_ptr(ipcomp_scratches);

	tfm = *this_cpu_ptr(ipcd->tfms);

	err = crypto_comp_compress(tfm, start, plen, scratch, &dlen);

	err = crypto_comp_compress(tfm, start, plen, scratch, &dlen);

	local_bh_enable();

	if (err)

	if (err)

		goto out;

		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);

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

	put_cpu();

	local_bh_enable();





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

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

	return 0;

	return 0;





out:

out:

	put_cpu();

	local_bh_enable();

	return err;

	return err;

}

}