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netfilter: nf_ct_ftp: prefer skb_linearize

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This uses a pseudo-linearization scheme with a 64k global buffer,
but BIG TCP arrival means IPv6 TCP stack can generate skbs
that exceed this size.

Use skb_linearize.  It should be possible to rewrite this to properly
deal with segmented skbs (i.e., only do small chunk-wise accesses),
but this is going to be a lot more intrusive than this because every
helper function needs to get the sk_buff instead of a pointer to a raw
data buffer.

In practice, provided we're really looking at FTP control channel packets,
there should never be a case where we deal with huge packets.

Fixes: 7c4e983c4f ("net: allow gso_max_size to exceed 65536")
Fixes: 0fe79f28bf ("net: allow gro_max_size to exceed 65536")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2022-08-09 15:16:34 +02:00 committed by Pablo Neira Ayuso
parent f3e124c36f
commit c783a29c7e
1 changed files with 6 additions and 18 deletions
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24
net/netfilter/nf_conntrack_ftp.c
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@ -34,11 +34,6 @@ MODULE_DESCRIPTION("ftp connection tracking helper");
MODULE_ALIAS("ip_conntrack_ftp");
MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
/* This is slow, but it's simple. --RR */
static char *ftp_buffer;
static DEFINE_SPINLOCK(nf_ftp_lock);
#define MAX_PORTS 8
static u_int16_t ports[MAX_PORTS];
static unsigned int ports_c;
@ -398,6 +393,9 @@ static int help(struct sk_buff *skb,
return NF_ACCEPT;
}
if (unlikely(skb_linearize(skb)))
return NF_DROP;
th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
if (th == NULL)
return NF_ACCEPT;
@ -411,12 +409,8 @@ static int help(struct sk_buff *skb,
}
datalen = skb->len - dataoff;
spin_lock_bh(&nf_ftp_lock);
fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
if (!fb_ptr) {
spin_unlock_bh(&nf_ftp_lock);
return NF_ACCEPT;
}
spin_lock_bh(&ct->lock);
fb_ptr = skb->data + dataoff;
ends_in_nl = (fb_ptr[datalen - 1] == '\n');
seq = ntohl(th->seq) + datalen;
@ -544,7 +538,7 @@ out_update_nl:
if (ends_in_nl)
update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
out:
spin_unlock_bh(&nf_ftp_lock);
spin_unlock_bh(&ct->lock);
return ret;
}
@ -571,7 +565,6 @@ static const struct nf_conntrack_expect_policy ftp_exp_policy = {
static void __exit nf_conntrack_ftp_fini(void)
{
nf_conntrack_helpers_unregister(ftp, ports_c * 2);
kfree(ftp_buffer);
}
static int __init nf_conntrack_ftp_init(void)
@ -580,10 +573,6 @@ static int __init nf_conntrack_ftp_init(void)
NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));
ftp_buffer = kmalloc(65536, GFP_KERNEL);
if (!ftp_buffer)
return -ENOMEM;
if (ports_c == 0)
ports[ports_c++] = FTP_PORT;
@ -603,7 +592,6 @@ static int __init nf_conntrack_ftp_init(void)
ret = nf_conntrack_helpers_register(ftp, ports_c * 2);
if (ret < 0) {
pr_err("failed to register helpers\n");
kfree(ftp_buffer);
return ret;
}