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Subject[080/105] netfilter: xtables: fix reentrancy
2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Eric Dumazet <eric.dumazet@gmail.com>

commit db856674ac69e31946e56085239757cca3f7655f upstream.

commit f3c5c1bfd4308 (make ip_tables reentrant) introduced a race in
handling the stackptr restore, at the end of ipt_do_table()

We should do it before the call to xt_info_rdunlock_bh(), or we allow
cpu preemption and another cpu overwrites stackptr of original one.

A second fix is to change the underflow test to check the origptr value
instead of 0 to detect underflow, or else we allow a jump from different
hooks.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/ipv4/netfilter/ip_tables.c | 4 ++--
net/ipv6/netfilter/ip6_tables.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -387,7 +387,7 @@ ipt_do_table(struct sk_buff *skb,
verdict = (unsigned)(-v) - 1;
break;
}
- if (*stackptr == 0) {
+ if (*stackptr <= origptr) {
e = get_entry(table_base,
private->underflow[hook]);
pr_debug("Underflow (this is normal) "
@@ -427,10 +427,10 @@ ipt_do_table(struct sk_buff *skb,
/* Verdict */
break;
} while (!acpar.hotdrop);
- xt_info_rdunlock_bh();
pr_debug("Exiting %s; resetting sp from %u to %u\n",
__func__, *stackptr, origptr);
*stackptr = origptr;
+ xt_info_rdunlock_bh();
#ifdef DEBUG_ALLOW_ALL
return NF_ACCEPT;
#else
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -410,7 +410,7 @@ ip6t_do_table(struct sk_buff *skb,
verdict = (unsigned)(-v) - 1;
break;
}
- if (*stackptr == 0)
+ if (*stackptr <= origptr)
e = get_entry(table_base,
private->underflow[hook]);
else
@@ -441,8 +441,8 @@ ip6t_do_table(struct sk_buff *skb,
break;
} while (!acpar.hotdrop);

- xt_info_rdunlock_bh();
*stackptr = origptr;
+ xt_info_rdunlock_bh();

#ifdef DEBUG_ALLOW_ALL
return NF_ACCEPT;



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