netfilter: xtables: fix reentrancy
commit f3c5c1bf (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>
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