netfilter: x_tables: avoid leaking percpu counter pointers

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[ Upstream commit f7f2fbb0e8 ]

The native and compat get-entries paths copy the fixed rule entry header
from the kernelized rule blob to userspace before overwriting the entry's
counter fields with a sanitized counter snapshot.

On SMP kernels, entry->counters.pcnt contains the percpu allocation
address used by x_tables rule counters. A caller can provide a userspace
buffer that faults during the initial fixed-header copy after pcnt has
been copied but before the later sanitized counter copy runs. The syscall
then returns -EFAULT while leaving the raw percpu pointer in userspace.

Copy only the fixed entry prefix before counters from the kernelized rule
blob, then copy the sanitized counter snapshot into the counter field.
Apply this ordering to the IPv4, IPv6, and ARP native and compat
get-entries implementations so a fault cannot expose the internal percpu
counter pointer.

Fixes: 71ae0dff02 ("netfilter: xtables: use percpu rule counters")
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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This commit is contained in:

Kyle Zeng 2026-06-06 01:10:31 -07:00 • committed by Greg Kroah-Hartman

parent c85e8d5e23

commit 0b35dc8527

3 changed files with 18 additions and 27 deletions

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15

net/ipv4/netfilter/arp_tables.c

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15

net/ipv4/netfilter/ip_tables.c

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15

net/ipv6/netfilter/ip6_tables.c

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