From 0b35dc8527ccc16b7dc34e8a3164313e68cd4e45 Mon Sep 17 00:00:00 2001 From: Kyle Zeng Date: Sat, 6 Jun 2026 01:10:31 -0700 Subject: [PATCH] netfilter: x_tables: avoid leaking percpu counter pointers [ Upstream commit f7f2fbb0e893a0238dc464f8d8c0f5609bec584f ] 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: 71ae0dff02d7 ("netfilter: xtables: use percpu rule counters") Signed-off-by: Kyle Zeng Signed-off-by: Pablo Neira Ayuso Signed-off-by: Sasha Levin --- net/ipv4/netfilter/arp_tables.c | 15 ++++++--------- net/ipv4/netfilter/ip_tables.c | 15 ++++++--------- net/ipv6/netfilter/ip6_tables.c | 15 ++++++--------- 3 files changed, 18 insertions(+), 27 deletions(-) diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c index 92bc90ee7674..2c39529769f1 100644 --- a/net/ipv4/netfilter/arp_tables.c +++ b/net/ipv4/netfilter/arp_tables.c @@ -701,14 +701,12 @@ static int copy_entries_to_user(unsigned int total_size, const struct xt_entry_target *t; e = loc_cpu_entry + off; - if (copy_to_user(userptr + off, e, sizeof(*e))) { - ret = -EFAULT; - goto free_counters; - } - if (copy_to_user(userptr + off + if (copy_to_user(userptr + off, e, + offsetof(struct arpt_entry, counters)) || + copy_to_user(userptr + off + offsetof(struct arpt_entry, counters), &counters[num], - sizeof(counters[num])) != 0) { + sizeof(counters[num]))) { ret = -EFAULT; goto free_counters; } @@ -1326,9 +1324,8 @@ static int compat_copy_entry_to_user(struct arpt_entry *e, void __user **dstptr, origsize = *size; ce = *dstptr; - if (copy_to_user(ce, e, sizeof(struct arpt_entry)) != 0 || - copy_to_user(&ce->counters, &counters[i], - sizeof(counters[i])) != 0) + if (copy_to_user(ce, e, offsetof(struct compat_arpt_entry, counters)) || + copy_to_user(&ce->counters, &counters[i], sizeof(counters[i]))) return -EFAULT; *dstptr += sizeof(struct compat_arpt_entry); diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c index aee7cd584c92..15a9e303a153 100644 --- a/net/ipv4/netfilter/ip_tables.c +++ b/net/ipv4/netfilter/ip_tables.c @@ -833,14 +833,12 @@ copy_entries_to_user(unsigned int total_size, const struct xt_entry_target *t; e = loc_cpu_entry + off; - if (copy_to_user(userptr + off, e, sizeof(*e))) { - ret = -EFAULT; - goto free_counters; - } - if (copy_to_user(userptr + off + if (copy_to_user(userptr + off, e, + offsetof(struct ipt_entry, counters)) || + copy_to_user(userptr + off + offsetof(struct ipt_entry, counters), &counters[num], - sizeof(counters[num])) != 0) { + sizeof(counters[num]))) { ret = -EFAULT; goto free_counters; } @@ -1229,9 +1227,8 @@ compat_copy_entry_to_user(struct ipt_entry *e, void __user **dstptr, origsize = *size; ce = *dstptr; - if (copy_to_user(ce, e, sizeof(struct ipt_entry)) != 0 || - copy_to_user(&ce->counters, &counters[i], - sizeof(counters[i])) != 0) + if (copy_to_user(ce, e, offsetof(struct compat_ipt_entry, counters)) || + copy_to_user(&ce->counters, &counters[i], sizeof(counters[i]))) return -EFAULT; *dstptr += sizeof(struct compat_ipt_entry); diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c index afd22ea9f555..f2de34f0de23 100644 --- a/net/ipv6/netfilter/ip6_tables.c +++ b/net/ipv6/netfilter/ip6_tables.c @@ -850,14 +850,12 @@ copy_entries_to_user(unsigned int total_size, const struct xt_entry_target *t; e = loc_cpu_entry + off; - if (copy_to_user(userptr + off, e, sizeof(*e))) { - ret = -EFAULT; - goto free_counters; - } - if (copy_to_user(userptr + off + if (copy_to_user(userptr + off, e, + offsetof(struct ip6t_entry, counters)) || + copy_to_user(userptr + off + offsetof(struct ip6t_entry, counters), &counters[num], - sizeof(counters[num])) != 0) { + sizeof(counters[num]))) { ret = -EFAULT; goto free_counters; } @@ -1246,9 +1244,8 @@ compat_copy_entry_to_user(struct ip6t_entry *e, void __user **dstptr, origsize = *size; ce = *dstptr; - if (copy_to_user(ce, e, sizeof(struct ip6t_entry)) != 0 || - copy_to_user(&ce->counters, &counters[i], - sizeof(counters[i])) != 0) + if (copy_to_user(ce, e, offsetof(struct compat_ip6t_entry, counters)) || + copy_to_user(&ce->counters, &counters[i], sizeof(counters[i]))) return -EFAULT; *dstptr += sizeof(struct compat_ip6t_entry);