diff mbox series

[Bionic] netfilter: x_tables: Use correct memory barriers.

Message ID 20210408184053.23263-2-tim.gardner@canonical.com
State New
Headers show
Series [Bionic] netfilter: x_tables: Use correct memory barriers. | expand

Commit Message

Tim Gardner April 8, 2021, 6:40 p.m. UTC 
From: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>

CVE-2021-29650

When a new table value was assigned, it was followed by a write memory
barrier. This ensured that all writes before this point would complete
before any writes after this point. However, to determine whether the
rules are unused, the sequence counter is read. To ensure that all
writes have been done before these reads, a full memory barrier is
needed, not just a write memory barrier. The same argument applies when
incrementing the counter, before the rules are read.

Changing to using smp_mb() instead of smp_wmb() fixes the kernel panic
reported in cc00bcaa5899 (which is still present), while still
maintaining the same speed of replacing tables.

The smb_mb() barriers potentially slow the packet path, however testing
has shown no measurable change in performance on a 4-core MIPS64
platform.

Fixes: 7f5c6d4f665b ("netfilter: get rid of atomic ops in fast path")
Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
(cherry picked from commit 175e476b8cdf2a4de7432583b49c871345e4f8a1)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
---
 include/linux/netfilter/x_tables.h | 2 +-
 net/netfilter/x_tables.c           | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 54f346a45cd0a..ae69b98b451b5 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -373,7 +373,7 @@  static inline unsigned int xt_write_recseq_begin(void)
 	 * since addend is most likely 1
 	 */
 	__this_cpu_add(xt_recseq.sequence, addend);
-	smp_wmb();
+	smp_mb();
 
 	return addend;
 }
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 399cde7de86a3..4638d42a22e40 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1250,7 +1250,7 @@  xt_replace_table(struct xt_table *table,
 	table->private = newinfo;
 
 	/* make sure all cpus see new ->private value */
-	smp_wmb();
+	smp_mb();
 
 	/*
 	 * Even though table entries have now been swapped, other CPU's