This is a note to let you know that I've just added the patch titled
netfilter: x_tables: Use correct memory barriers.
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
netfilter-x_tables-use-correct-memory-barriers.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit dede2fc2b442beae5122be9265b53a25ad924d6b
Author: Mark Tomlinson <mark.tomlinson@xxxxxxxxxxxxxxxxxxx>
Date: Mon Mar 8 14:24:13 2021 +1300
netfilter: x_tables: Use correct memory barriers.
[ Upstream commit 175e476b8cdf2a4de7432583b49c871345e4f8a1 ]
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@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 5deb099d156d..8ec48466410a 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -376,7 +376,7 @@ 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 7df3aef39c5c..6bd31a7a27fc 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1389,7 +1389,7 @@ 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
