[PATCH 5.4 299/320] inet: frags: annotate races around fqdir->dead and fqdir->high_thresh

Greg Kroah-Hartman
2022-01-24T19:41:36Z

From: Eric Dumazet <edumazet@google.com>

commit 91341fa0003befd097e190ec2a4bf63ad957c49a upstream.

Both fields can be read/written without synchronization,
add proper accessors and documentation.

Fixes: d5dd88794a13 ("inet: fix various use-after-free in defrags units")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/inet_frag.h | 11 +++++++++--
include/net/ipv6_frag.h | 3 ++-
net/ipv4/inet_fragment.c | 8 +++++---
net/ipv4/ip_fragment.c | 3 ++-
4 files changed, 18 insertions(+), 7 deletions(-)

--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -116,8 +116,15 @@ int fqdir_init(struct fqdir **fqdirp, st

static inline void fqdir_pre_exit(struct fqdir *fqdir)
{
- fqdir->high_thresh = 0; /* prevent creation of new frags */
- fqdir->dead = true;
+ /* Prevent creation of new frags.
+ * Pairs with READ_ONCE() in inet_frag_find().
+ */
+ WRITE_ONCE(fqdir->high_thresh, 0);
+
+ /* Pairs with READ_ONCE() in inet_frag_kill(), ip_expire()
+ * and ip6frag_expire_frag_queue().
+ */
+ WRITE_ONCE(fqdir->dead, true);
}
void fqdir_exit(struct fqdir *fqdir);

--- a/include/net/ipv6_frag.h
+++ b/include/net/ipv6_frag.h
@@ -67,7 +67,8 @@ ip6frag_expire_frag_queue(struct net *ne
struct sk_buff *head;

rcu_read_lock();
- if (fq->q.fqdir->dead)
+ /* Paired with the WRITE_ONCE() in fqdir_pre_exit(). */
+ if (READ_ONCE(fq->q.fqdir->dead))
goto out_rcu_unlock;
spin_lock(&fq->q.lock);

--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -204,9 +204,9 @@ void inet_frag_kill(struct inet_frag_que
/* The RCU read lock provides a memory barrier
* guaranteeing that if fqdir->dead is false then
* the hash table destruction will not start until
- * after we unlock. Paired with inet_frags_exit_net().
+ * after we unlock. Paired with fqdir_pre_exit().
*/
- if (!fqdir->dead) {
+ if (!READ_ONCE(fqdir->dead)) {
rhashtable_remove_fast(&fqdir->rhashtable, &fq->node,
fqdir->f->rhash_params);
refcount_dec(&fq->refcnt);
@@ -321,9 +321,11 @@ static struct inet_frag_queue *inet_frag
/* TODO : call from rcu_read_lock() and no longer use refcount_inc_not_zero() */
struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key)
{
+ /* This pairs with WRITE_ONCE() in fqdir_pre_exit(). */
+ long high_thresh = READ_ONCE(fqdir->high_thresh);
struct inet_frag_queue *fq = NULL, *prev;

- if (!fqdir->high_thresh || frag_mem_limit(fqdir) > fqdir->high_thresh)
+ if (!high_thresh || frag_mem_limit(fqdir) > high_thresh)
return NULL;

rcu_read_lock();
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -144,7 +144,8 @@ static void ip_expire(struct timer_list

rcu_read_lock();

- if (qp->q.fqdir->dead)
+ /* Paired with WRITE_ONCE() in fqdir_pre_exit(). */
+ if (READ_ONCE(qp->q.fqdir->dead))
goto out_rcu_unlock;

spin_lock(&qp->q.lock);