diff options
| author | Jakub Kicinski <kuba@kernel.org> | 2025-12-06 17:09:39 -0800 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2025-12-10 01:15:27 -0800 |
| commit | 8ef522c8a59a048117f7e05eb5213043c02f986f (patch) | |
| tree | 6cb9298eb952b574f3c38705f7aac8ddb423edaf /net | |
| parent | 2f6e056e95ff5020260ccfd85391a6474d87e4b5 (diff) | |
inet: frags: avoid theoretical race in ip_frag_reinit()
In ip_frag_reinit() we want to move the frag timeout timer into
the future. If the timer fires in the meantime we inadvertently
scheduled it again, and since the timer assumes a ref on frag_queue
we need to acquire one to balance things out.
This is technically racy, we should have acquired the reference
_before_ we touch the timer, it may fire again before we take the ref.
Avoid this entire dance by using mod_timer_pending() which only modifies
the timer if its pending (and which exists since Linux v2.6.30)
Note that this was the only place we ever took a ref on frag_queue
since Eric's conversion to RCU. So we could potentially replace
the whole refcnt field with an atomic flag and a bit more RCU.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251207010942.1672972-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/ipv4/inet_fragment.c | 4 | ||||
| -rw-r--r-- | net/ipv4/ip_fragment.c | 4 |
2 files changed, 4 insertions, 4 deletions
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c index 025895eb6ec5..30f4fa50ee2d 100644 --- a/net/ipv4/inet_fragment.c +++ b/net/ipv4/inet_fragment.c @@ -327,7 +327,9 @@ static struct inet_frag_queue *inet_frag_alloc(struct fqdir *fqdir, timer_setup(&q->timer, f->frag_expire, 0); spin_lock_init(&q->lock); - /* One reference for the timer, one for the hash table. */ + /* One reference for the timer, one for the hash table. + * We never take any extra references, only decrement this field. + */ refcount_set(&q->refcnt, 2); return q; diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index f7012479713b..d7bccdc9dc69 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -242,10 +242,8 @@ static int ip_frag_reinit(struct ipq *qp) { unsigned int sum_truesize = 0; - if (!mod_timer(&qp->q.timer, jiffies + qp->q.fqdir->timeout)) { - refcount_inc(&qp->q.refcnt); + if (!mod_timer_pending(&qp->q.timer, jiffies + qp->q.fqdir->timeout)) return -ETIMEDOUT; - } sum_truesize = inet_frag_rbtree_purge(&qp->q.rb_fragments, SKB_DROP_REASON_FRAG_TOO_FAR); |