6.18-stable review patch. If anyone has any objections, please let me know.
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From: Jakub Kicinski kuba@kernel.org
[ Upstream commit 8ef522c8a59a048117f7e05eb5213043c02f986f ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/inet_fragment.c | 4 +++- 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 025895eb6ec59..30f4fa50ee2d7 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 f7012479713ba..d7bccdc9dc693 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);