[PATCH 6.12.y 5/5] inet: frags: publish queues before arming timer

[Sasha Levin <sashal@kernel.org>]

From: Zhiling Zou <zhilinz@nebusec.ai>

[ Upstream commit 653d7ddf6cba867777a3d14c4f83ace008c5ad13 ]

inet_frag_create() arms the fragment queue timer before inserting the
queue into the fqdir rhashtable. If the namespace fragment timeout is
zero or negative, the timer can run before the queue is published.

The timer callback then marks the queue complete, tries to remove a node
that is not in the hash table yet, and drops the anticipated hash
reference. Creation can subsequently publish the completed queue without
restoring that reference, leaving a stale hash node after the caller drops
the remaining reference.

Publish the queue first and arm the timer while holding the queue lock.
This makes timer expiry wait until the queue is visible in the hash table,
so inet_frag_kill() can remove the node and balance the hash reference.

Fixes: 648700f76b03 ("inet: frags: use rhashtables for reassembly units")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zhiling Zou <zhilinz@nebusec.ai>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Link: https://patch.msgid.link/bf66785e7c0c139d7a1900e2f01faeeab344b960.1784948849.git.zhilinz@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/inet_fragment.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 91e598e0a6dca..ea3f15f59c723 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -393,8 +393,8 @@ static struct inet_frag_queue *inet_frag_create(struct fqdir *fqdir,
 		*prev = ERR_PTR(-ENOMEM);
 		return NULL;
 	}
-	mod_timer(&q->timer, jiffies + fqdir->timeout);
 
+	spin_lock_bh(&q->lock);
 	*prev = rhashtable_lookup_get_insert_key(&fqdir->rhashtable, &q->key,
 						 &q->node, f->rhash_params);
 	if (*prev) {
@@ -402,13 +402,13 @@ static struct inet_frag_queue *inet_frag_create(struct fqdir *fqdir,
 		 * we need to cancel what inet_frag_alloc()
 		 * anticipated.
 		 */
-		int refs = 1;
-
 		q->flags |= INET_FRAG_COMPLETE;
-		inet_frag_kill(q, &refs);
-		inet_frag_putn(q, refs);
+		spin_unlock_bh(&q->lock);
+		inet_frag_putn(q, 2);
 		return NULL;
 	}
+	mod_timer(&q->timer, jiffies + fqdir->timeout);
+	spin_unlock_bh(&q->lock);
 	return q;
 }
 
-- 
2.53.0