netdev - [PATCH net v2] packet: Move reference count in packet_sock to atomic_long

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Message-Id: <20231201131021.19999-1-daniel@iogearbox.net>
Date: Fri,  1 Dec 2023 14:10:21 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: netdev@...r.kernel.org
Cc: Daniel Borkmann <daniel@...earbox.net>,
	"The UK's National Cyber Security Centre (NCSC)" <security@...c.gov.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...nel.org
Subject: [PATCH net v2] packet: Move reference count in packet_sock to atomic_long_t

In some potential instances the reference count on struct packet_sock
could be saturated and cause overflows which gets the kernel a bit
confused. To prevent this, move to a 64-bit atomic reference count on
64-bit architectures to prevent the possibility of this type to overflow.

Because we can not handle saturation, using refcount_t is not possible
in this place. Maybe someday in the future if it changes it could be
used. Also, instead of using plain atomic64_t, use atomic_long_t instead.
32-bit machines tend to be memory-limited (i.e. anything that increases
a reference uses so much memory that you can't actually get to 2**32
references). 32-bit architectures also tend to have serious problems
with 64-bit atomics. Hence, atomic_long_t is the more natural solution.

Reported-by: "The UK's National Cyber Security Centre (NCSC)" <security@...c.gov.uk>
Co-developed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: stable@...nel.org
---
 [ No Fixes tag, needed for all currently maintained stable kernels. ]

 v1 -> v2:
   - Switch from atomic64_t to atomic_long_t (Linus)

 net/packet/af_packet.c | 16 ++++++++--------
 net/packet/internal.h  |  2 +-
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a84e00b5904b..7adf48549a3b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4300,7 +4300,7 @@ static void packet_mm_open(struct vm_area_struct *vma)
 	struct sock *sk = sock->sk;
 
 	if (sk)
-		atomic_inc(&pkt_sk(sk)->mapped);
+		atomic_long_inc(&pkt_sk(sk)->mapped);
 }
 
 static void packet_mm_close(struct vm_area_struct *vma)
@@ -4310,7 +4310,7 @@ static void packet_mm_close(struct vm_area_struct *vma)
 	struct sock *sk = sock->sk;
 
 	if (sk)
-		atomic_dec(&pkt_sk(sk)->mapped);
+		atomic_long_dec(&pkt_sk(sk)->mapped);
 }
 
 static const struct vm_operations_struct packet_mmap_ops = {
@@ -4405,7 +4405,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 
 	err = -EBUSY;
 	if (!closing) {
-		if (atomic_read(&po->mapped))
+		if (atomic_long_read(&po->mapped))
 			goto out;
 		if (packet_read_pending(rb))
 			goto out;
@@ -4508,7 +4508,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 
 	err = -EBUSY;
 	mutex_lock(&po->pg_vec_lock);
-	if (closing || atomic_read(&po->mapped) == 0) {
+	if (closing || atomic_long_read(&po->mapped) == 0) {
 		err = 0;
 		spin_lock_bh(&rb_queue->lock);
 		swap(rb->pg_vec, pg_vec);
@@ -4526,9 +4526,9 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 		po->prot_hook.func = (po->rx_ring.pg_vec) ?
 						tpacket_rcv : packet_rcv;
 		skb_queue_purge(rb_queue);
-		if (atomic_read(&po->mapped))
-			pr_err("packet_mmap: vma is busy: %d\n",
-			       atomic_read(&po->mapped));
+		if (atomic_long_read(&po->mapped))
+			pr_err("packet_mmap: vma is busy: %ld\n",
+			       atomic_long_read(&po->mapped));
 	}
 	mutex_unlock(&po->pg_vec_lock);
 
@@ -4606,7 +4606,7 @@ static int packet_mmap(struct file *file, struct socket *sock,
 		}
 	}
 
-	atomic_inc(&po->mapped);
+	atomic_long_inc(&po->mapped);
 	vma->vm_ops = &packet_mmap_ops;
 	err = 0;
 
diff --git a/net/packet/internal.h b/net/packet/internal.h
index d29c94c45159..d5d70712007a 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -122,7 +122,7 @@ struct packet_sock {
 	__be16			num;
 	struct packet_rollover	*rollover;
 	struct packet_mclist	*mclist;
-	atomic_t		mapped;
+	atomic_long_t		mapped;
 	enum tpacket_versions	tp_version;
 	unsigned int		tp_hdrlen;
 	unsigned int		tp_reserve;
-- 
2.34.1