6.12-stable review patch. If anyone has any objections, please let me know.
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From: Murad Masimov m.masimov@mt-integration.ru
[ Upstream commit bca0902e61731a75fc4860c8720168d9f1bae3b6 ]
If an AX25 device is bound to a socket by setting the SO_BINDTODEVICE socket option, a refcount leak will occur in ax25_release().
Commit 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()") added decrement of device refcounts in ax25_release(). In order for that to work correctly the refcounts must already be incremented when the device is bound to the socket. An AX25 device can be bound to a socket by either calling ax25_bind() or setting SO_BINDTODEVICE socket option. In both cases the refcounts should be incremented, but in fact it is done only in ax25_bind().
This bug leads to the following issue reported by Syzkaller:
================================================================ refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 1 PID: 5932 at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31 Modules linked in: CPU: 1 UID: 0 PID: 5932 Comm: syz-executor424 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31 Call Trace: <TASK> __refcount_dec include/linux/refcount.h:336 [inline] refcount_dec include/linux/refcount.h:351 [inline] ref_tracker_free+0x710/0x820 lib/ref_tracker.c:236 netdev_tracker_free include/linux/netdevice.h:4156 [inline] netdev_put include/linux/netdevice.h:4173 [inline] netdev_put include/linux/netdevice.h:4169 [inline] ax25_release+0x33f/0xa10 net/ax25/af_ax25.c:1069 __sock_release+0xb0/0x270 net/socket.c:640 sock_close+0x1c/0x30 net/socket.c:1408 ... do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f ... </TASK> ================================================================
Fix the implementation of ax25_setsockopt() by adding increment of refcounts for the new device bound, and decrement of refcounts for the old unbound device.
Fixes: 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()") Reported-by: syzbot+33841dc6aa3e1d86b78a@syzkaller.appspotmail.com Signed-off-by: Murad Masimov m.masimov@mt-integration.ru Link: https://patch.msgid.link/20250203091203.1744-1-m.masimov@mt-integration.ru Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ax25/af_ax25.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index aa6c714892ec9..9f3b8b682adb2 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -685,6 +685,15 @@ static int ax25_setsockopt(struct socket *sock, int level, int optname, break; }
+ if (ax25->ax25_dev) { + if (dev == ax25->ax25_dev->dev) { + rcu_read_unlock(); + break; + } + netdev_put(ax25->ax25_dev->dev, &ax25->dev_tracker); + ax25_dev_put(ax25->ax25_dev); + } + ax25->ax25_dev = ax25_dev_ax25dev(dev); if (!ax25->ax25_dev) { rcu_read_unlock(); @@ -692,6 +701,8 @@ static int ax25_setsockopt(struct socket *sock, int level, int optname, break; } ax25_fillin_cb(ax25, ax25->ax25_dev); + netdev_hold(dev, &ax25->dev_tracker, GFP_ATOMIC); + ax25_dev_hold(ax25->ax25_dev); rcu_read_unlock(); break;