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Stefano Garzarella a2a4346eea vsock: fix lock inversion in vsock_assign_transport()
commit f7c877e753 upstream.

Syzbot reported a potential lock inversion deadlock between
vsock_register_mutex and sk_lock-AF_VSOCK when vsock_linger() is called.

The issue was introduced by commit 687aa0c558 ("vsock: Fix
transport_* TOCTOU") which added vsock_register_mutex locking in
vsock_assign_transport() around the transport->release() call, that can
call vsock_linger(). vsock_assign_transport() can be called with sk_lock
held. vsock_linger() calls sk_wait_event() that temporarily releases and
re-acquires sk_lock. During this window, if another thread hold
vsock_register_mutex while trying to acquire sk_lock, a circular
dependency is created.

Fix this by releasing vsock_register_mutex before calling
transport->release() and vsock_deassign_transport(). This is safe
because we don't need to hold vsock_register_mutex while releasing the
old transport, and we ensure the new transport won't disappear by
obtaining a module reference first via try_module_get().

Reported-by: syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com
Tested-by: syzbot+10e35716f8e4929681fa@syzkaller.appspotmail.com
Fixes: 687aa0c558 ("vsock: Fix transport_* TOCTOU")
Cc: mhal@rbox.co
Cc: stable@vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/20251021121718.137668-1-sgarzare@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-10-29 14:10:23 +01:00
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Linux kernel
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There are several guides for kernel developers and users. These guides can
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