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Following process can cause nbd_config UAF:
1) grab nbd_config temporarily;
2) nbd_genl_disconnect() flush all recv_work() and release the
initial reference:
nbd_genl_disconnect
nbd_disconnect_and_put
nbd_disconnect
flush_workqueue(nbd->recv_workq)
if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, ...))
nbd_config_put
-> due to step 1), reference is still not zero
3) nbd_genl_reconfigure() queue recv_work() again;
nbd_genl_reconfigure
config = nbd_get_config_unlocked(nbd)
if (!config)
-> succeed
if (!test_bit(NBD_RT_BOUND, ...))
-> succeed
nbd_reconnect_socket
queue_work(nbd->recv_workq, &args->work)
4) step 1) release the reference;
5) Finially, recv_work() will trigger UAF:
recv_work
nbd_config_put(nbd)
-> nbd_config is freed
atomic_dec(&config->recv_threads)
-> UAF
Fix the problem by clearing NBD_RT_BOUND in nbd_genl_disconnect(), so
that nbd_genl_reconfigure() will fail.
Fixes: b7aa3d3938 ("nbd: add a reconfigure netlink command")
Reported-by: syzbot+6b0df248918b92c33e6a@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/675bfb65.050a0220.1a2d0d.0006.GAE@google.com/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250103092859.3574648-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.