Description

In the Linux kernel, the following vulnerability has been resolved: nbd: defer config unlock in nbd_genl_connect There is one use-after-free warning when running NBD_CMD_CONNECT and NBD_CLEAR_SOCK: nbd_genl_connect nbd_alloc_and_init_config // config_refs=1 nbd_start_device // config_refs=2 set NBD_RT_HAS_CONFIG_REF open nbd // config_refs=3 recv_work done // config_refs=2 NBD_CLEAR_SOCK // config_refs=1 close nbd // config_refs=0 refcount_inc -> uaf ------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. WARNING: CPU: 24 PID: 1014 at lib/refcount.c:25 refcount_warn_saturate+0x12e/0x290 nbd_genl_connect+0x16d0/0x1ab0 genl_family_rcv_msg_doit+0x1f3/0x310 genl_rcv_msg+0x44a/0x790 The issue can be easily reproduced by adding a small delay before refcount_inc(&nbd->config_refs) in nbd_genl_connect(): mutex_unlock(&nbd->config_lock); if (!ret) { set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags); + printk("before sleep\n"); + mdelay(5 * 1000); + printk("after sleep\n"); refcount_inc(&nbd->config_refs); nbd_connect_reply(info, nbd->index); }

References 8

• git.kernel.org https://git.kernel.org/stable/c/1649714b930f9ea6233ce0810ba885999da3b5d4
• git.kernel.org https://git.kernel.org/stable/c/2e5e0665a594f076ef2b9439447bae8be293d09d
• git.kernel.org https://git.kernel.org/stable/c/330d688a5ca53857828081a3cf31b92ad1b0b3ed
• git.kernel.org https://git.kernel.org/stable/c/9a38306643874566d20f7aba7dff9e6f657b51a9
• git.kernel.org https://git.kernel.org/stable/c/ae3e7bc1f4b393ae20e5c85583eb2c6977374716
• git.kernel.org https://git.kernel.org/stable/c/c9b99c948b4fb014812afe7b5ccf2db121d22e46
• git.kernel.org https://git.kernel.org/stable/c/c9e805f6a35d1dd189a9345595a5c20e87611942
• git.kernel.org https://git.kernel.org/stable/c/cd93db1b1b4460e6ee77564024ea461e5940f69c

Remediation