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Date: Wed, 12 May 2021 06:16:08 +0200
From: Salvatore Bonaccorso <>
Subject: Re: Linux kernel: net/can/isotp: race condition leads
 to local privilege escalation


On Wed, May 12, 2021 at 12:00:33AM +0200, Norbert Slusarek wrote:
> A race condition in the CAN ISOTP networking protocol was discovered which
> allows forbidden changing of socket members after binding the socket.
> In particular, the lack of locking behavior in isotp_setsockopt() makes it
> feasible to assign the flag CAN_ISOTP_SF_BROADCAST to the socket, despite having
> previously registered a can receiver. After closing the isotp socket, the can
> receiver will still be registered and use-after-free's can be triggered in
> isotp_rcv() on the freed isotp_sock structure.
> This leads to arbitrary kernel execution by overwriting the sk_error_report()
> pointer, which can be misused in order to execute a user-controlled ROP chain to
> gain root privileges.
> The vulnerability was introduced with the introduction of SF_BROADCAST support
> in commit 921ca574cd38 ("can: isotp: add SF_BROADCAST support for functional
> addressing") in 5.11-rc1.
> In fact, commit 323a391a220c ("can: isotp: isotp_setsockopt():
> block setsockopt on bound sockets") did not effectively prevent isotp_setsockopt()
> from modifying socket members before isotp_bind().
> The requested CVE ID will be revealed along with further exploitation details
> as a response to this notice on 13th May of 2021.
> Credits: Norbert Slusarek
> *** exploit log ***
> Adjusted to work with openSUSE Tumbleweed.
> noprivs@...e:~/expl> uname -a
> Linux suse 5.12.0-1-default #1 SMP Mon Apr 26 04:25:46 UTC 2021 (5d43652) x86_64 x86_64 x86_64 GNU/Linux
> noprivs@...e:~/expl> ./lpe
> [+] entering setsockopt
> [+] entering bind
> [+] left bind with ret = 0
> [+] left setsockopt with flags = 838
> [+] race condition hit, closing and spraying socket
> [+] sending msg to run softirq with isotp_rcv()
> [+] check sudo su for root rights
> noprivs@...e:~/expl> sudo su
> suse:/home/noprivs/expl # id
> uid=0(root) gid=0(root) groups=0(root)
> suse:/home/noprivs/expl # cat /root/check
> high school student living in germany looking for an internship in info sec.
> if interested please reach out to

FTR, this issue has CVE-2021-32606[1] assigned.



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