Bug 1226551 (CVE-2021-47593)

Summary: VUL-0: CVE-2021-47593: kernel: mptcp: clear 'kern' flag from fallback sockets
Product: [Novell Products] SUSE Security Incidents Reporter: SMASH SMASH <smash_bz>
Component: IncidentsAssignee: Davide Benini <davide.benini>
Status: NEW --- QA Contact: Security Team bot <security-team>
Severity: Normal    
Priority: P3 - Medium CC: andrea.mattiazzo, gabriel.bertazi
Version: unspecified   
Target Milestone: ---   
Hardware: Other   
OS: Other   
URL: https://smash.suse.de/issue/411345/
Whiteboard: CVSSv3.1:SUSE:CVE-2021-47593:5.5:(AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Found By: Security Response Team Services Priority:
Business Priority: Blocker: ---
Marketing QA Status: --- IT Deployment: ---

Description SMASH SMASH 2024-06-20 09:03:25 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mptcp: clear 'kern' flag from fallback sockets

The mptcp ULP extension relies on sk->sk_sock_kern being set correctly:
It prevents setsockopt(fd, IPPROTO_TCP, TCP_ULP, "mptcp", 6); from
working for plain tcp sockets (any userspace-exposed socket).

But in case of fallback, accept() can return a plain tcp sk.
In such case, sk is still tagged as 'kernel' and setsockopt will work.

This will crash the kernel, The subflow extension has a NULL ctx->conn
mptcp socket:

BUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0
Call Trace:
 tcp_data_ready+0xf8/0x370
 [..]

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-47593
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2021/CVE-2021-47593.mbox
https://git.kernel.org/stable/c/451f1eded7f56e93aaf52eb547ba97742d9c0e97
https://git.kernel.org/stable/c/c26ac0ea3a91c210cf90452e625dc441adf3e549
https://git.kernel.org/stable/c/d6692b3b97bdc165d150f4c1505751a323a80717
https://www.cve.org/CVERecord?id=CVE-2021-47593