Description

In the Linux kernel, the following vulnerability has been resolved:

mptcp: sysctl: sched: avoid using current->nsproxy

Using the 'net' structure via 'current' is not recommended for different
reasons.

First, if the goal is to use it to read or write per-netns data, this is
inconsistent with how the "generic" sysctl entries are doing: directly
by only using pointers set to the table entry, e.g. table->data. Linked
to that, the per-netns data should always be obtained from the table
linked to the netns it had been created for, which may not coincide with
the reader's or writer's netns.

Another reason is that access to current->nsproxy->netns can oops if
attempted when current->nsproxy had been dropped when the current task
is exiting. This is what syzbot found, when using acct(2):

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 1 UID: 0 PID: 5924 Comm: syz-executor Not tainted 6.13.0-rc5-syzkaller-00004-gccb98ccef0e5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:proc_scheduler+0xc6/0x3c0 net/mptcp/ctrl.c:125
Code: 03 42 80 3c 38 00 0f 85 fe 02 00 00 4d 8b a4 24 08 09 00 00 48 b8 00 00 00 00 00 fc ff df 49 8d 7c 24 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 cc 02 00 00 4d 8b 7c 24 28 48 8d 84 24 c8 00 00
RSP: 0018:ffffc900034774e8 EFLAGS: 00010206

RAX: ...

Classification

CVE ID: CVE-2025-21642

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.05% (probability of being exploited)

EPSS Percentile: 17.97% (scored less or equal to compared to others)

EPSS Date: 2025-02-17 (when was this score calculated)

References

https://git.kernel.org/stable/c/c0e394fd6b887e84da17e38aaa6c1c104f9c86c2
https://git.kernel.org/stable/c/6035702381c35a8f16757332381e58b348a9eaf9
https://git.kernel.org/stable/c/d38e26e36206ae3d544d496513212ae931d1da0a

Timeline