Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel The following race is possible between bpf_timer_cancel_and_free and bpf_timer_cancel. It will lead a UAF on the timer->timer. bpf_timer_cancel(); spin_lock(); t = timer->time; spin_unlock(); bpf_timer_cancel_and_free(); spin_lock(); t = timer->timer; timer->timer = NULL; spin_unlock(); hrtimer_cancel(&t->timer); kfree(t); /* UAF on t */ hrtimer_cancel(&t->timer); In bpf_timer_cancel_and_free, this patch frees the timer->timer after a rcu grace period. This requires a rcu_head addition to the "struct bpf_hrtimer". Another kfree(t) happens in bpf_timer_init, this does not need a kfree_rcu because it is still under the spin_lock and timer->timer has not been visible by others yet. In bpf_timer_cancel, rcu_read_lock() is added because this helper can be used in a non rcu critical section context (e.g. from a sleepable bpf prog). Other timer->timer usages in helpers.c have been audited, bpf_timer_cancel() is the only place where timer->timer is used outside of the spin_lock. Another solution considered is to mark a t->flag in bpf_timer_cancel and clear it after hrtimer_cancel() is done. In bpf_timer_cancel_and_free, it busy waits for the flag to be cleared before kfree(t). This patch goes with a straight forward solution and frees timer->timer after a rcu grace period.

Metrics

 

CVSS Version 4.0 CVSS Version 3.x CVSS Version 2.0

NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.

CVSS 4.0 Severity and Vector Strings:

NIST: NVD

N/A

NVD assessment not yet provided.

CVSS 3.x Severity and Vector Strings:

NIST: NVD

Base Score:  N/A

NVD assessment not yet provided.

ADP:  CISA-ADP

Base Score:  5.5 MEDIUM

Vector:  CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS 2.0 Severity and Vector Strings:

NIST: NVD

Base Score: N/A

NVD assessment not yet provided.

https://git.kernel.org/stable/c/0281b919e175bb9c3128bd3872ac2903e9436e3f

https://git.kernel.org/stable/c/5268bb02107b9eedfdcd51db75b407d10043368c

https://git.kernel.org/stable/c/7d80a9e745fa5b47da3bca001f186c02485c7c33

https://git.kernel.org/stable/c/8327ed12e8ebc5436bfaa1786c49988894f9c8a6

https://git.kernel.org/stable/c/addf5e297e6cbf5341f9c07720693ca9ba0057b5

CISA-ADP AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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

bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel

The following race is possible between bpf_timer_cancel_and_free
and bpf_timer_cancel. It will lead a UAF on the timer->timer.

bpf_timer_cancel();
	spin_lock();
	t = timer->time;
	spin_unlock();

					bpf_timer_cancel_and_free();
						spin_lock();
						t = timer->timer;
						timer->timer = NULL;
						spin_unlock();
						hrtimer_cancel(&t->timer);
				

kernel.org https://git.kernel.org/stable/c/0281b919e175bb9c3128bd3872ac2903e9436e3f [No types assigned]

kernel.org https://git.kernel.org/stable/c/5268bb02107b9eedfdcd51db75b407d10043368c [No types assigned]

kernel.org https://git.kernel.org/stable/c/7d80a9e745fa5b47da3bca001f186c02485c7c33 [No types assigned]

kernel.org https://git.kernel.org/stable/c/8327ed12e8ebc5436bfaa1786c49988894f9c8a6 [No types assigned]

kernel.org https://git.kernel.org/stable/c/addf5e297e6cbf5341f9c07720693ca9ba0057b5 [No types assigned]