CVE-2024-26737
Assigner: Linux
Published: 2024-04-03T17:00:23.414Z
State: PUBLISHED
descriptions: value: 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.
affected: product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions: version: b00628b1c7d5
lessThan: 5268bb02107b
status: affected
versionType: git
version: b00628b1c7d5
lessThan: addf5e297e6c
status: affected
versionType: git
version: b00628b1c7d5
lessThan: 8327ed12e8eb
status: affected
versionType: git
version: b00628b1c7d5
lessThan: 7d80a9e745fa
status: affected
versionType: git
version: b00628b1c7d5
lessThan: 0281b919e175
status: affected
versionType: git
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions: version: 5.15
status: affected
version: 0
lessThan: 5.15
status: unaffected
versionType: custom
version: 5.15.150
lessThanOrEqual: 5.15.*
status: unaffected
versionType: custom
version: 6.1.80
lessThanOrEqual: 6.1.*
status: unaffected
versionType: custom
version: 6.6.19
lessThanOrEqual: 6.6.*
status: unaffected
versionType: custom
version: 6.7.7
lessThanOrEqual: 6.7.*
status: unaffected
versionType: custom
version: 6.8
lessThanOrEqual: *
status: unaffected
versionType: original_commit_for_fix
title: bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel
x_generator: engine: bippy-d3b290d2becc