CVE-2024-26737: bpf: Fix racing between bpf_timer_cancel_and_free and bpf_timer_cancel
First published: Wed Apr 03 2024(Updated: )
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.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| redhat/kernel | <5.15.150 | 5.15.150 |
| redhat/kernel | <6.1.80 | 6.1.80 |
| redhat/kernel | <6.6.19 | 6.6.19 |
| redhat/kernel | <6.7.7 | 6.7.7 |
| redhat/kernel | <6.8 | 6.8 |
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.119-1 6.12.5-1 6.12.6-1 |
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Reference Links
- 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
- https://launchpad.net/bugs/cve/CVE-2024-26737
- https://access.redhat.com/security/cve/CVE-2024-26737
- https://lore.kernel.org/linux-cve-announce/2024040359-CVE-2024-26737-a9c3@gregkh/T
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=2273275
- https://access.redhat.com/errata/RHSA-2024:4928
- https://access.redhat.com/errata/RHSA-2024:5067
- https://access.redhat.com/errata/RHSA-2024:5066
- https://bugzilla.redhat.com/show_bug.cgi?id=2273274
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-26737
- https://nvd.nist.gov/vuln/detail/CVE-2024-26737
- https://security-tracker.debian.org/tracker/CVE-2024-26737
- https://ubuntu.com/security/CVE-2024-26737
- https://git.kernel.org/linus/0281b919e175bb9c3128bd3872ac2903e9436e3f
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