Vulnerability CVE-2024-35895
Published: 2024-05-19

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

bpf, sockmap: Prevent lock inversion deadlock in map delete elem

syzkaller started using corpuses where a BPF tracing program deletes
elements from a sockmap/sockhash map. Because BPF tracing programs can be
invoked from any interrupt context, locks taken during a map_delete_elem
operation must be hardirq-safe. Otherwise a deadlock due to lock inversion
is possible, as reported by lockdep:

CPU0 CPU1
---- ----
lock(&htab->buckets[i].lock);
local_irq_disable();
lock(&host->lock);
lock(&htab->buckets[i].lock);
<Interrupt>
lock(&host->lock);

Locks in sockmap are hardirq-unsafe by design. We expects elements to be
deleted from sockmap/sockhash only in task (normal) context with interrupts
enabled, or in softirq context.

Detect when map_delete_elem operation is invoked from a context which is
_not_ hardirq-unsafe, that is interrupts are disabled, and bail out with an
error.

Note that map updates are not affected by this issue. BPF verifier does not
allow updating sockmap/sockhash from a BPF tracing program today.

 References:
https://git.kernel.org/stable/c/f7990498b05ac41f7d6a190dc0418ef1d21bf058
https://git.kernel.org/stable/c/dd54b48db0c822ae7b520bc80751f0a0a173ef75
https://git.kernel.org/stable/c/d1e73fb19a4c872d7a399ad3c66e8ca30e0875ec
https://git.kernel.org/stable/c/a44770fed86515eedb5a7c00b787f847ebb134a5
https://git.kernel.org/stable/c/668b3074aa14829e2ac2759799537a93b60fef86
https://git.kernel.org/stable/c/6af057ccdd8e7619960aca1f0428339f213b31cd
https://git.kernel.org/stable/c/ff91059932401894e6c86341915615c5eb0eca48
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