CVE-2026-74504

Summary

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

ALSA: seq: Fix division by zero in initialize_timer()

A userspace-driven ALSA timer (SND_UTIMER) lets an unprivileged user set the backing snd_timer's hardware resolution to an arbitrary 64-bit value via SNDRV_TIMER_IOCTL_CREATE. snd_utimer_create() only rejects zero.

When such a timer is bound to a sequencer queue, initialize_timer() computes the tick period as

tmr->ticks = 1000000000 / (r * freq);

where r is that user-controlled resolution and freq is the sequencer update rate in Hz, clamped to MIN_FREQUENCY..MAX_FREQUENCY (10..6250). A resolution of 2^63 makes the 64-bit product r * freq wrap to zero for any even freq, including DEFAULT_FREQUENCY (1000), so the division faults with a divide-by-zero.

The division runs under tmr->lock with interrupts disabled, so the oops leaves the spinlock held and hangs the CPU. It is reachable by an unprivileged user with access to /dev/snd/timer and /dev/snd/seq.

Oops: divide error: 0000 [#1] SMP KASAN PTI CPU: 7 UID: 1000 PID: 456 Comm: alsa_seq_utimer Not tainted 7.2.0-rc4+ RIP: 0010:initialize_timer.constprop.0+0x20a/0x2d0 snd_seq_timer_start+0x15e/0x2b0 snd_seq_control_queue+0x56f/0xba0 snd_seq_write+0x3e0/0x730

Reject an overflowing product with check_mul_overflow() and fall back to a single tick, which also avoids feeding a wrapped-but-nonzero divisor (e.g. 2^63 * 1000 mod 2^64 == 0, or other resolutions wrapping to a small value) into the period computation.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/d0e19932875746118e298b4c974f3b2d4aeb16fc
• https://git.kernel.org/stable/c/5260e195c53e898a4a76527d4bb2178f31795e78
• https://git.kernel.org/stable/c/42c6543ff27ea280334244458d4f52ec7133cc05
• https://git.kernel.org/stable/c/21e19688433452dfbbbe6b2bb670dea6eb92f0f6

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