CVE-2026-90220ALSA: seq: Don't leak the extension cell pointer in the bounce payload

Official description

In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: Don't leak the extension cell pointer in the bounce payload The bounce_error_event() embeds the failed event in the bounce payload by pointing data.ext.ptr at it. When that event is a queued variable-length event, its own data.ext.ptr holds the address of its first extension cell, put there by snd_seq_event_dup(). The payload goes out verbatim through snd_seq_expand_var_event(), so the address reaches userspace. That is the same address commit 705dd6dcbc0e ("ALSA: seq: Clear variable event pointer on read") removed from the event header. The read path still clears it there, just above the call that expands the payload. Embed a sanitised copy instead, treated exactly as snd_seq_read() treats the header. A stack copy is enough because delivery is synchronous and snd_seq_event_dup() copies before returning. An unprivileged client reaches this by setting SNDRV_SEQ_FILTER_BOUNCE, queueing a variable-length event to a port that does not exist and reading the bounce back. Eight bytes on 64-bit, from its own pool.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c92b2e6e418a3885758438dddcead6e954a9e095
• https://git.kernel.org/stable/c/42c3f856d13a91a0d4c302a0c6854813621136db
• https://git.kernel.org/stable/c/b1e8d40663997aacaa198f37ce6893e07aaba77a
• https://git.kernel.org/stable/c/6e6e471eef1d5d8cb056c7d364023fe048249204
• https://git.kernel.org/stable/c/59e1592d3c270ff4642d5d6dc55c545306eb0693