In the Linux kernel, the following vulnerability has been resolved:
ALSA: seq: Clear variable event pointer on read
snd_seq_read() copies a queued variable-length event header to userspace before expanding the payload. Queued variable-length events use SNDRV_SEQ_EXT_CHAINED internally, and data.ext.ptr points at the first extension cell.
The read side strips SNDRV_SEQ_EXT_* bits from data.ext.len before the copy, but it leaves data.ext.ptr untouched. A userspace sequencer client can therefore write a direct variable event to itself and read back the extension-cell kernel address from the returned header.
Clear the temporary header pointer before copy_to_user(). The original queued event remains unchanged and is still passed to snd_seq_expand_var_event(), so payload expansion keeps using the internal chain.
References
- https://git.kernel.org/stable/c/14fe4f75fd5309d6b75f8e840ada88912b374207
- https://git.kernel.org/stable/c/6b52211eba213c461f68922708a99d8190c1fcd5
- https://git.kernel.org/stable/c/705dd6dcbc0ea87351c660c1a6443f85f1001c76
- https://git.kernel.org/stable/c/74ac1ce1f4afdb3b80b6742fa28fb86c8c51d31b
- https://git.kernel.org/stable/c/c2ac9287e89916da684c2a548798351e63eb59ee
- https://git.kernel.org/stable/c/e0c3edd86414534cfd179fefe45b38c29c01ae7a
- https://git.kernel.org/stable/c/f29243c211928114f8b906e0a3fee77c236f14c8