{"id":"CVE-2026-74387","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-74387","summary":"ALSA: seq: midi: Serialize output teardown with event_input","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: midi: Serialize output teardown with event_input\n\nevent_process_midi() borrows msynth->output_rfile.output and then\npasses the substream to dump_midi() and snd_rawmidi_kernel_write()\nwithout synchronizing with the output open/close transition.\nmidisynth_use() also publishes output_rfile before\nsnd_rawmidi_output_params() has finished.\n\nThe last midisynth_unuse() can therefore release the same rawmidi file\nand free substream->runtime before snd_rawmidi_kernel_write1() takes\nits runtime buffer reference. That leaves the event_input path using a\nstale substream or runtime and can end in a NULL-deref or use-after-free.\n\nFix this with two pieces of synchronization. Keep a short IRQ-safe\nspinlock only for publishing or clearing output_rfile and for pairing\nthe output snapshot with an snd_use_lock_t reference. Once\nevent_process_midi() has taken that in-flight reference, it drops the\nspinlock before calling snd_seq_dump_var_event(), dump_midi(), or\nsnd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible\nrawmidi file under the same spinlock, waits for the in-flight writers\nto drain, and only then drains and releases the saved file.\nmidisynth_use() likewise opens into a local snd_rawmidi_file and\npublishes it only after snd_rawmidi_output_params() succeeds.\n\nThe buggy scenario involves two paths, with each column showing the\norder within that path:\n\nevent_input path:                     last unuse path:\n1. event_process_midi() snapshots    1. midisynth_unuse() starts\n   output_rfile.output.                 tearing down output_rfile.\n2. dump_midi() reaches               2. snd_rawmidi_kernel_release()\n   snd_rawmidi_kernel_write()           closes the output file.\n   before runtime is pinned.         3. close_substream() frees\n3. The callback keeps using             substream->runtime.\n   the borrowed substream.\n\nValidation reproduced this kernel report:\nKASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360\nRIP: 0033:0x7fde7dd0837f\nRIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360","published":"2026-08-15T05:59:02.457Z","modified":"2026-08-18T03:56:47.494903003Z","cvss":{"score":7.8,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.1.178"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/11165fe2c5ea0516debe486d91df67abbe36905e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/718f6a56b40875f19e6915799044a02df9abfd52"},{"type":"WEB","url":"https://git.kernel.org/stable/c/936641af564c3d92721704b781e36aaf223efdd2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d6fd2afb137f52bf00c5210cc44d08ed54dcffb4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ef7607ab1c8adc6258fb1b27d08e26aecdc18a58"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f5d470b808bc01f70978e22e595c6f7768313406"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74387.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74387"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-18T03:56:47.494903003Z"}}