diff options
| author | Zhang Cen <rollkingzzc@gmail.com> | 2026-05-20 18:32:49 +0800 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2026-05-20 13:10:40 +0200 |
| commit | 60a1969fae6209644698fca91c185d153674f631 (patch) | |
| tree | 4c4e1d98b5979befbb153c1ba2b02d0af008eb3b /sound | |
| parent | a69b677e47a80319ce148d61cc29a2b57006e78d (diff) | |
| download | linux-next-history-60a1969fae6209644698fca91c185d153674f631.tar.gz | |
ALSA: seq: Serialize UMP output teardown with event_input
seq_ump_process_event() borrows client->out_rfile.output without
synchronizing with the first-open and last-close transition in
seq_ump_client_open() and seq_ump_client_close().
The last output unuse can therefore drop opened[STR_OUT] to zero and
release the rawmidi file while an in-flight event_input callback is still
inside snd_rawmidi_kernel_write(). That leaves the rawmidi substream
runtime exposed to teardown before the write path has taken its own
buffer reference.
Add a per-client rwlock for the event_input-visible output file. Publish
a newly opened output file under the write side, and hold the read side
from the output lookup through snd_rawmidi_kernel_write(). The last
output close copies and clears the visible output file under the write
side, then drops the lock and releases the saved rawmidi file. Use
IRQ-safe rwlock guards because event_input can also be reached from
atomic sequencer delivery.
The buggy scenario involves two paths, with each column showing the
order within that path:
path A label: event_input path path B label: last unuse path
1. seq_ump_process_event() reads 1. seq_ump_client_close()
client->out_rfile.output. drops opened[STR_OUT] to zero.
2. snd_rawmidi_kernel_write1() 2. snd_rawmidi_kernel_release()
has not yet pinned runtime. closes the output file.
3. The writer continues using 3. close_substream() frees
the borrowed substream. substream->runtime.
This keeps the output substream and runtime alive for the full
event_input write while keeping rawmidi release outside the rwlock.
KASAN reproduced this as a slab-use-after-free in
snd_rawmidi_kernel_write1(), with allocation through
seq_ump_use()/snd_seq_port_connect() and free through
seq_ump_unuse()/snd_seq_port_disconnect().
Suggested-by: Takashi Iwai <tiwai@suse.de>
Validation reproduced this kernel report:
KASAN slab-use-after-free in snd_rawmidi_kernel_write1+0x9d/0x400
RIP: 0033:0x7f5528af837f
Read of size 8
Call trace:
dump_stack_lvl+0x73/0xb0 (?:?)
print_report+0xd1/0x650 (?:?)
srso_alias_return_thunk+0x5/0xfbef5 (?:?)
__virt_addr_valid+0x1a7/0x340 (?:?)
kasan_complete_mode_report_info+0x64/0x200 (?:?)
kasan_report+0xf7/0x130 (?:?)
snd_rawmidi_kernel_write1+0x9d/0x400 (?:?)
__asan_load8+0x82/0xb0 (?:?)
update_stack_state+0x1ef/0x2d0 (?:?)
snd_rawmidi_kernel_write+0x1a/0x20 (?:?)
seq_ump_process_event+0xd4/0x120 (sound/core/seq/seq_ump_client.c:82)
__snd_seq_deliver_single_event+0x8a/0xe0 (?:?)
snd_seq_deliver_from_ump+0x2b2/0xd60 (?:?)
lock_acquire+0x14e/0x2e0 (?:?)
find_held_lock+0x31/0x90 (?:?)
snd_seq_port_use_ptr+0xa6/0xe0 (?:?)
__kasan_check_write+0x18/0x20 (?:?)
do_raw_read_unlock+0x32/0xa0 (?:?)
_raw_read_unlock+0x26/0x50 (?:?)
snd_seq_deliver_single_event+0x45c/0x4b0 (?:?)
snd_seq_deliver_event+0x10d/0x1b0 (?:?)
snd_seq_client_enqueue_event+0x192/0x240 (?:?)
snd_seq_write+0x2cd/0x450 (?:?)
apparmor_file_permission+0x20/0x30 (?:?)
security_file_permission+0x51/0x60 (?:?)
vfs_write+0x1ce/0x850 (?:?)
__fget_files+0x12b/0x220 (?:?)
lock_release+0xc8/0x2a0 (?:?)
__rcu_read_unlock+0x74/0x2d0 (?:?)
__fget_files+0x135/0x220 (?:?)
ksys_write+0x15a/0x180 (?:?)
rcu_is_watching+0x24/0x60 (?:?)
__x64_sys_write+0x46/0x60 (?:?)
x64_sys_call+0x7d/0x20d0 (?:?)
do_syscall_64+0xc1/0x360 (arch/x86/entry/syscall_64.c:87)
entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)
Fixes: 81fd444aa371 ("ALSA: seq: Bind UMP device")
Signed-off-by: Zhang Cen <rollkingzzc@gmail.com>
Link: https://patch.msgid.link/20260520103249.3048345-1-rollkingzzc@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound')
| -rw-r--r-- | sound/core/seq/seq_ump_client.c | 22 |
1 files changed, 18 insertions, 4 deletions
diff --git a/sound/core/seq/seq_ump_client.c b/sound/core/seq/seq_ump_client.c index 9079ccfdc8666..ccd93599b493b 100644 --- a/sound/core/seq/seq_ump_client.c +++ b/sound/core/seq/seq_ump_client.c @@ -37,6 +37,7 @@ struct seq_ump_client { struct snd_ump_endpoint *ump; /* assigned endpoint */ int seq_client; /* sequencer client id */ int opened[2]; /* current opens for each direction */ + rwlock_t output_lock; /* protects out_rfile output access */ struct snd_rawmidi_file out_rfile; /* rawmidi for output */ struct seq_ump_input_buffer input; /* input parser context */ void *ump_info[SNDRV_UMP_MAX_BLOCKS + 1]; /* shadow of seq client ump_info */ @@ -88,6 +89,7 @@ static int seq_ump_process_event(struct snd_seq_event *ev, int direct, unsigned char type; int len; + guard(read_lock_irqsave)(&client->output_lock); substream = client->out_rfile.output; if (!substream) return -ENODEV; @@ -106,6 +108,7 @@ static int seq_ump_process_event(struct snd_seq_event *ev, int direct, static int seq_ump_client_open(struct seq_ump_client *client, int dir) { struct snd_ump_endpoint *ump = client->ump; + struct snd_rawmidi_file rfile = {}; int err; guard(mutex)(&ump->open_mutex); @@ -113,9 +116,11 @@ static int seq_ump_client_open(struct seq_ump_client *client, int dir) err = snd_rawmidi_kernel_open(&ump->core, 0, SNDRV_RAWMIDI_LFLG_OUTPUT | SNDRV_RAWMIDI_LFLG_APPEND, - &client->out_rfile); + &rfile); if (err < 0) return err; + scoped_guard(write_lock_irqsave, &client->output_lock) + client->out_rfile = rfile; } client->opened[dir]++; return 0; @@ -125,11 +130,19 @@ static int seq_ump_client_open(struct seq_ump_client *client, int dir) static int seq_ump_client_close(struct seq_ump_client *client, int dir) { struct snd_ump_endpoint *ump = client->ump; + struct snd_rawmidi_file rfile = {}; guard(mutex)(&ump->open_mutex); - if (!--client->opened[dir]) - if (dir == STR_OUT) - snd_rawmidi_kernel_release(&client->out_rfile); + if (!--client->opened[dir]) { + if (dir == STR_OUT) { + scoped_guard(write_lock_irqsave, &client->output_lock) { + rfile = client->out_rfile; + client->out_rfile = (struct snd_rawmidi_file){}; + } + if (rfile.rmidi) + snd_rawmidi_kernel_release(&rfile); + } + } return 0; } @@ -467,6 +480,7 @@ static int snd_seq_ump_probe(struct snd_seq_device *dev) INIT_WORK(&client->group_notify_work, handle_group_notify); client->ump = ump; + rwlock_init(&client->output_lock); client->seq_client = snd_seq_create_kernel_client(card, ump->core.device, |