| Message ID | 20250306011745.100014-1-lizhi.xu@windriver.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | ALSA: seq: Use atomic to prevent data races in total_elements | expand |
On Thu, 06 Mar 2025 02:17:45 +0100, Lizhi Xu wrote: > > syzbot reported a data-race in snd_seq_poll / snd_seq_pool_init. [1] > > Just use atomic_set/atomic_read for handling this case. > > [1] > BUG: KCSAN: data-race in snd_seq_poll / snd_seq_pool_init > > write to 0xffff888114535610 of 4 bytes by task 7006 on cpu 1: > snd_seq_pool_init+0x1c1/0x200 sound/core/seq/seq_memory.c:469 > snd_seq_write+0x17f/0x500 sound/core/seq/seq_clientmgr.c:1022 > vfs_write+0x27d/0x920 fs/read_write.c:677 > ksys_write+0xe8/0x1b0 fs/read_write.c:731 > __do_sys_write fs/read_write.c:742 [inline] > __se_sys_write fs/read_write.c:739 [inline] > __x64_sys_write+0x42/0x50 fs/read_write.c:739 > x64_sys_call+0x287e/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:2 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > read to 0xffff888114535610 of 4 bytes by task 7005 on cpu 0: > snd_seq_total_cells sound/core/seq/seq_memory.h:83 [inline] > snd_seq_write_pool_allocated sound/core/seq/seq_clientmgr.c:95 [inline] > snd_seq_poll+0x103/0x170 sound/core/seq/seq_clientmgr.c:1139 > vfs_poll include/linux/poll.h:82 [inline] > __io_arm_poll_handler+0x1e5/0xd50 io_uring/poll.c:582 > io_arm_poll_handler+0x464/0x5b0 io_uring/poll.c:707 > io_queue_async+0x89/0x320 io_uring/io_uring.c:1925 > io_queue_sqe io_uring/io_uring.c:1954 [inline] > io_req_task_submit+0xb9/0xc0 io_uring/io_uring.c:1373 > io_handle_tw_list+0x1b9/0x200 io_uring/io_uring.c:1059 > tctx_task_work_run+0x6e/0x1c0 io_uring/io_uring.c:1123 > tctx_task_work+0x40/0x80 io_uring/io_uring.c:1141 > task_work_run+0x13a/0x1a0 kernel/task_work.c:227 > get_signal+0xe78/0x1000 kernel/signal.c:2809 > arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:337 > exit_to_user_mode_loop kernel/entry/common.c:111 [inline] > exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline] > __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] > syscall_exit_to_user_mode+0x62/0x120 kernel/entry/common.c:218 > do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89 > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > value changed: 0x00000000 -> 0x000001f4 This is harmless as it's only a reference in poll() and that's rather volatile. So changing the whole with atomic_t is an overkill only for that. OTOH, the check of pool size in the caller side is fragile, and it can purely rely on snd_seq_pool_poll_wait(). And, there, it should take the pool->lock for the data consistency. So, if any, an alternative fix would be something like below. thanks, Takashi -- 8< -- --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -1150,8 +1150,7 @@ static __poll_t snd_seq_poll(struct file *file, poll_table * wait) if (snd_seq_file_flags(file) & SNDRV_SEQ_LFLG_OUTPUT) { /* check if data is available in the pool */ - if (!snd_seq_write_pool_allocated(client) || - snd_seq_pool_poll_wait(client->pool, file, wait)) + if (snd_seq_pool_poll_wait(client->pool, file, wait)) mask |= EPOLLOUT | EPOLLWRNORM; } --- a/sound/core/seq/seq_memory.c +++ b/sound/core/seq/seq_memory.c @@ -427,6 +427,7 @@ int snd_seq_pool_poll_wait(struct snd_seq_pool *pool, struct file *file, poll_table *wait) { poll_wait(file, &pool->output_sleep, wait); + guard(spinlock_irq)(&pool->lock); return snd_seq_output_ok(pool); }
diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c index 20155e3e87c6..4a5c771ce8f9 100644 --- a/sound/core/seq/seq_memory.c +++ b/sound/core/seq/seq_memory.c @@ -21,7 +21,7 @@ static inline int snd_seq_pool_available(struct snd_seq_pool *pool) { - return pool->total_elements - atomic_read(&pool->counter); + return atomic_read(&pool->total_elements) - atomic_read(&pool->counter); } static inline int snd_seq_output_ok(struct snd_seq_pool *pool) @@ -353,7 +353,7 @@ int snd_seq_event_dup(struct snd_seq_pool *pool, struct snd_seq_event *event, extlen = event->data.ext.len & ~SNDRV_SEQ_EXT_MASK; ncells = DIV_ROUND_UP(extlen, sizeof(struct snd_seq_event)); } - if (ncells >= pool->total_elements) + if (ncells >= atomic_read(&pool->total_elements)) return -ENOMEM; err = snd_seq_cell_alloc(pool, &cell, nonblock, file, mutexp); @@ -466,7 +466,7 @@ int snd_seq_pool_init(struct snd_seq_pool *pool) /* init statistics */ pool->max_used = 0; - pool->total_elements = pool->size; + atomic_set(&pool->total_elements, pool->size); return 0; } @@ -499,7 +499,7 @@ int snd_seq_pool_done(struct snd_seq_pool *pool) ptr = pool->ptr; pool->ptr = NULL; pool->free = NULL; - pool->total_elements = 0; + atomic_set(&pool->total_elements, 0); } kvfree(ptr); @@ -523,7 +523,7 @@ struct snd_seq_pool *snd_seq_pool_new(int poolsize) spin_lock_init(&pool->lock); pool->ptr = NULL; pool->free = NULL; - pool->total_elements = 0; + atomic_set(&pool->total_elements, 0); atomic_set(&pool->counter, 0); pool->closing = 0; init_waitqueue_head(&pool->output_sleep); @@ -555,7 +555,7 @@ void snd_seq_info_pool(struct snd_info_buffer *buffer, { if (pool == NULL) return; - snd_iprintf(buffer, "%sPool size : %d\n", space, pool->total_elements); + snd_iprintf(buffer, "%sPool size : %d\n", space, atomic_read(&pool->total_elements)); snd_iprintf(buffer, "%sCells in use : %d\n", space, atomic_read(&pool->counter)); snd_iprintf(buffer, "%sPeak cells in use : %d\n", space, pool->max_used); snd_iprintf(buffer, "%sAlloc success : %d\n", space, pool->event_alloc_success); diff --git a/sound/core/seq/seq_memory.h b/sound/core/seq/seq_memory.h index 7f7a2c0b187d..812edbe8cee0 100644 --- a/sound/core/seq/seq_memory.h +++ b/sound/core/seq/seq_memory.h @@ -44,7 +44,7 @@ struct snd_seq_pool { struct snd_seq_event_cell *ptr; /* pointer to first event chunk */ struct snd_seq_event_cell *free; /* pointer to the head of the free list */ - int total_elements; /* pool size actually allocated */ + atomic_t total_elements; /* pool size actually allocated */ atomic_t counter; /* cells free */ int size; /* pool size to be allocated */ @@ -74,13 +74,13 @@ int snd_seq_event_dup(struct snd_seq_pool *pool, struct snd_seq_event *event, /* return number of unused (free) cells */ static inline int snd_seq_unused_cells(struct snd_seq_pool *pool) { - return pool ? pool->total_elements - atomic_read(&pool->counter) : 0; + return pool ? atomic_read(&pool->total_elements) - atomic_read(&pool->counter) : 0; } /* return total number of allocated cells */ static inline int snd_seq_total_cells(struct snd_seq_pool *pool) { - return pool ? pool->total_elements : 0; + return pool ? atomic_read(&pool->total_elements) : 0; } /* init pool - allocate events */
syzbot reported a data-race in snd_seq_poll / snd_seq_pool_init. [1] Just use atomic_set/atomic_read for handling this case. [1] BUG: KCSAN: data-race in snd_seq_poll / snd_seq_pool_init write to 0xffff888114535610 of 4 bytes by task 7006 on cpu 1: snd_seq_pool_init+0x1c1/0x200 sound/core/seq/seq_memory.c:469 snd_seq_write+0x17f/0x500 sound/core/seq/seq_clientmgr.c:1022 vfs_write+0x27d/0x920 fs/read_write.c:677 ksys_write+0xe8/0x1b0 fs/read_write.c:731 __do_sys_write fs/read_write.c:742 [inline] __se_sys_write fs/read_write.c:739 [inline] __x64_sys_write+0x42/0x50 fs/read_write.c:739 x64_sys_call+0x287e/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:2 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f read to 0xffff888114535610 of 4 bytes by task 7005 on cpu 0: snd_seq_total_cells sound/core/seq/seq_memory.h:83 [inline] snd_seq_write_pool_allocated sound/core/seq/seq_clientmgr.c:95 [inline] snd_seq_poll+0x103/0x170 sound/core/seq/seq_clientmgr.c:1139 vfs_poll include/linux/poll.h:82 [inline] __io_arm_poll_handler+0x1e5/0xd50 io_uring/poll.c:582 io_arm_poll_handler+0x464/0x5b0 io_uring/poll.c:707 io_queue_async+0x89/0x320 io_uring/io_uring.c:1925 io_queue_sqe io_uring/io_uring.c:1954 [inline] io_req_task_submit+0xb9/0xc0 io_uring/io_uring.c:1373 io_handle_tw_list+0x1b9/0x200 io_uring/io_uring.c:1059 tctx_task_work_run+0x6e/0x1c0 io_uring/io_uring.c:1123 tctx_task_work+0x40/0x80 io_uring/io_uring.c:1141 task_work_run+0x13a/0x1a0 kernel/task_work.c:227 get_signal+0xe78/0x1000 kernel/signal.c:2809 arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:337 exit_to_user_mode_loop kernel/entry/common.c:111 [inline] exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline] __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] syscall_exit_to_user_mode+0x62/0x120 kernel/entry/common.c:218 do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89 entry_SYSCALL_64_after_hwframe+0x77/0x7f value changed: 0x00000000 -> 0x000001f4 Reported-by: syzbot+2d373c9936c00d7e120c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2d373c9936c00d7e120c Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com> --- sound/core/seq/seq_memory.c | 12 ++++++------ sound/core/seq/seq_memory.h | 6 +++--- 2 files changed, 9 insertions(+), 9 deletions(-)