ALSA: seq: Fix racy cell insertions during snd_seq_pool_done()

commit c520ff3d03f0b5db7146d9beed6373ad5d2a5e0e upstream.

When snd_seq_pool_done() is called, it marks the closing flag to
refuse the further cell insertions.  But snd_seq_pool_done() itself
doesn't clear the cells but just waits until all cells are cleared by
the caller side.  That is, it's racy, and this leads to the endless
stall as syzkaller spotted.

This patch addresses the racy by splitting the setup of pool->closing
flag out of snd_seq_pool_done(), and calling it properly before
snd_seq_pool_done().

BugLink: http://lkml.kernel.org/r/CACT4Y+aqqy8bZA1fFieifNxR2fAfFQQABcBHj801+u5ePV0URw@mail.gmail.com
Reported-and-tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c
index a4dabd55e3978a6af029f215b45810b61bd043ac..4a240416b830a8e8f40fe87a9dfdba09a8ebbf10 100644 (file)
--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1921,6 +1921,7 @@ static int snd_seq_ioctl_set_client_pool(struct snd_seq_client *client,
             info.output_pool != client->pool->size)) {
                if (snd_seq_write_pool_allocated(client)) {
                        /* remove all existing cells */
+                       snd_seq_pool_mark_closing(client->pool);
                        snd_seq_queue_client_leave_cells(client->number);
                        snd_seq_pool_done(client->pool);
                }

diff --git a/sound/core/seq/seq_fifo.c b/sound/core/seq/seq_fifo.c
index 1d5acbe0c08bdf14db4253f95391fa5e99059610..a3d204bdc7a6eb2c7df28d874971fa0bda5f98e4 100644 (file)
--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -70,6 +70,9 @@ void snd_seq_fifo_delete(struct snd_seq_fifo **fifo)
                return;
        *fifo = NULL;
 
+       if (f->pool)
+               snd_seq_pool_mark_closing(f->pool);
+
        snd_seq_fifo_clear(f);
 
        /* wake up clients if any */

diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c
index c850345c43b53dd5616b155f34f741d0ca30701c..b855c087cd8ad5e6cfd02397f854a204db10fcfb 100644 (file)
--- a/sound/core/seq/seq_memory.c
+++ b/sound/core/seq/seq_memory.c
@@ -414,6 +414,18 @@ int snd_seq_pool_init(struct snd_seq_pool *pool)
        return 0;
 }
 
+/* refuse the further insertion to the pool */
+void snd_seq_pool_mark_closing(struct snd_seq_pool *pool)
+{
+       unsigned long flags;
+
+       if (snd_BUG_ON(!pool))
+               return;
+       spin_lock_irqsave(&pool->lock, flags);
+       pool->closing = 1;
+       spin_unlock_irqrestore(&pool->lock, flags);
+}
+
 /* remove events */
 int snd_seq_pool_done(struct snd_seq_pool *pool)
 {
@@ -425,10 +437,6 @@ int snd_seq_pool_done(struct snd_seq_pool *pool)
                return -EINVAL;
 
        /* wait for closing all threads */
-       spin_lock_irqsave(&pool->lock, flags);
-       pool->closing = 1;
-       spin_unlock_irqrestore(&pool->lock, flags);
-
        if (waitqueue_active(&pool->output_sleep))
                wake_up(&pool->output_sleep);
 
@@ -491,6 +499,7 @@ int snd_seq_pool_delete(struct snd_seq_pool **ppool)
        *ppool = NULL;
        if (pool == NULL)
                return 0;
+       snd_seq_pool_mark_closing(pool);
        snd_seq_pool_done(pool);
        kfree(pool);
        return 0;

diff --git a/sound/core/seq/seq_memory.h b/sound/core/seq/seq_memory.h
index 4a2ec779b8a701b1aba2402e9de583878f7a39ca..32f959c17786d9ac8c071ba0e6fd070dc06da78b 100644 (file)
--- a/sound/core/seq/seq_memory.h
+++ b/sound/core/seq/seq_memory.h
@@ -84,6 +84,7 @@ static inline int snd_seq_total_cells(struct snd_seq_pool *pool)
 int snd_seq_pool_init(struct snd_seq_pool *pool);
 
 /* done pool - free events */
+void snd_seq_pool_mark_closing(struct snd_seq_pool *pool);
 int snd_seq_pool_done(struct snd_seq_pool *pool);
 
 /* create pool */