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authorTakashi Iwai2020-05-07 13:44:56 +0200
committerTakashi Iwai2020-05-07 22:29:14 +0200
commitc1f6e3c818dd734c30f6a7eeebf232ba2cf3181d (patch)
treef8f8f8ef8c01671898324e506a5fdce5ed6d2da1 /sound/core
parentda7a8f1a8fc3e14c6dcc52b4098bddb8f20390be (diff)
ALSA: rawmidi: Fix racy buffer resize under concurrent accesses
The rawmidi core allows user to resize the runtime buffer via ioctl, and this may lead to UAF when performed during concurrent reads or writes: the read/write functions unlock the runtime lock temporarily during copying form/to user-space, and that's the race window. This patch fixes the hole by introducing a reference counter for the runtime buffer read/write access and returns -EBUSY error when the resize is performed concurrently against read/write. Note that the ref count field is a simple integer instead of refcount_t here, since the all contexts accessing the buffer is basically protected with a spinlock, hence we need no expensive atomic ops. Also, note that this busy check is needed only against read / write functions, and not in receive/transmit callbacks; the race can happen only at the spinlock hole mentioned in the above, while the whole function is protected for receive / transmit callbacks. Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/CAFcO6XMWpUVK_yzzCpp8_XP7+=oUpQvuBeCbMffEDkpe8jWrfg@mail.gmail.com Link: https://lore.kernel.org/r/s5heerw3r5z.wl-tiwai@suse.de Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/core')
-rw-r--r--sound/core/rawmidi.c31
1 files changed, 27 insertions, 4 deletions
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index 20dd08e1f675..2a688b711a9a 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -120,6 +120,17 @@ static void snd_rawmidi_input_event_work(struct work_struct *work)
runtime->event(runtime->substream);
}
+/* buffer refcount management: call with runtime->lock held */
+static inline void snd_rawmidi_buffer_ref(struct snd_rawmidi_runtime *runtime)
+{
+ runtime->buffer_ref++;
+}
+
+static inline void snd_rawmidi_buffer_unref(struct snd_rawmidi_runtime *runtime)
+{
+ runtime->buffer_ref--;
+}
+
static int snd_rawmidi_runtime_create(struct snd_rawmidi_substream *substream)
{
struct snd_rawmidi_runtime *runtime;
@@ -669,6 +680,11 @@ static int resize_runtime_buffer(struct snd_rawmidi_runtime *runtime,
if (!newbuf)
return -ENOMEM;
spin_lock_irq(&runtime->lock);
+ if (runtime->buffer_ref) {
+ spin_unlock_irq(&runtime->lock);
+ kvfree(newbuf);
+ return -EBUSY;
+ }
oldbuf = runtime->buffer;
runtime->buffer = newbuf;
runtime->buffer_size = params->buffer_size;
@@ -1019,8 +1035,10 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream,
long result = 0, count1;
struct snd_rawmidi_runtime *runtime = substream->runtime;
unsigned long appl_ptr;
+ int err = 0;
spin_lock_irqsave(&runtime->lock, flags);
+ snd_rawmidi_buffer_ref(runtime);
while (count > 0 && runtime->avail) {
count1 = runtime->buffer_size - runtime->appl_ptr;
if (count1 > count)
@@ -1039,16 +1057,19 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream,
if (userbuf) {
spin_unlock_irqrestore(&runtime->lock, flags);
if (copy_to_user(userbuf + result,
- runtime->buffer + appl_ptr, count1)) {
- return result > 0 ? result : -EFAULT;
- }
+ runtime->buffer + appl_ptr, count1))
+ err = -EFAULT;
spin_lock_irqsave(&runtime->lock, flags);
+ if (err)
+ goto out;
}
result += count1;
count -= count1;
}
+ out:
+ snd_rawmidi_buffer_unref(runtime);
spin_unlock_irqrestore(&runtime->lock, flags);
- return result;
+ return result > 0 ? result : err;
}
long snd_rawmidi_kernel_read(struct snd_rawmidi_substream *substream,
@@ -1342,6 +1363,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream,
return -EAGAIN;
}
}
+ snd_rawmidi_buffer_ref(runtime);
while (count > 0 && runtime->avail > 0) {
count1 = runtime->buffer_size - runtime->appl_ptr;
if (count1 > count)
@@ -1373,6 +1395,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream,
}
__end:
count1 = runtime->avail < runtime->buffer_size;
+ snd_rawmidi_buffer_unref(runtime);
spin_unlock_irqrestore(&runtime->lock, flags);
if (count1)
snd_rawmidi_output_trigger(substream, 1);