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authorTakashi Iwai <tiwai@suse.de>2016-02-03 14:41:22 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-02-17 12:30:58 -0800
commit49ba9e222aa5a079cf89d2a86da9838aa0213a60 (patch)
treec247bac12e763355c14aa8e7dbe0cafb010c47cc /sound
parent8af97f7c418ddc9c3e7a649414c70e798b134e50 (diff)
ALSA: rawmidi: Fix race at copying & updating the position
commit 81f577542af15640cbcb6ef68baa4caa610cbbfc upstream. The rawmidi read and write functions manage runtime stream status such as runtime->appl_ptr and runtime->avail. These point where to copy the new data and how many bytes have been copied (or to be read). The problem is that rawmidi read/write call copy_from_user() or copy_to_user(), and the runtime spinlock is temporarily unlocked and relocked while copying user-space. Since the current code advances and updates the runtime status after the spin unlock/relock, the copy and the update may be asynchronous, and eventually runtime->avail might go to a negative value when many concurrent accesses are done. This may lead to memory corruption in the end. For fixing this race, in this patch, the status update code is performed in the same lock before the temporary unlock. Also, the spinlock is now taken more widely in snd_rawmidi_kernel_read1() for protecting more properly during the whole operation. BugLink: http://lkml.kernel.org/r/CACT4Y+b-dCmNf1GpgPKfDO0ih+uZCL2JV4__j-r1kdhPLSgQCQ@mail.gmail.com Reported-by: Dmitry Vyukov <dvyukov@google.com> Tested-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/rawmidi.c34
1 files changed, 22 insertions, 12 deletions
diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index 26ca02248885..795437b10082 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -942,31 +942,36 @@ static long snd_rawmidi_kernel_read1(struct snd_rawmidi_substream *substream,
unsigned long flags;
long result = 0, count1;
struct snd_rawmidi_runtime *runtime = substream->runtime;
+ unsigned long appl_ptr;
+ spin_lock_irqsave(&runtime->lock, flags);
while (count > 0 && runtime->avail) {
count1 = runtime->buffer_size - runtime->appl_ptr;
if (count1 > count)
count1 = count;
- spin_lock_irqsave(&runtime->lock, flags);
if (count1 > (int)runtime->avail)
count1 = runtime->avail;
+
+ /* update runtime->appl_ptr before unlocking for userbuf */
+ appl_ptr = runtime->appl_ptr;
+ runtime->appl_ptr += count1;
+ runtime->appl_ptr %= runtime->buffer_size;
+ runtime->avail -= count1;
+
if (kernelbuf)
- memcpy(kernelbuf + result, runtime->buffer + runtime->appl_ptr, count1);
+ memcpy(kernelbuf + result, runtime->buffer + appl_ptr, count1);
if (userbuf) {
spin_unlock_irqrestore(&runtime->lock, flags);
if (copy_to_user(userbuf + result,
- runtime->buffer + runtime->appl_ptr, count1)) {
+ runtime->buffer + appl_ptr, count1)) {
return result > 0 ? result : -EFAULT;
}
spin_lock_irqsave(&runtime->lock, flags);
}
- runtime->appl_ptr += count1;
- runtime->appl_ptr %= runtime->buffer_size;
- runtime->avail -= count1;
- spin_unlock_irqrestore(&runtime->lock, flags);
result += count1;
count -= count1;
}
+ spin_unlock_irqrestore(&runtime->lock, flags);
return result;
}
@@ -1223,6 +1228,7 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream,
unsigned long flags;
long count1, result;
struct snd_rawmidi_runtime *runtime = substream->runtime;
+ unsigned long appl_ptr;
if (!kernelbuf && !userbuf)
return -EINVAL;
@@ -1243,12 +1249,19 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream,
count1 = count;
if (count1 > (long)runtime->avail)
count1 = runtime->avail;
+
+ /* update runtime->appl_ptr before unlocking for userbuf */
+ appl_ptr = runtime->appl_ptr;
+ runtime->appl_ptr += count1;
+ runtime->appl_ptr %= runtime->buffer_size;
+ runtime->avail -= count1;
+
if (kernelbuf)
- memcpy(runtime->buffer + runtime->appl_ptr,
+ memcpy(runtime->buffer + appl_ptr,
kernelbuf + result, count1);
else if (userbuf) {
spin_unlock_irqrestore(&runtime->lock, flags);
- if (copy_from_user(runtime->buffer + runtime->appl_ptr,
+ if (copy_from_user(runtime->buffer + appl_ptr,
userbuf + result, count1)) {
spin_lock_irqsave(&runtime->lock, flags);
result = result > 0 ? result : -EFAULT;
@@ -1256,9 +1269,6 @@ static long snd_rawmidi_kernel_write1(struct snd_rawmidi_substream *substream,
}
spin_lock_irqsave(&runtime->lock, flags);
}
- runtime->appl_ptr += count1;
- runtime->appl_ptr %= runtime->buffer_size;
- runtime->avail -= count1;
result += count1;
count -= count1;
}