@@ -943,31 +943,36 @@ 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;
}
@@ -1221,6 +1226,7 @@ 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;
@@ -1241,12 +1247,19 @@ 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;
@@ -1254,9 +1267,6 @@ 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;
}
This is a note to let you know that I have just added a patch titled ALSA: rawmidi: Fix race at copying & updating the position to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue This patch is scheduled to be released in version 3.13.11-ckt36. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.13.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ---8<------------------------------------------------------------ From 373a7677852d7c9ace9520c8194ad246a2604a34 Mon Sep 17 00:00:00 2001 From: Takashi Iwai <tiwai@suse.de> Date: Wed, 3 Feb 2016 14:41:22 +0100 Subject: 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: Kamal Mostafa <kamal@canonical.com> --- sound/core/rawmidi.c | 34 ++++++++++++++++++++++------------ 1 file changed, 22 insertions(+), 12 deletions(-) -- 2.7.0