[PATCH] ALSA: info: Check for integer overflow in snd_info_entry_write()

[PATCH] ALSA: info: Check for integer overflow in snd_info_entry_write()

[Erick Reyes]

Commit 4adb7bcbcb69 ("ALSA: core: Use seq_file for text proc file
reads") heavily refactored ALSA procfs and fixed the overflow as
a side-effect, so this fix only applies to kernels < 4.2 and
there is no upstream equivalent

snd_info_entry_write() resizes the buffer with an unsigned long
size argument that gets truncated because resize_info_buffer()
takes the size parameter as an unsigned int. On 64-bit kernels,
this causes the following copy_to_user() to write out-of-bounds
if (pos + count) can't be represented by an unsigned int.

Signed-off-by: Siqi Lin <siqilin@google.com>
Signed-off-by: Erick Reyes <erickreyes@google.com>
---
 sound/core/info.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sound/core/info.c b/sound/core/info.c
index 9f404e965ea2..08832c973a53 100644
--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -253,6 +253,7 @@ static ssize_t snd_info_entry_write(struct file *file, const char __user *buffer
 	struct snd_info_buffer *buf;
 	ssize_t size = 0;
 	loff_t pos;
+	unsigned long realloc_size;
 
 	data = file->private_data;
 	if (snd_BUG_ON(!data))
@@ -261,7 +262,8 @@ static ssize_t snd_info_entry_write(struct file *file, const char __user *buffer
 	pos = *offset;
 	if (pos < 0 || (long) pos != pos || (ssize_t) count < 0)
 		return -EIO;
-	if ((unsigned long) pos + (unsigned long) count < (unsigned long) pos)
+	realloc_size = (unsigned long) pos + (unsigned long) count;
+	if (realloc_size < (unsigned long) pos || realloc_size > UINT_MAX)
 		return -EIO;
 	switch (entry->content) {
 	case SNDRV_INFO_CONTENT_TEXT:
-- 
2.18.0.865.gffc8e1a3cd6-goog

Re: [PATCH] ALSA: info: Check for integer overflow in snd_info_entry_write()

[Greg KH]

On Wed, Aug 15, 2018 at 05:55:48PM -0700, Erick Reyes wrote:
> Commit 4adb7bcbcb69 ("ALSA: core: Use seq_file for text proc file
> reads") heavily refactored ALSA procfs and fixed the overflow as
> a side-effect, so this fix only applies to kernels < 4.2 and
> there is no upstream equivalent

Thanks for the patch.  I'll queue this up for 3.18.

greg k-h

Patch "ALSA: info: Check for integer overflow in snd_info_entry_write()" has been added to the 3.18-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    ALSA: info: Check for integer overflow in snd_info_entry_write()

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     alsa-info-check-for-integer-overflow-in-snd_info_entry_write.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From erickreyes@google.com  Thu Aug 16 12:07:22 2018
From: Erick Reyes <erickreyes@google.com>
Date: Wed, 15 Aug 2018 17:55:48 -0700
Subject: ALSA: info: Check for integer overflow in snd_info_entry_write()
To: stable@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>, kernel-team@android.com, Vinod Koul <vkoul@kernel.org>, Joe Perches <joe@perches.com>, Al Viro <viro@zeniv.linux.org.uk>, alsa-devel@alsa-project.org, Erick Reyes <erickreyes@google.com>, Siqi Lin <siqilin@google.com>
Message-ID: <20180816005548.151269-1-erickreyes@google.com>

From: Erick Reyes <erickreyes@google.com>

Commit 4adb7bcbcb69 ("ALSA: core: Use seq_file for text proc file
reads") heavily refactored ALSA procfs and fixed the overflow as
a side-effect, so this fix only applies to kernels < 4.2 and
there is no upstream equivalent

snd_info_entry_write() resizes the buffer with an unsigned long
size argument that gets truncated because resize_info_buffer()
takes the size parameter as an unsigned int. On 64-bit kernels,
this causes the following copy_to_user() to write out-of-bounds
if (pos + count) can't be represented by an unsigned int.

Signed-off-by: Siqi Lin <siqilin@google.com>
Signed-off-by: Erick Reyes <erickreyes@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 sound/core/info.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -253,6 +253,7 @@ static ssize_t snd_info_entry_write(stru
 	struct snd_info_buffer *buf;
 	ssize_t size = 0;
 	loff_t pos;
+	unsigned long realloc_size;
 
 	data = file->private_data;
 	if (snd_BUG_ON(!data))
@@ -261,7 +262,8 @@ static ssize_t snd_info_entry_write(stru
 	pos = *offset;
 	if (pos < 0 || (long) pos != pos || (ssize_t) count < 0)
 		return -EIO;
-	if ((unsigned long) pos + (unsigned long) count < (unsigned long) pos)
+	realloc_size = (unsigned long) pos + (unsigned long) count;
+	if (realloc_size < (unsigned long) pos || realloc_size > UINT_MAX)
 		return -EIO;
 	switch (entry->content) {
 	case SNDRV_INFO_CONTENT_TEXT:


Patches currently in stable-queue which might be from erickreyes@google.com are

queue-3.18/alsa-info-check-for-integer-overflow-in-snd_info_entry_write.patch