[81/85] drivers/cdrom/cdrom.c: use kzalloc() for failing hardware

From: Ben Hutchings
Date: Wed Jul 24 2013 - 10:14:48 EST

3.2.49-rc1 review patch. If anyone has any objections, please let me know.


From: Jonathan Salwan <jonathan.salwan@xxxxxxxxx>

commit 542db01579fbb7ea7d1f7bb9ddcef1559df660b2 upstream.

In drivers/cdrom/cdrom.c mmc_ioctl_cdrom_read_data() allocates a memory
area with kmalloc in line 2885.

2885 cgc->buffer = kmalloc(blocksize, GFP_KERNEL);
2886 if (cgc->buffer == NULL)
2887 return -ENOMEM;

In line 2908 we can find the copy_to_user function:

2908 if (!ret && copy_to_user(arg, cgc->buffer, blocksize))

The cgc->buffer is never cleaned and initialized before this function.
If ret = 0 with the previous basic block, it's possible to display some
memory bytes in kernel space from userspace.

When we read a block from the disk it normally fills the ->buffer but if
the drive is malfunctioning there is a chance that it would only be
partially filled. The result is an leak information to userspace.

Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
drivers/cdrom/cdrom.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -2885,7 +2885,7 @@ static noinline int mmc_ioctl_cdrom_read
if (lba < 0)
return -EINVAL;

- cgc->buffer = kmalloc(blocksize, GFP_KERNEL);
+ cgc->buffer = kzalloc(blocksize, GFP_KERNEL);
if (cgc->buffer == NULL)
return -ENOMEM;

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