Re: Local DoS on single_open?

[Keith Owens <kaos@ocs.com.au>]

On Thu, 11 Sep 2003 05:55:07 +0100, 
viro@parcelfarce.linux.theplanet.co.uk wrote:
>On Thu, Sep 11, 2003 at 02:42:13PM +1000, Keith Owens wrote:
>> single_open() requires the kernel to kmalloc a buffer which lives until
>> the userspace caller closes the file.  What prevents a malicious user
>> opening the same /proc entry multiple times, allocating lots of kmalloc
>> space and causing a local DoS?
>
>Size of that buffer is limited.  IOW, it's not different from opening
>e.g. a shitload of pipes or sockets.

In some cases, the buffer size is set to hold _all_ of the output for
that particular /proc file and will be much larger than the data
reserved for files and sockets.  It is a difference in scale.

fs/proc/proc_misc.c		stat_open
fs/proc/proc_misc.c		interrupts_open
kernel/dma.c			proc_dma_open

All those functions will kmalloc a reasonably sized buffer then let the
user control the lifetime of that buffer.  Looks like a recipe for a
local DoS to me.