lkml.org 
[lkml]   [2020]   [May]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] x86/ioperm: fix a memory leak bug
Date
Jay,

Jay Lang <jaytlang@mit.edu> writes:

> In the copy_process() routine called by _do_fork(), failure to allocate
> a PID (or further along in the function) will trigger an invocation to
> exit_thread(). This is done to clean up from an earlier call to
> copy_thread_tls(). Naturally, the child task is passed into exit_thread(),
> however during the process, io_bitmap_exit() nullifies the parent's
> io_bitmap rather than the child's.
>
> As copy_thread_tls() has been called ahead of the failure, the reference
> count on the calling thread's io_bitmap is incremented as we would expect.
> However, io_bitmap_exit() doesn't accept any arguments, and thus assumes
> it should trash the current thread's io_bitmap reference rather than the
> child's. This is pretty sneaky in practice, because in all instances but
> this one, exit_thread() is called with respect to the current task and
> everything works out.
>
> A determined attacker can issue an appropriate ioctl (i.e. KDENABIO) to
> get a bitmap allocated, and force a clone3() syscall to fail by passing
> in a zeroed clone_args structure. The kernel handles the erroneous struct
> and the buggy code path is followed, and even though the parent's reference
> to the io_bitmap is trashed, the child still holds a reference and thus
> the structure will never be freed.

Nice catch! I'm sure I thought about that at some point and then forgot
again.

> Fix this by tweaking io_bitmap_exit() and its subroutines to accept a
> task_struct argument which to operate on.

> This may not be the most elegant solution, but it mitigates the
> trigger described above on an x86_64 kernel.

It's well done and straight forward and comes with a well done change
log. Appreciated!

Thanks,

tglx

\
 
 \ /
  Last update: 2020-05-28 21:33    [W:0.055 / U:0.672 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site