lkml.org 
[lkml]   [2021]   [May]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] Revert "ACPI: custom_method: fix memory leaks"
    On Mon, May 03, 2021 at 08:17:14AM -0500, Mark Langsdorf wrote:
    > In 5/2/21 12:23 PM, Kees Cook wrote:
    > > This reverts commit 03d1571d9513369c17e6848476763ebbd10ec2cb.
    > >
    > > While /sys/kernel/debug/acpi/custom_method is already a privileged-only
    > > API providing proxied arbitrary write access to kernel memory[1][2],
    > > with existing race conditions[3] in buffer allocation and use that could
    > > lead to memory leaks and use-after-free conditions, the above commit
    > > appears to accidentally make the use-after-free conditions even easier
    > > to accomplish. ("buf" is a global variable and prior kfree()s would set
    > > buf back to NULL.)
    > >
    > > This entire interface needs to be reworked (if not entirely removed).
    > >
    > > [1] https://lore.kernel.org/lkml/20110222193250.GA23913@outflux.net/
    > > [2] https://lore.kernel.org/lkml/201906221659.B618D83@keescook/
    > > [3] https://lore.kernel.org/lkml/20170109231323.GA89642@beast/
    > >
    > > Cc: Wenwen Wang <wenwen@cs.uga.edu>
    > > Signed-off-by: Kees Cook <keescook@chromium.org>
    > > ---
    >
    > I have two patches submitted to linux-acpi to fix the most obvious bugs in
    > the current driver.  I don't think that just reverting this patch in its
    > entirety is a good solution: it still leaves the buf allocated in -EINVAL,
    > as well as the weird case where a not fully consumed buffer can be
    > reallocated without being freed on a subsequent call.
    >
    > https://lore.kernel.org/linux-acpi/20210427185434.34885-1-mlangsdo@redhat.com/
    >
    > https://lore.kernel.org/linux-acpi/20210423152818.97077-1-mlangsdo@redhat.com/
    >
    > I support rewriting this driver in its entirety, but reverting one bad patch
    > to leave it in a different buggy state is less than ideal.

    Thanks for working on that! It'd be nice if there was a lock held for
    the duration of the "open", then all the concurrency races would go
    away. But, I haven't spent a lot of time looking since it's root-only
    and already blocked by lockdown, etc.

    --
    Kees Cook

    \
     
     \ /
      Last update: 2021-05-03 20:36    [W:2.435 / U:0.616 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site