Messages in this thread | | | Subject | Re: [PATCH] Revert "ACPI: custom_method: fix memory leaks" | From | Mark Langsdorf <> | Date | Mon, 3 May 2021 08:17:14 -0500 |
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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.
--Mark Langsdorf
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