Re: [PATCH 5.10] bpf: Fix KASAN use-after-free Read in compute_effective_progs

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Aug 20, 2022 at 01:05:18PM +0800, Pu Lehui wrote:
> From: Tadeusz Struk <tadeusz.struk@linaro.org>
> 
> commit 4c46091ee985ae84c60c5e95055d779fcd291d87 upstream.
> 
> Syzbot found a Use After Free bug in compute_effective_progs().
> The reproducer creates a number of BPF links, and causes a fault
> injected alloc to fail, while calling bpf_link_detach on them.
> Link detach triggers the link to be freed by bpf_link_free(),
> which calls __cgroup_bpf_detach() and update_effective_progs().
> If the memory allocation in this function fails, the function restores
> the pointer to the bpf_cgroup_link on the cgroup list, but the memory
> gets freed just after it returns. After this, every subsequent call to
> update_effective_progs() causes this already deallocated pointer to be
> dereferenced in prog_list_length(), and triggers KASAN UAF error.
> 
> To fix this issue don't preserve the pointer to the prog or link in the
> list, but remove it and replace it with a dummy prog without shrinking
> the table. The subsequent call to __cgroup_bpf_detach() or
> __cgroup_bpf_detach() will correct it.
> 
> Fixes: af6eea57437a ("bpf: Implement bpf_link-based cgroup BPF program attachment")
> Reported-by: <syzbot+f264bffdfbd5614f3bb2@syzkaller.appspotmail.com>
> Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> Cc: <stable@vger.kernel.org>
> Link: https://syzkaller.appspot.com/bug?id=8ebf179a95c2a2670f7cf1ba62429ec044369db4
> Link: https://lore.kernel.org/bpf/20220517180420.87954-1-tadeusz.struk@linaro.org
> Signed-off-by: Pu Lehui <pulehui@huawei.com>
> ---
>  kernel/bpf/cgroup.c | 70 ++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 60 insertions(+), 10 deletions(-)

Now queued up, thanks.

greg k-h