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=8ebf179a95c2a2670f7cf1ba62429ec044369db... 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