From: Andrey Ignatov rdna@fb.com
commit f2bcd05ec7b839ff826d2008506ad2d2dff46a59 upstream.
It's hard to guarantee that whole memory is marked as initialized on helper return if uninitialized stack is accessed with variable offset since specific bounds are unknown to verifier. This may cause uninitialized stack leaking.
Reject such an access in check_stack_boundary to prevent possible leaking.
There are no known use-cases for indirect uninitialized stack access with variable offset so it shouldn't break anything.
Fixes: 2011fccfb61b ("bpf: Support variable offset stack access from helpers") Reported-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Andrey Ignatov rdna@fb.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/verifier.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1811,6 +1811,15 @@ static int check_stack_boundary(struct b if (err) return err; } else { + /* Only initialized buffer on stack is allowed to be accessed + * with variable offset. With uninitialized buffer it's hard to + * guarantee that whole memory is marked as initialized on + * helper return since specific bounds are unknown what may + * cause uninitialized stack leaking. + */ + if (meta && meta->raw_mode) + meta = NULL; + min_off = reg->smin_value + reg->off; max_off = reg->umax_value + reg->off; err = __check_stack_boundary(env, regno, min_off, access_size,