Commit f2bcd05e authored Apr 03, 2019 by Andrey Ignatov Committed by Daniel Borkmann Apr 05, 2019

bpf: Reject indirect var_off stack access in raw mode



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: 2011fccf ("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>

parent 636e78b1

kernel/bpf/verifier.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -2226,6 +2226,15 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
		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,

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