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Commit 4e4c8540 authored by Piotr Krysiuk's avatar Piotr Krysiuk Committed by Greg Kroah-Hartman
Browse files

bpf: Add sanity check for upper ptr_limit 



commit 1b1597e64e1a610c7a96710fc4717158e98a08b3 upstream.

Given we know the max possible value of ptr_limit at the time of retrieving
the latter, add basic assertions, so that the verifier can bail out if
anything looks odd and reject the program. Nothing triggered this so far,
but it also does not hurt to have these.

Signed-off-by: default avatarPiotr Krysiuk <piotras@gmail.com>
Co-developed-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 524471df

kernel/bpf/verifier.c

+8 −3
Original line number Diff line number Diff line
@@ -4268,10 +4268,14 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, 
{

	bool mask_to_left = (opcode == BPF_ADD &&  off_is_neg) ||

			    (opcode == BPF_SUB && !off_is_neg);

	u32 off;

	u32 off, max;



	switch (ptr_reg->type) {

	case PTR_TO_STACK:

		/* Offset 0 is out-of-bounds, but acceptable start for the

		 * left direction, see BPF_REG_FP.

		 */

		max = MAX_BPF_STACK + mask_to_left;

		/* Indirect variable offset stack access is prohibited in

		 * unprivileged mode so it's not handled here.

		 */
@@ -4280,15 +4284,16 @@ static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, 
			*ptr_limit = MAX_BPF_STACK + off;

		else

			*ptr_limit = -off - 1;

		return 0;

		return *ptr_limit >= max ? -ERANGE : 0;

	case PTR_TO_MAP_VALUE:

		max = ptr_reg->map_ptr->value_size;

		if (mask_to_left) {

			*ptr_limit = ptr_reg->umax_value + ptr_reg->off;

		} else {

			off = ptr_reg->smin_value + ptr_reg->off;

			*ptr_limit = ptr_reg->map_ptr->value_size - off - 1;

		}

		return 0;

		return *ptr_limit >= max ? -ERANGE : 0;

	default:

		return -EINVAL;

	}