This is a note to let you know that I've just added the patch titled
bpf: Add sanity check for upper ptr_limit
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-add-sanity-check-for-upper-ptr_limit.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1b1597e64e1a610c7a96710fc4717158e98a08b3 Mon Sep 17 00:00:00 2001
From: Piotr Krysiuk <piotras@xxxxxxxxx>
Date: Tue, 16 Mar 2021 09:47:02 +0100
Subject: bpf: Add sanity check for upper ptr_limit
From: Piotr Krysiuk <piotras@xxxxxxxxx>
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: Piotr Krysiuk <piotras@xxxxxxxxx>
Co-developed-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/bpf/verifier.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2029,24 +2029,29 @@ static int retrieve_ptr_limit(const stru
{
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;
off = ptr_reg->off + ptr_reg->var_off.value;
if (mask_to_left)
*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;
}
Patches currently in stable-queue which might be from piotras@xxxxxxxxx are
queue-4.14/bpf-fix-off-by-one-for-area-size-in-creating-mask-to-left.patch
queue-4.14/bpf-simplify-alu_limit-masking-for-pointer-arithmetic.patch
queue-4.14/bpf-add-sanity-check-for-upper-ptr_limit.patch
