bpf: Add sanity check for upper ptr_limit

Origin: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit?id=1b1597e64e1a610c7a96710fc4717158e98a08b3

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@gmail.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name bpf-Add-sanity-check-for-upper-ptr_limit.patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e6b238a5e785dff992cf1fb6bb743c6dd747e466..9a1aba2d007334b8e1dc87d3e8eef0c444f1f923 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5333,10 +5333,14 @@ 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.
                 */
@@ -5345,15 +5349,16 @@ 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;
        }