From: Piotr Krysiuk Date: Tue, 16 Mar 2021 08:47:02 +0000 (+0100) Subject: bpf: Add sanity check for upper ptr_limit X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=1b1597e64e1a610c7a96710fc4717158e98a08b3;p=linux.git bpf: Add sanity check for upper ptr_limit 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 Co-developed-by: Daniel Borkmann Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov --- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d16722a99b61d..44e4ec1640f1d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5861,10 +5861,14 @@ 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. */ @@ -5873,15 +5877,16 @@ 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; }