From: Daniel Borkmann Date: Fri, 28 May 2021 10:38:09 +0000 (+0300) Subject: bpf: Fix mask direction swap upon off reg sign change X-Git-Tag: v4.19.193~59 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=9324bd041d5c0a9c41238d390838778b9387030e;p=thirdparty%2Fkernel%2Fstable.git bpf: Fix mask direction swap upon off reg sign change commit bb01a1bba579b4b1c5566af24d95f1767859771e upstream Masking direction as indicated via mask_to_left is considered to be calculated once and then used to derive pointer limits. Thus, this needs to be placed into bpf_sanitize_info instead so we can pass it to sanitize_ptr_alu() call after the pointer move. Piotr noticed a corner case where the off reg causes masking direction change which then results in an incorrect final aux->alu_limit. Fixes: 7fedb63a8307 ("bpf: Tighten speculative pointer arithmetic mask") Reported-by: Piotr Krysiuk Signed-off-by: Daniel Borkmann Reviewed-by: Piotr Krysiuk Acked-by: Alexei Starovoitov Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 0066ea8ecdaa9..a235342507a89 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2738,18 +2738,10 @@ enum { }; static int retrieve_ptr_limit(const struct bpf_reg_state *ptr_reg, - const struct bpf_reg_state *off_reg, - u32 *alu_limit, u8 opcode) + u32 *alu_limit, bool mask_to_left) { - bool off_is_neg = off_reg->smin_value < 0; - bool mask_to_left = (opcode == BPF_ADD && off_is_neg) || - (opcode == BPF_SUB && !off_is_neg); u32 max = 0, ptr_limit = 0; - if (!tnum_is_const(off_reg->var_off) && - (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) - return REASON_BOUNDS; - switch (ptr_reg->type) { case PTR_TO_STACK: /* Offset 0 is out-of-bounds, but acceptable start for the @@ -2817,6 +2809,7 @@ static bool sanitize_needed(u8 opcode) struct bpf_sanitize_info { struct bpf_insn_aux_data aux; + bool mask_to_left; }; static int sanitize_ptr_alu(struct bpf_verifier_env *env, @@ -2848,7 +2841,16 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, if (vstate->speculative) goto do_sim; - err = retrieve_ptr_limit(ptr_reg, off_reg, &alu_limit, opcode); + if (!commit_window) { + if (!tnum_is_const(off_reg->var_off) && + (off_reg->smin_value < 0) != (off_reg->smax_value < 0)) + return REASON_BOUNDS; + + info->mask_to_left = (opcode == BPF_ADD && off_is_neg) || + (opcode == BPF_SUB && !off_is_neg); + } + + err = retrieve_ptr_limit(ptr_reg, &alu_limit, info->mask_to_left); if (err < 0) return err;