| Message ID | 20200417000007.10734-2-jannh@google.com |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [v2,1/2] bpf: Forbid XADD on spilled pointers for unprivileged users | expand |
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9e92d3d5ffd17..9382609147f53 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3099,7 +3099,7 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, if (ret < 0) return ret; - if (atype == BPF_READ) { + if (atype == BPF_READ && value_regno >= 0) { if (ret == SCALAR_VALUE) { mark_reg_unknown(env, regs, value_regno); return 0;
check_xadd() can cause check_ptr_to_btf_access() to be executed with atype==BPF_READ and value_regno==-1 (meaning "just check whether the access is okay, don't tell me what type it will result in"). Handle that case properly and skip writing type information, instead of indexing into the registers at index -1 and writing into out-of-bounds memory. Note that at least at the moment, you can't actually write through a BTF pointer, so check_xadd() will reject the program after calling check_ptr_to_btf_access with atype==BPF_WRITE; but that's after the verifier has already corrupted memory. This patch assumes that BTF pointers are not available in unprivileged programs. Fixes: 9e15db66136a ("bpf: Implement accurate raw_tp context access via BTF") Signed-off-by: Jann Horn <jannh@google.com> --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)