From: Jann Horn jannh@google.com
commit 8ff3571f7e1bf3f293cc5e3dc14f2943f4fa7fcf upstream.
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 Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20200417000007.10734-2-jannh@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2885,7 +2885,7 @@ static int check_ptr_to_btf_access(struc 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;