From: Alexei Starovoitov <ast@fb.com>
Date: Tue, 30 May 2017 13:31:30 -0700
Subject: bpf: reconcile bpf_tail_call and stack_depth
Patch-mainline: v4.13-rc1
Git-commit: 80a58d02559465b0ea403ff91c8bca9a733b1b0d
References: bsc#1056787

The next set of patches will take advantage of stack_depth tracking,
so make sure that the program that does bpf_tail_call() has
stack depth large enough for the callee.
We could have tracked the stack depth of the prog_array owner program
and only allow insertion of the programs with stack depth less
than the owner, but it will break existing applications.
Some of them have trivial root bpf program that only does
multiple bpf_tail_calls and at init time the prog array is empty.
In the future we may add a flag to do such tracking optionally,
but for now play simple and safe.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/verifier.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3626,6 +3626,7 @@ static int fixup_bpf_calls(struct bpf_ve
 			 * the program array.
 			 */
 			prog->cb_access = 1;
+			env->prog->aux->stack_depth = MAX_BPF_STACK;
 
 			/* mark bpf_tail_call as different opcode to avoid
 			 * conditional branch in the interpeter for every normal