netdev - [PATCH bpf-next 1/2] bpf: fix kallsyms handling for subprogs

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Date:   Wed, 20 Dec 2017 13:42:56 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     alexei.starovoitov@...il.com
Cc:     netdev@...r.kernel.org, jakub.kicinski@...ronome.com,
        quentin.monnet@...ronome.com,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf-next 1/2] bpf: fix kallsyms handling for subprogs

Right now kallsyms handling is not working with JITed subprogs.
The reason is that when in 1c2a088a6626 ("bpf: x64: add JIT support
for multi-function programs") in jit_subprogs() they are passed
to bpf_prog_kallsyms_add(), then their prog type is 0, which BPF
core will think it's a cBPF program as only cBPF programs have a
0 type. Thus, they need to inherit the type from the main prog.

Once that is fixed, they are indeed added to the BPF kallsyms
infra, but their tag is 0. Therefore, since intention is to add
them as bpf_prog_F_<tag>, we need to pass them to bpf_prog_calc_tag()
first. And once this is resolved, there is a use-after-free on
prog cleanup: we remove the kallsyms entry from the main prog,
later walk all subprogs and call bpf_jit_free() on them. However,
the kallsyms linkage was never released on them. Thus, do that
for all subprogs right in __bpf_prog_put() when refcount hits 0.

Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs")
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Alexei Starovoitov <ast@...nel.org>
---
 kernel/bpf/syscall.c  | 6 ++++++
 kernel/bpf/verifier.c | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e2e1c78..30e728d 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -937,10 +937,16 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu)
 static void __bpf_prog_put(struct bpf_prog *prog, bool do_idr_lock)
 {
 	if (atomic_dec_and_test(&prog->aux->refcnt)) {
+		int i;
+
 		trace_bpf_prog_put_rcu(prog);
 		/* bpf_prog_free_id() must be called first */
 		bpf_prog_free_id(prog, do_idr_lock);
+
+		for (i = 0; i < prog->aux->func_cnt; i++)
+			bpf_prog_kallsyms_del(prog->aux->func[i]);
 		bpf_prog_kallsyms_del(prog);
+
 		call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu);
 	}
 }
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 48b2901..811e6e9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5062,7 +5062,10 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 			goto out_free;
 		memcpy(func[i]->insnsi, &prog->insnsi[subprog_start],
 		       len * sizeof(struct bpf_insn));
+		func[i]->type = prog->type;
 		func[i]->len = len;
+		if (bpf_prog_calc_tag(func[i]))
+			goto out_free;
 		func[i]->is_func = 1;
 		/* Use bpf_prog_F_tag to indicate functions in stack traces.
 		 * Long term would need debug info to populate names
-- 
2.9.5