netdev - [PATCH] tools: bpftool: fix struct_ops command invalid pointer free

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Date:   Fri, 10 Apr 2020 11:06:12 +0900
From:   "Daniel T. Lee" <danieltimlee@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>
Subject: [PATCH] tools: bpftool: fix struct_ops command invalid pointer free

>From commit 65c93628599d ("bpftool: Add struct_ops support"),
a new type of command struct_ops has been added.

This command requires kernel CONFIG_DEBUG_INFO_BTF=y, and for retrieving
btf info, get_btf_vmlinux() is used.

When running this command on kernel without BTF debug info, this will
lead to 'btf_vmlinux' variable contains invalid(error) pointer. And by
this, btf_free() causes a segfault when executing 'bpftool struct_ops'.

This commit adds pointer validation with IS_ERR not to free invalid
pointer, and this will fix the segfault issue.

Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
---
 tools/bpf/bpftool/struct_ops.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/struct_ops.c b/tools/bpf/bpftool/struct_ops.c
index 2a7befbd11ad..0fe0d584c57e 100644
--- a/tools/bpf/bpftool/struct_ops.c
+++ b/tools/bpf/bpftool/struct_ops.c
@@ -591,6 +591,8 @@ int do_struct_ops(int argc, char **argv)
 
 	err = cmd_select(cmds, argc, argv, do_help);
 
-	btf__free(btf_vmlinux);
+	if (!IS_ERR(btf_vmlinux))
+		btf__free(btf_vmlinux);
+
 	return err;
 }
-- 
2.26.0