From: "Daniel T. Lee" <danieltimlee@gmail.com>
Date: Fri, 10 Apr 2020 11:06:12 +0900
Subject: tools, bpftool: Fix struct_ops command invalid pointer free
Patch-mainline: v5.7-rc2
Git-commit: 96b2eb6e77959b4b52f80e7a61d03db77606aac6
References: bsc#1177028

In commit 65c93628599d ("bpftool: Add struct_ops support") a new
type of command named struct_ops has been added. This command requires
a kernel with CONFIG_DEBUG_INFO_BTF=y set and for retrieving BTF info
in bpftool, the helper get_btf_vmlinux() is used.

When running this command on kernel without BTF debug info, this will
lead to 'btf_vmlinux' variable being an 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.

Fixes: 65c93628599d ("bpftool: Add struct_ops support")
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200410020612.2930667-1-danieltimlee@gmail.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/bpf/bpftool/struct_ops.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- 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;
 }