linux-kernel - [PATCH bpf-next v4 2/2] libbpf: linker: Avoid using object file as both input and output

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Message-ID: <tencent_4C02217218D4082166DD5C52A8D8BF228F0A@qq.com>
Date: Fri,  6 Dec 2024 10:01:34 +0800
From: Rong Tao <rtoax@...mail.com>
To: andrii.nakryiko@...il.com,
	qmo@...nel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	rongtao@...tc.cn
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	bpf@...r.kernel.org (open list:BPF [TOOLING] (bpftool)),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH bpf-next v4 2/2] libbpf: linker: Avoid using object file as both input and output

From: Rong Tao <rongtao@...tc.cn>

When the target file is used as input and output at the same time, the
input file will read a null value, resulting in a segmentation fault.

    $ bpftool gen object prog.o prog.o
    libbpf: failed to get ELF header for prog.o: invalid `Elf' handle
    Segmentation fault

    (gdb) bt
    #0  0x0000000000450285 in linker_append_elf_syms (linker=0x4feda0, obj=0x7fffffffe100) at linker.c:1296
    #1  bpf_linker__add_file (linker=0x4feda0, filename=<optimized out>, opts=<optimized out>) at linker.c:453
    #2  0x000000000040c235 in do_object ()
    #3  0x00000000004021d7 in main ()
    (gdb) frame 0
    #0  0x0000000000450285 in linker_append_elf_syms (linker=0x4feda0, obj=0x7fffffffe100) at linker.c:1296
    1296                Elf64_Sym *sym = symtab->data->d_buf;

Signed-off-by: Rong Tao <rongtao@...tc.cn>
---
 tools/lib/bpf/linker.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index cf71d149fe26..0b117cc5b6e4 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -448,6 +448,11 @@ int bpf_linker__add_file(struct bpf_linker *linker, const char *filename,
 	if (!linker->elf)
 		return libbpf_err(-EINVAL);
 
+	if (!strcmp(filename, linker->filename)) {
+		pr_warn_elf("Input and output files cannot be the same");
+		return libbpf_err(-EINVAL);
+	}
+
 	err = err ?: linker_load_obj_file(linker, filename, opts, &obj);
 	err = err ?: linker_append_sec_data(linker, &obj);
 	err = err ?: linker_append_elf_syms(linker, &obj);
-- 
2.47.1