From: Rong Tao <rongtao@xxxxxxxx> If the input file and output file are the same, the input file is cleared due to opening, resulting in a NULL pointer access by libbpf. $ 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@xxxxxxxx> --- v2: https://lore.kernel.org/lkml/tencent_F62A51AFF6A38188D70664421F5934974008@xxxxxx/ v1: https://lore.kernel.org/lkml/tencent_410B8166C55CD2AB64BDEA8E92204619180A@xxxxxx/ --- tools/bpf/bpftool/gen.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c index 5a4d3240689e..e5e3e8705cc7 100644 --- a/tools/bpf/bpftool/gen.c +++ b/tools/bpf/bpftool/gen.c @@ -1879,6 +1879,8 @@ static int do_object(int argc, char **argv) struct bpf_linker *linker; const char *output_file, *file; int err = 0; + int argc_cpy; + char **argv_cpy; if (!REQ_ARGS(2)) { usage(); @@ -1887,6 +1889,17 @@ static int do_object(int argc, char **argv) output_file = GET_ARG(); + argc_cpy = argc; + argv_cpy = argv; + + /* Ensure we don't overwrite any input file */ + while (argc_cpy--) { + if (!strcmp(output_file, *argv_cpy++)) { + p_err("Input and output files cannot be the same"); + goto out; + } + } + linker = bpf_linker__new(output_file, NULL); if (!linker) { p_err("failed to create BPF linker instance"); -- 2.47.1