On 05/12/2024 11:10, Rong Tao wrote: > 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> > --- > v1: https://lore.kernel.org/lkml/tencent_410B8166C55CD2AB64BDEA8E92204619180A@xxxxxx/ > --- > tools/bpf/bpftool/gen.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c > index 5a4d3240689e..506d205138db 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 = argc; > + char **argv_cpy = argv; Oops sorry, argc_cpy and argv_cpy need to be initialised _after_ the call to GET_ARG() below, otherwise we always start comparing output_file with itself. Please test this code on your side, too :) pw-bot: cr > > if (!REQ_ARGS(2)) { > usage(); > @@ -1887,6 +1889,14 @@ static int do_object(int argc, char **argv) > > output_file = GET_ARG(); > > + /* 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");
