On Thu, Dec 5, 2024 at 6:01 PM Rong Tao <rtoax@xxxxxxxxxxx> 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>
> ---
> 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;
This is completely broken. Just because the names are different
doesn't mean that they don't point to the same file.
Fix the root cause of segfault instead.
pw-bot: cr
