On 12/5/24 19:20, Quentin Monnet wrote:
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
Sorry, i just test this patch in [1], and it's works, maybe the
compile-flags is differenet.
I'll fix this and submit v2 soon, thanks!!
[1] https://github.com/libbpf/bpftool
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");
