From: Quentin Monnet <qmo@kernel.org> mainline inclusion from mainline-v6.14-rc1 commit e10500b69c3f3378f3dcfc8c2fe4cdb74fc844f5 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBR43L Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- Libelf functions do not set errno on failure. Instead, it relies on its internal _elf_errno value, that can be retrieved via elf_errno (or the corresponding message via elf_errmsg()). From "man libelf": If a libelf function encounters an error it will set an internal error code that can be retrieved with elf_errno. Each thread maintains its own separate error code. The meaning of each error code can be determined with elf_errmsg, which returns a string describing the error. As a consequence, libbpf should not return -errno when a function from libelf fails, because an empty value will not be interpreted as an error and won't prevent the program to stop. This is visible in bpf_linker__add_file(), for example, where we call a succession of functions that rely on libelf: 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); err = err ?: linker_append_elf_relos(linker, &obj); err = err ?: linker_append_btf(linker, &obj); err = err ?: linker_append_btf_ext(linker, &obj); If the object file that we try to process is not, in fact, a correct object file, linker_load_obj_file() may fail with errno not being set, and return 0. In this case we attempt to run linker_append_elf_sysms() and may segfault. This can happen (and was discovered) with bpftool: $ bpftool gen object output.o sample_ret0.bpf.c libbpf: failed to get ELF header for sample_ret0.bpf.c: invalid `Elf' handle zsh: segmentation fault (core dumped) bpftool gen object output.o sample_ret0.bpf.c Fix the issue by returning a non-null error code (-EINVAL) when libelf functions fail. Fixes: faf6ed321cf6 ("libbpf: Add BPF static linker APIs") Signed-off-by: Quentin Monnet <qmo@kernel.org> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20241205135942.65262-1-qmo@kernel.org Signed-off-by: Xiaomeng Zhang <zhangxiaomeng13@huawei.com> --- tools/lib/bpf/linker.c | 22 ++++++++-------------- 1 file changed, 8 insertions(+), 14 deletions(-) diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index 88cc7236f122..736ebceea233 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -567,17 +567,15 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, } obj->elf = elf_begin(obj->fd, ELF_C_READ_MMAP, NULL); if (!obj->elf) { - err = -errno; pr_warn_elf("failed to parse ELF file '%s'", filename); - return err; + return -EINVAL; } /* Sanity check ELF file high-level properties */ ehdr = elf64_getehdr(obj->elf); if (!ehdr) { - err = -errno; pr_warn_elf("failed to get ELF header for %s", filename); - return err; + return -EINVAL; } if (ehdr->e_ident[EI_DATA] != host_endianness) { err = -EOPNOTSUPP; @@ -593,9 +591,8 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, } if (elf_getshdrstrndx(obj->elf, &obj->shstrs_sec_idx)) { - err = -errno; pr_warn_elf("failed to get SHSTRTAB section index for %s", filename); - return err; + return -EINVAL; } scn = NULL; @@ -605,26 +602,23 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename, shdr = elf64_getshdr(scn); if (!shdr) { - err = -errno; pr_warn_elf("failed to get section #%zu header for %s", sec_idx, filename); - return err; + return -EINVAL; } sec_name = elf_strptr(obj->elf, obj->shstrs_sec_idx, shdr->sh_name); if (!sec_name) { - err = -errno; pr_warn_elf("failed to get section #%zu name for %s", sec_idx, filename); - return err; + return -EINVAL; } data = elf_getdata(scn, 0); if (!data) { - err = -errno; pr_warn_elf("failed to get section #%zu (%s) data from %s", sec_idx, sec_name, filename); - return err; + return -EINVAL; } sec = add_src_sec(obj, sec_name); @@ -2602,14 +2596,14 @@ int bpf_linker__finalize(struct bpf_linker *linker) /* Finalize ELF layout */ if (elf_update(linker->elf, ELF_C_NULL) < 0) { - err = -errno; + err = -EINVAL; pr_warn_elf("failed to finalize ELF layout"); return libbpf_err(err); } /* Write out final ELF contents */ if (elf_update(linker->elf, ELF_C_WRITE) < 0) { - err = -errno; + err = -EINVAL; pr_warn_elf("failed to write ELF contents"); return libbpf_err(err); } -- 2.34.1