On Mon, Nov 12, 2018 at 10:09 AM, Oleg Nesterov <o...@redhat.com> wrote: > load_script() simply truncates bprm->buf and this is very wrong if the > length of shebang string exceeds BINPRM_BUF_SIZE-2. This can silently > truncate i_arg or (worse) we can execute the wrong binary if buf[2:126] > happens to be the valid executable path. > > Change load_script() to return ENOEXEC if it can't find '\n' or zero in > bprm->buf. Note that '\0' can come from either prepare_binprm()->memset() > or from kernel_read(), we do not care. > > Signed-off-by: Oleg Nesterov <o...@redhat.com>
Acked-by: Kees Cook <keesc...@chromium.org> -Kees > --- > fs/binfmt_script.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c > index 7cde3f4..d0078cb 100644 > --- a/fs/binfmt_script.c > +++ b/fs/binfmt_script.c > @@ -42,10 +42,14 @@ static int load_script(struct linux_binprm *bprm) > fput(bprm->file); > bprm->file = NULL; > > - bprm->buf[BINPRM_BUF_SIZE - 1] = '\0'; > - if ((cp = strchr(bprm->buf, '\n')) == NULL) > - cp = bprm->buf+BINPRM_BUF_SIZE-1; > + for (cp = bprm->buf+2;; cp++) { > + if (cp >= bprm->buf + BINPRM_BUF_SIZE) > + return -ENOEXEC; > + if (!*cp || (*cp == '\n')) > + break; > + } > *cp = '\0'; > + > while (cp > bprm->buf) { > cp--; > if ((*cp == ' ') || (*cp == '\t')) > -- > 2.5.0 > > -- Kees Cook