exec: load_script: don't blindly truncate shebang string
[ Upstream commit 8099b047ecc431518b9bb6bdbba3549bbecdc343 ]
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.
Link: http://lkml.kernel.org/r/20181112160931.GA28463@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Ben Woodard <woodard@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index afdf4e3..634bdbb 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -43,10 +43,14 @@
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'))