From: Oleg Nesterov <oleg@xxxxxxxxxx> [ 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@xxxxxxxxxx Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Ben Woodard <woodard@xxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 5027a3e14922..f62e45df2d38 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -33,10 +33,14 @@ 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')) -- 2.19.1
