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Date: Mon, 28 Jan 2019 10:59:22 -0500 From: Sasha Levin <sashal@...nel.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: Oleg Nesterov <oleg@...hat.com>, Ben Woodard <woodard@...hat.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Sasha Levin <sashal@...nel.org>, linux-fsdevel@...r.kernel.org Subject: [PATCH AUTOSEL 4.19 256/258] exec: load_script: don't blindly truncate shebang string From: Oleg Nesterov <oleg@...hat.com> [ 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@...hat.com> Acked-by: Kees Cook <keescook@...omium.org> Acked-by: Michal Hocko <mhocko@...e.com> Cc: Ben Woodard <woodard@...hat.com> Cc: "Eric W. Biederman" <ebiederm@...ssion.com> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> Signed-off-by: Sasha Levin <sashal@...nel.org> --- 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 7cde3f46ad26..d0078cbb718b 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')) -- 2.19.1
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