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[209.85.219.172]) by smtp.gmail.com with ESMTPSA id 200-v6sm6244113ywq.97.2018.11.13.12.16.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 13 Nov 2018 12:16:30 -0800 (PST) Received: by mail-yb1-f172.google.com with SMTP id g192-v6so5954330ybf.3 for ; Tue, 13 Nov 2018 12:16:30 -0800 (PST) X-Received: by 2002:a25:3588:: with SMTP id c130-v6mr6525056yba.410.1542140189975; Tue, 13 Nov 2018 12:16:29 -0800 (PST) MIME-Version: 1.0 Received: by 2002:a25:b906:0:0:0:0:0 with HTTP; Tue, 13 Nov 2018 12:16:29 -0800 (PST) In-Reply-To: <20181112160931.GA28463@redhat.com> References: <20181112160931.GA28463@redhat.com> From: Kees Cook Date: Tue, 13 Nov 2018 14:16:29 -0600 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] exec: load_script: don't blindly truncate shebang string To: Oleg Nesterov Cc: Andrew Morton , Ben Woodard , "Eric W. Biederman" , Michal Hocko , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 12, 2018 at 10:09 AM, Oleg Nesterov 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 Acked-by: Kees Cook -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