linux-kernel - [PATCH] exec/binfmt_script: trip zero bytes from the buffer

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Message-Id: <20210615162346.16032-1-avagin@gmail.com>
Date:   Tue, 15 Jun 2021 09:23:46 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        linux-fsdevel@...r.kernel.org, Andrei Vagin <avagin@...il.com>
Subject: [PATCH] exec/binfmt_script: trip zero bytes from the buffer

Without this fix, if we try to run a script that contains only the
interpreter line, the interpreter is executed with one extra empty
argument.

The code is written so that i_end has to be set to the end of valuable
data in the buffer.

Fixes: ccbb18b67323 ("exec/binfmt_script: Don't modify bprm->buf and then return -ENOEXEC")
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Andrei Vagin <avagin@...il.com>
---
 fs/binfmt_script.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index 1b6625e95958..e242680f96e1 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -68,6 +68,9 @@ static int load_script(struct linux_binprm *bprm)
 		if (!next_terminator(i_end, buf_end))
 			return -ENOEXEC;
 		i_end = buf_end;
+		/* Trim zero bytes from i_end */
+		while (i_end[-1] == 0)
+			i_end--;
 	}
 	/* Trim any trailing spaces/tabs from i_end */
 	while (spacetab(i_end[-1]))
-- 
2.31.1