From: Ariadne Conill <ariadne@dereferenced.org>
To: linux-kernel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org,
Eric Biederman <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Ariadne Conill <ariadne@dereferenced.org>
Subject: [PATCH v2] fs/exec: require argv[0] presence in do_execveat_common()
Date: Wed, 26 Jan 2022 11:44:47 +0000 [thread overview]
Message-ID: <20220126114447.25776-1-ariadne@dereferenced.org> (raw)
In several other operating systems, it is a hard requirement that the
first argument to execve(2) be the name of a program, thus prohibiting
a scenario where argc < 1. POSIX 2017 also recommends this behaviour,
but it is not an explicit requirement[0]:
The argument arg0 should point to a filename string that is
associated with the process being started by one of the exec
functions.
To ensure that execve(2) with argc < 1 is not a useful gadget for
shellcode to use, we can validate this in do_execveat_common() and
fail for this scenario, effectively blocking successful exploitation
of CVE-2021-4034 and similar bugs which depend on this gadget.
The use of -EFAULT for this case is similar to other systems, such
as FreeBSD, OpenBSD and Solaris. QNX uses -EINVAL for this case.
Interestingly, Michael Kerrisk opened an issue about this in 2008[1],
but there was no consensus to support fixing this issue then.
Hopefully now that CVE-2021-4034 shows practical exploitative use
of this bug in a shellcode, we can reconsider.
[0]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html
[1]: https://bugzilla.kernel.org/show_bug.cgi?id=8408
Changes from v1:
- Rework commit message significantly.
- Make the argv[0] check explicit rather than hijacking the error-check
for count().
Signed-off-by: Ariadne Conill <ariadne@dereferenced.org>
---
fs/exec.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/exec.c b/fs/exec.c
index 79f2c9483302..e52c41991aab 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1899,6 +1899,10 @@ static int do_execveat_common(int fd, struct filename *filename,
retval = count(argv, MAX_ARG_STRINGS);
if (retval < 0)
goto out_free;
+ if (retval == 0) {
+ retval = -EFAULT;
+ goto out_free;
+ }
bprm->argc = retval;
retval = count(envp, MAX_ARG_STRINGS);
--
2.34.1
next reply other threads:[~2022-01-26 11:44 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 11:44 Ariadne Conill [this message]
2022-01-26 14:40 ` [PATCH v2] fs/exec: require argv[0] presence in do_execveat_common() Matthew Wilcox
2022-01-26 17:41 ` Ariadne Conill
2022-01-26 14:59 ` Matthew Wilcox
2022-01-26 16:40 ` Kees Cook
2022-01-26 16:57 ` Eric W. Biederman
2022-01-26 17:32 ` Ariadne Conill
2022-01-26 18:03 ` Matthew Wilcox
2022-01-26 18:38 ` Ariadne Conill
2022-01-26 20:09 ` Kees Cook
2022-01-26 20:23 ` Ariadne Conill
2022-01-26 20:56 ` Kees Cook
2022-01-26 21:13 ` Ariadne Conill
2022-01-26 21:25 ` Kees Cook
2022-01-26 21:30 ` Ariadne Conill
2022-01-26 22:49 ` Kees Cook
2022-01-26 23:07 ` Ariadne Conill
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