From: "Mickaël Salaün" <mic@digikod.net>
To: "Eric W. Biederman" <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, "Aleksa Sarai" <cyphar@cyphar.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Christian Heimes" <christian@python.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Deven Bowers" <deven.desai@linux.microsoft.com>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Eric Biggers" <ebiggers@kernel.org>,
"Eric Chiang" <ericchiang@google.com>,
"Florian Weimer" <fweimer@redhat.com>,
"James Morris" <jmorris@namei.org>, "Jan Kara" <jack@suse.cz>,
"Jann Horn" <jannh@google.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Lakshmi Ramasubramanian" <nramas@linux.microsoft.com>,
"Matthew Garrett" <mjg59@google.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Michael Kerrisk" <mtk.manpages@gmail.com>,
"Mimi Zohar" <zohar@linux.ibm.com>,
"Philippe Trébuchet" <philippe.trebuchet@ssi.gouv.fr>,
"Scott Shell" <scottsh@microsoft.com>,
"Sean Christopherson" <sean.j.christopherson@intel.com>,
"Shuah Khan" <shuah@kernel.org>,
"Steve Dower" <steve.dower@python.org>,
"Steve Grubb" <sgrubb@redhat.com>,
"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
"Thibaut Sautereau" <thibaut.sautereau@clip-os.org>,
"Vincent Strubel" <vincent.strubel@ssi.gouv.fr>,
kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v7 3/7] exec: Move path_noexec() check earlier
Date: Thu, 13 Aug 2020 17:31:22 +0200 [thread overview]
Message-ID: <89b6bb7f-d841-cf0a-8d5c-26c611b56ae7@digikod.net> (raw)
In-Reply-To: <87a6z1m0u1.fsf@x220.int.ebiederm.org>
Kees Cook wrote this patch, which is in Andrew Morton's tree, but I
think you're talking about O_MAYEXEC, not this patch specifically.
On 11/08/2020 21:36, Eric W. Biederman wrote:
> Mickaël Salaün <mic@digikod.net> writes:
>
>> From: Kees Cook <keescook@chromium.org>
>>
>> The path_noexec() check, like the regular file check, was happening too
>> late, letting LSMs see impossible execve()s. Check it earlier as well
>> in may_open() and collect the redundant fs/exec.c path_noexec() test
>> under the same robustness comment as the S_ISREG() check.
>>
>> My notes on the call path, and related arguments, checks, etc:
>
> A big question arises, that I think someone already asked.
Al Viro and Jann Horn expressed such concerns for O_MAYEXEC:
https://lore.kernel.org/lkml/0cc94c91-afd3-27cd-b831-8ea16ca8ca93@digikod.net/
>
> Why perform this test in may_open directly instead of moving
> it into inode_permission. That way the code can be shared with
> faccessat, and any other code path that wants it?
This patch is just a refactoring.
About O_MAYEXEC, path-based LSM, IMA and IPE need to work on a struct
file, whereas inode_permission() only gives a struct inode. However,
faccessat2(2) (with extended flags) seems to be the perfect candidate if
we want to be able to check file descriptors.
>
> That would look to provide a more maintainable kernel.
Why would it be more maintainable?
>
> Eric
>
>
>> do_open_execat()
>> struct open_flags open_exec_flags = {
>> .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
>> .acc_mode = MAY_EXEC,
>> ...
>> do_filp_open(dfd, filename, open_flags)
>> path_openat(nameidata, open_flags, flags)
>> file = alloc_empty_file(open_flags, current_cred());
>> do_open(nameidata, file, open_flags)
>> may_open(path, acc_mode, open_flag)
>> /* new location of MAY_EXEC vs path_noexec() test */
>> inode_permission(inode, MAY_OPEN | acc_mode)
>> security_inode_permission(inode, acc_mode)
>> vfs_open(path, file)
>> do_dentry_open(file, path->dentry->d_inode, open)
>> security_file_open(f)
>> open()
>> /* old location of path_noexec() test */
>>
>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org
>> ---
>> fs/exec.c | 12 ++++--------
>> fs/namei.c | 4 ++++
>> 2 files changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/exec.c b/fs/exec.c
>> index bdc6a6eb5dce..4eea20c27b01 100644
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
>> * and check again at the very end too.
>> */
>> error = -EACCES;
>> - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
>> - goto exit;
>> -
>> - if (path_noexec(&file->f_path))
>> + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
>> + path_noexec(&file->f_path)))
>> goto exit;
>>
>> fsnotify_open(file);
>> @@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
>> * and check again at the very end too.
>> */
>> err = -EACCES;
>> - if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
>> - goto exit;
>> -
>> - if (path_noexec(&file->f_path))
>> + if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
>> + path_noexec(&file->f_path)))
>> goto exit;
>>
>> err = deny_write_access(file);
>> diff --git a/fs/namei.c b/fs/namei.c
>> index a559ad943970..ddc9b25540fe 100644
>> --- a/fs/namei.c
>> +++ b/fs/namei.c
>> @@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag)
>> return -EACCES;
>> flag &= ~O_TRUNC;
>> break;
>> + case S_IFREG:
>> + if ((acc_mode & MAY_EXEC) && path_noexec(path))
>> + return -EACCES;
>> + break;
>> }
>>
>> error = inode_permission(inode, MAY_OPEN | acc_mode);
next prev parent reply other threads:[~2020-08-13 15:31 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-23 17:12 [PATCH v7 0/7] Add support for O_MAYEXEC Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 1/7] exec: Change uselib(2) IS_SREG() failure to EACCES Mickaël Salaün
2020-08-11 18:59 ` Eric W. Biederman
2020-08-11 19:14 ` Eric W. Biederman
2020-07-23 17:12 ` [PATCH v7 2/7] exec: Move S_ISREG() check earlier Mickaël Salaün
2020-08-11 19:27 ` Eric W. Biederman
2020-07-23 17:12 ` [PATCH v7 3/7] exec: Move path_noexec() " Mickaël Salaün
2020-08-11 19:36 ` Eric W. Biederman
2020-08-13 15:31 ` Mickaël Salaün [this message]
2020-07-23 17:12 ` [PATCH v7 4/7] fs: Introduce O_MAYEXEC flag for openat2(2) Mickaël Salaün
2020-07-24 19:03 ` Kees Cook
2020-07-27 4:21 ` Al Viro
2020-07-27 5:27 ` Florian Weimer
2020-07-27 19:46 ` Mickaël Salaün
2020-08-11 19:51 ` Eric W. Biederman
2020-08-13 14:36 ` Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 5/7] fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2020-07-24 19:03 ` Kees Cook
2020-08-11 19:58 ` Eric W. Biederman
2020-08-13 14:49 ` Mickaël Salaün
2020-07-23 17:12 ` [PATCH v7 6/7] selftest/openat2: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2020-07-24 19:03 ` Kees Cook
2020-07-23 17:12 ` [PATCH v7 7/7] ima: add policy support for the new file open MAY_OPENEXEC flag Mickaël Salaün
2020-07-24 19:04 ` Kees Cook
2020-07-24 11:20 ` [PATCH v7 0/7] Add support for O_MAYEXEC Thibaut Sautereau
2020-07-24 19:06 ` Kees Cook
2020-07-25 11:15 ` Christian Brauner
2020-08-10 20:11 ` Mickaël Salaün
2020-08-10 20:21 ` Al Viro
2020-08-10 22:09 ` David Laight
2020-08-10 22:28 ` Al Viro
2020-08-10 22:47 ` Mickaël Salaün
2020-08-11 8:09 ` David Laight
2020-08-11 8:50 ` Mickaël Salaün
2020-08-10 22:43 ` Mickaël Salaün
2020-08-10 23:03 ` Jann Horn
2020-08-11 8:48 ` Mickaël Salaün
2020-08-11 13:56 ` Mimi Zohar
2020-08-11 14:02 ` Matthew Wilcox
2020-08-11 14:30 ` Mimi Zohar
2020-08-11 17:18 ` Deven Bowers
2020-08-10 23:05 ` Al Viro
2020-08-11 8:49 ` Mickaël Salaün
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