From: "Frank Filz" <ffilzlnx@mindspring.com>
To: "'Andy Lutomirski'" <luto@kernel.org>, <security@kernel.org>
Cc: "'Konstantin Khlebnikov'" <koct9i@gmail.com>,
"'Alexander Viro'" <viro@zeniv.linux.org.uk>,
"'Kees Cook'" <keescook@chromium.org>,
"'Willy Tarreau'" <w@1wt.eu>, <linux-mm@kvack.org>,
"'Andrew Morton'" <akpm@linux-foundation.org>,
"'yalin wang'" <yalin.wang2010@gmail.com>,
"'Linux Kernel Mailing List'" <linux-kernel@vger.kernel.org>,
"'Jan Kara'" <jack@suse.cz>,
"'Linux FS Devel'" <linux-fsdevel@vger.kernel.org>
Subject: RE: [PATCH 2/2] fs: Harden against open(..., O_CREAT, 02777) in a setgid directory
Date: Wed, 25 Jan 2017 15:17:16 -0800 [thread overview]
Message-ID: <014401d27761$2c79f990$856decb0$@mindspring.com> (raw)
In-Reply-To: <826ec4aab64ec304944098d15209f8c1ae65bb29.1485377903.git.luto@kernel.org>
> Currently, if you open("foo", O_WRONLY | O_CREAT | ..., 02777) in a
> directory that is setgid and owned by a different gid than current's
fsgid, you
> end up with an SGID executable that is owned by the directory's GID. This
is
> a Bad Thing (tm). Exploiting this is nontrivial because most ways of
creating a
> new file create an empty file and empty executables aren't particularly
> interesting, but this is nevertheless quite dangerous.
>
> Harden against this type of attack by detecting this particular corner
case
> (unprivileged program creates SGID executable inode in SGID directory
> owned by a different GID) and clearing the new inode's SGID bit.
Nasty.
I'd love to see a test for this in xfstests and/or pjdfstests...
Frank
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WARNING: multiple messages have this Message-ID (diff)
From: "Frank Filz" <ffilzlnx@mindspring.com>
To: 'Andy Lutomirski' <luto@kernel.org>, security@kernel.org
Cc: 'Konstantin Khlebnikov' <koct9i@gmail.com>,
'Alexander Viro' <viro@zeniv.linux.org.uk>,
'Kees Cook' <keescook@chromium.org>, 'Willy Tarreau' <w@1wt.eu>,
linux-mm@kvack.org, 'Andrew Morton' <akpm@linux-foundation.org>,
'yalin wang' <yalin.wang2010@gmail.com>,
'Linux Kernel Mailing List' <linux-kernel@vger.kernel.org>,
'Jan Kara' <jack@suse.cz>,
'Linux FS Devel' <linux-fsdevel@vger.kernel.org>
Subject: RE: [PATCH 2/2] fs: Harden against open(..., O_CREAT, 02777) in a setgid directory
Date: Wed, 25 Jan 2017 15:17:16 -0800 [thread overview]
Message-ID: <014401d27761$2c79f990$856decb0$@mindspring.com> (raw)
In-Reply-To: <826ec4aab64ec304944098d15209f8c1ae65bb29.1485377903.git.luto@kernel.org>
> Currently, if you open("foo", O_WRONLY | O_CREAT | ..., 02777) in a
> directory that is setgid and owned by a different gid than current's
fsgid, you
> end up with an SGID executable that is owned by the directory's GID. This
is
> a Bad Thing (tm). Exploiting this is nontrivial because most ways of
creating a
> new file create an empty file and empty executables aren't particularly
> interesting, but this is nevertheless quite dangerous.
>
> Harden against this type of attack by detecting this particular corner
case
> (unprivileged program creates SGID executable inode in SGID directory
> owned by a different GID) and clearing the new inode's SGID bit.
Nasty.
I'd love to see a test for this in xfstests and/or pjdfstests...
Frank
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To unsubscribe, send a message with 'unsubscribe linux-mm' in
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WARNING: multiple messages have this Message-ID (diff)
From: "Frank Filz" <ffilzlnx@mindspring.com>
To: "'Andy Lutomirski'" <luto@kernel.org>, <security@kernel.org>
Cc: "'Konstantin Khlebnikov'" <koct9i@gmail.com>,
"'Alexander Viro'" <viro@zeniv.linux.org.uk>,
"'Kees Cook'" <keescook@chromium.org>,
"'Willy Tarreau'" <w@1wt.eu>, <linux-mm@kvack.org>,
"'Andrew Morton'" <akpm@linux-foundation.org>,
"'yalin wang'" <yalin.wang2010@gmail.com>,
"'Linux Kernel Mailing List'" <linux-kernel@vger.kernel.org>,
"'Jan Kara'" <jack@suse.cz>,
"'Linux FS Devel'" <linux-fsdevel@vger.kernel.org>
Subject: RE: [PATCH 2/2] fs: Harden against open(..., O_CREAT, 02777) in a setgid directory
Date: Wed, 25 Jan 2017 15:17:16 -0800 [thread overview]
Message-ID: <014401d27761$2c79f990$856decb0$@mindspring.com> (raw)
In-Reply-To: <826ec4aab64ec304944098d15209f8c1ae65bb29.1485377903.git.luto@kernel.org>
> Currently, if you open("foo", O_WRONLY | O_CREAT | ..., 02777) in a
> directory that is setgid and owned by a different gid than current's
fsgid, you
> end up with an SGID executable that is owned by the directory's GID. This
is
> a Bad Thing (tm). Exploiting this is nontrivial because most ways of
creating a
> new file create an empty file and empty executables aren't particularly
> interesting, but this is nevertheless quite dangerous.
>
> Harden against this type of attack by detecting this particular corner
case
> (unprivileged program creates SGID executable inode in SGID directory
> owned by a different GID) and clearing the new inode's SGID bit.
Nasty.
I'd love to see a test for this in xfstests and/or pjdfstests...
Frank
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
next prev parent reply other threads:[~2017-01-25 23:17 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-25 21:06 [PATCH 0/2] setgid hardening Andy Lutomirski
2017-01-25 21:06 ` Andy Lutomirski
2017-01-25 21:06 ` [PATCH 1/2] fs: Check f_cred instead of current's creds in should_remove_suid() Andy Lutomirski
2017-01-25 21:06 ` Andy Lutomirski
2017-01-25 21:43 ` Ben Hutchings
2017-01-25 21:48 ` Andy Lutomirski
2017-01-25 21:48 ` Andy Lutomirski
2017-01-25 23:15 ` Frank Filz
2017-01-25 23:15 ` Frank Filz
2017-01-25 23:15 ` Frank Filz
2017-01-26 0:12 ` Kees Cook
2017-01-26 0:12 ` Kees Cook
2017-01-25 21:06 ` [PATCH 2/2] fs: Harden against open(..., O_CREAT, 02777) in a setgid directory Andy Lutomirski
2017-01-25 21:06 ` Andy Lutomirski
2017-01-25 21:31 ` Ben Hutchings
2017-01-25 21:44 ` Andy Lutomirski
2017-01-25 21:44 ` Andy Lutomirski
2017-01-25 23:17 ` Frank Filz [this message]
2017-01-25 23:17 ` Frank Filz
2017-01-25 23:17 ` Frank Filz
2017-01-25 23:50 ` Willy Tarreau
2017-01-25 23:50 ` Willy Tarreau
2017-01-25 23:59 ` [PATCH 0/2] setgid hardening Willy Tarreau
2017-01-25 23:59 ` Willy Tarreau
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