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637241a900
The dmesg_restrict sysctl currently covers the syslog method for access
dmesg, however /dev/kmsg isn't covered by the same protections. Most
people haven't noticed because util-linux dmesg(1) defaults to using the
syslog method for access in older versions. With util-linux dmesg(1)
defaults to reading directly from /dev/kmsg.
To fix /dev/kmsg, let's compare the existing interfaces and what they
allow:
- /proc/kmsg allows:
- open (SYSLOG_ACTION_OPEN) if CAP_SYSLOG since it uses a destructive
single-reader interface (SYSLOG_ACTION_READ).
- everything, after an open.
- syslog syscall allows:
- anything, if CAP_SYSLOG.
- SYSLOG_ACTION_READ_ALL and SYSLOG_ACTION_SIZE_BUFFER, if
dmesg_restrict==0.
- nothing else (EPERM).
The use-cases were:
- dmesg(1) needs to do non-destructive SYSLOG_ACTION_READ_ALLs.
- sysklog(1) needs to open /proc/kmsg, drop privs, and still issue the
destructive SYSLOG_ACTION_READs.
AIUI, dmesg(1) is moving to /dev/kmsg, and systemd-journald doesn't
clear the ring buffer.
Based on the comments in devkmsg_llseek, it sounds like actions besides
reading aren't going to be supported by /dev/kmsg (i.e.
SYSLOG_ACTION_CLEAR), so we have a strict subset of the non-destructive
syslog syscall actions.
To this end, move the check as Josh had done, but also rename the
constants to reflect their new uses (SYSLOG_FROM_CALL becomes
SYSLOG_FROM_READER, and SYSLOG_FROM_FILE becomes SYSLOG_FROM_PROC).
SYSLOG_FROM_READER allows non-destructive actions, and SYSLOG_FROM_PROC
allows destructive actions after a capabilities-constrained
SYSLOG_ACTION_OPEN check.
- /dev/kmsg allows:
- open if CAP_SYSLOG or dmesg_restrict==0
- reading/polling, after open
Addresses https://bugzilla.redhat.com/show_bug.cgi?id=903192
[akpm@linux-foundation.org: use pr_warn_once()]
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Christian Kujau <lists@nerdbynature.de>
Tested-by: Josh Boyer <jwboyer@redhat.com>
Cc: Kay Sievers <kay@vrfy.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
53 lines
1.9 KiB
C
53 lines
1.9 KiB
C
/* Syslog internals
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*
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* Copyright 2010 Canonical, Ltd.
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* Author: Kees Cook <kees.cook@canonical.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#ifndef _LINUX_SYSLOG_H
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#define _LINUX_SYSLOG_H
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/* Close the log. Currently a NOP. */
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#define SYSLOG_ACTION_CLOSE 0
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/* Open the log. Currently a NOP. */
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#define SYSLOG_ACTION_OPEN 1
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/* Read from the log. */
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#define SYSLOG_ACTION_READ 2
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/* Read all messages remaining in the ring buffer. */
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#define SYSLOG_ACTION_READ_ALL 3
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/* Read and clear all messages remaining in the ring buffer */
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#define SYSLOG_ACTION_READ_CLEAR 4
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/* Clear ring buffer. */
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#define SYSLOG_ACTION_CLEAR 5
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/* Disable printk's to console */
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#define SYSLOG_ACTION_CONSOLE_OFF 6
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/* Enable printk's to console */
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#define SYSLOG_ACTION_CONSOLE_ON 7
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/* Set level of messages printed to console */
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#define SYSLOG_ACTION_CONSOLE_LEVEL 8
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/* Return number of unread characters in the log buffer */
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#define SYSLOG_ACTION_SIZE_UNREAD 9
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/* Return size of the log buffer */
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#define SYSLOG_ACTION_SIZE_BUFFER 10
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#define SYSLOG_FROM_READER 0
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#define SYSLOG_FROM_PROC 1
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int do_syslog(int type, char __user *buf, int count, bool from_file);
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#endif /* _LINUX_SYSLOG_H */
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