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Fix dmesg_restrict patch to avoid regression (rhbz 952655)

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Josh Boyer 2013-05-07 12:29:25 -04:00
parent 717c453625
commit 9f4a5ddbaf
2 changed files with 127 additions and 58 deletions
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182
0001-kmsg-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch
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@ -1,33 +1,106 @@
From ce10d1b72b4da3c98bbbcb1b945687d964c31923 Mon Sep 17 00:00:00 2001 To fix /dev/kmsg, let's compare the existing interfaces and what they allow:
From: Josh Boyer <jwboyer@redhat.com>
Date: Tue, 9 Apr 2013 11:08:13 -0400
Subject: [PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg
The dmesg_restrict sysctl currently covers the syslog method for access - /proc/kmsg allows:
dmesg, however /dev/kmsg isn't covered by the same protections. Most  - open (SYSLOG_ACTION_OPEN) if CAP_SYSLOG since it uses a destructive
people haven't noticed because util-linux dmesg(1) defaults to using the single-reader interface (SYSLOG_ACTION_READ).
syslog method for access in older versions. With util-linux dmesg(1)  - everything, after an open.
defaults to reading directly from /dev/kmsg.
Fix this by reworking all of the access methods to use the - syslog syscall allows:
check_syslog_permissions function and adding checks to devkmsg_open and  - anything, if CAP_SYSLOG.
devkmsg_read.  - SYSLOG_ACTION_READ_ALL and SYSLOG_ACTION_SIZE_BUFFER, if dmesg_restrict==0.
 - nothing else (EPERM).
This fixes https://bugzilla.redhat.com/show_bug.cgi?id=903192 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
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Christian Kujau <lists@nerdbynature.de> Reported-by: Christian Kujau <lists@nerdbynature.de>
CC: stable@vger.kernel.org Cc: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com> Cc: Kay Sievers <kay@vrfy.org>
Signed-off-by: Josh Boyer <jwboyer@redhat.com> Cc: stable@vger.kernel.org
--- ---
kernel/printk.c | 91 +++++++++++++++++++++++++++++---------------------------- fs/proc/kmsg.c | 10 +++---
1 file changed, 47 insertions(+), 44 deletions(-) include/linux/syslog.h | 4 +--
kernel/printk.c | 91 ++++++++++++++++++++++++++----------------------
3 files changed, 57 insertions(+), 48 deletions(-)
diff --git a/fs/proc/kmsg.c b/fs/proc/kmsg.c
index bd4b5a7..bdfabda 100644
--- a/fs/proc/kmsg.c
+++ b/fs/proc/kmsg.c
@@ -21,12 +21,12 @@ extern wait_queue_head_t log_wait;
static int kmsg_open(struct inode * inode, struct file * file)
{
- return do_syslog(SYSLOG_ACTION_OPEN, NULL, 0, SYSLOG_FROM_FILE);
+ return do_syslog(SYSLOG_ACTION_OPEN, NULL, 0, SYSLOG_FROM_PROC);
}
static int kmsg_release(struct inode * inode, struct file * file)
{
- (void) do_syslog(SYSLOG_ACTION_CLOSE, NULL, 0, SYSLOG_FROM_FILE);
+ (void) do_syslog(SYSLOG_ACTION_CLOSE, NULL, 0, SYSLOG_FROM_PROC);
return 0;
}
@@ -34,15 +34,15 @@ static ssize_t kmsg_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
if ((file->f_flags & O_NONBLOCK) &&
- !do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_FILE))
+ !do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_PROC))
return -EAGAIN;
- return do_syslog(SYSLOG_ACTION_READ, buf, count, SYSLOG_FROM_FILE);
+ return do_syslog(SYSLOG_ACTION_READ, buf, count, SYSLOG_FROM_PROC);
}
static unsigned int kmsg_poll(struct file *file, poll_table *wait)
{
poll_wait(file, &log_wait, wait);
- if (do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_FILE))
+ if (do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_PROC))
return POLLIN | POLLRDNORM;
return 0;
}
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index 3891139..98a3153 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -44,8 +44,8 @@
/* Return size of the log buffer */
#define SYSLOG_ACTION_SIZE_BUFFER 10
-#define SYSLOG_FROM_CALL 0
-#define SYSLOG_FROM_FILE 1
+#define SYSLOG_FROM_READER 0
+#define SYSLOG_FROM_PROC 1
int do_syslog(int type, char __user *buf, int count, bool from_file);
diff --git a/kernel/printk.c b/kernel/printk.c diff --git a/kernel/printk.c b/kernel/printk.c
index abbdd9e..5541095 100644 index abbdd9e..53b5c5e 100644
--- a/kernel/printk.c --- a/kernel/printk.c
+++ b/kernel/printk.c +++ b/kernel/printk.c
@@ -368,6 +368,46 @@ static void log_store(int facility, int level, @@ -368,6 +368,53 @@ static void log_store(int facility, int level,
log_next_seq++; log_next_seq++;
} }
@ -41,8 +114,12 @@ index abbdd9e..5541095 100644
+{ +{
+ if (dmesg_restrict) + if (dmesg_restrict)
+ return 1; + return 1;
+ /* Unless restricted, we allow "read all" and "get buffer size" for everybody */ + /*
+ return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER; + * Unless restricted, we allow "read all" and "get buffer size"
+ * for everybody.
+ */
+ return type != SYSLOG_ACTION_READ_ALL &&
+ type != SYSLOG_ACTION_SIZE_BUFFER;
+} +}
+ +
+static int check_syslog_permissions(int type, bool from_file) +static int check_syslog_permissions(int type, bool from_file)
@ -52,55 +129,42 @@ index abbdd9e..5541095 100644
+ * already done the capabilities checks at open time. + * already done the capabilities checks at open time.
+ */ + */
+ if (from_file && type != SYSLOG_ACTION_OPEN) + if (from_file && type != SYSLOG_ACTION_OPEN)
+ goto ok; + return 0;
+ +
+ if (syslog_action_restricted(type)) { + if (syslog_action_restricted(type)) {
+ if (capable(CAP_SYSLOG)) + if (capable(CAP_SYSLOG))
+ goto ok; + return 0;
+ /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */ + /*
+ * For historical reasons, accept CAP_SYS_ADMIN too, with
+ * a warning.
+ */
+ if (capable(CAP_SYS_ADMIN)) { + if (capable(CAP_SYS_ADMIN)) {
+ printk_once(KERN_WARNING "%s (%d): " + printk_once(KERN_WARNING "%s (%d): "
+ "Attempt to access syslog with CAP_SYS_ADMIN " + "Attempt to access syslog with CAP_SYS_ADMIN "
+ "but no CAP_SYSLOG (deprecated).\n", + "but no CAP_SYSLOG (deprecated).\n",
+ current->comm, task_pid_nr(current)); + current->comm, task_pid_nr(current));
+ goto ok; + return 0;
+ } + }
+ return -EPERM; + return -EPERM;
+ } + }
+ok:
+ return security_syslog(type); + return security_syslog(type);
+} +}
+
+ +
/* /dev/kmsg - userspace message inject/listen interface */ /* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user { struct devkmsg_user {
u64 seq; u64 seq;
@@ -443,10 +483,16 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, @@ -624,7 +671,8 @@ static int devkmsg_open(struct inode *inode, struct file *file)
char cont = '-';
size_t len;
ssize_t ret;
+ int err;
if (!user)
return -EBADF;
+ err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+ SYSLOG_FROM_FILE);
+ if (err)
+ return err;
+
ret = mutex_lock_interruptible(&user->lock);
if (ret)
return ret;
@@ -624,7 +670,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
if ((file->f_flags & O_ACCMODE) == O_WRONLY) if ((file->f_flags & O_ACCMODE) == O_WRONLY)
return 0; return 0;
- err = security_syslog(SYSLOG_ACTION_READ_ALL); - err = security_syslog(SYSLOG_ACTION_READ_ALL);
+ err = check_syslog_permissions(SYSLOG_ACTION_OPEN, SYSLOG_FROM_FILE); + err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
+ SYSLOG_FROM_READER);
if (err) if (err)
return err; return err;
@@ -817,45 +863,6 @@ static inline void boot_delay_msec(int level) @@ -817,45 +865,6 @@ static inline void boot_delay_msec(int level)
} }
#endif #endif
@ -146,17 +210,19 @@ index abbdd9e..5541095 100644
#if defined(CONFIG_PRINTK_TIME) #if defined(CONFIG_PRINTK_TIME)
static bool printk_time = 1; static bool printk_time = 1;
#else #else
@@ -1131,10 +1138,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file) @@ -1253,7 +1262,7 @@ out:
if (error)
goto out;
- error = security_syslog(type); SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
- if (error) {
- return error; - return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
- + return do_syslog(type, buf, len, SYSLOG_FROM_READER);
switch (type) { }
case SYSLOG_ACTION_CLOSE: /* Close log */
break; /*
-- --
1.8.1.4 1.7.9.5
--
Kees Cook
Chrome OS Security

3
kernel.spec
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@ -2240,6 +2240,9 @@ fi
# ||----w | # ||----w |
# || || # || ||
%changelog %changelog
* Tue May 07 2013 Josh Boyer <jwboyer@redhat.com>
- Fix dmesg_restrict patch to avoid regression (rhbz 952655)
* Mon May 06 2013 Josh Boyer <jwboyer@redhat.com> - 3.10.0-0.rc0.git19.1 * Mon May 06 2013 Josh Boyer <jwboyer@redhat.com> - 3.10.0-0.rc0.git19.1
- Linux v3.9-10936-g51a26ae - Linux v3.9-10936-g51a26ae