[kernel] Fix dmesg_restrict patch to avoid regression (rhbz 952655)
Josh Boyer
jwboyer at fedoraproject.org
Tue May 7 16:35:26 UTC 2013
commit 9f4a5ddbaf0434e5c83f5f27dd79b00f28c14079
Author: Josh Boyer <jwboyer at redhat.com>
Date: Tue May 7 12:29:25 2013 -0400
Fix dmesg_restrict patch to avoid regression (rhbz 952655)
...g-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch | 182 +++++++++++++------
kernel.spec | 3 +
2 files changed, 127 insertions(+), 58 deletions(-)
---
diff --git a/0001-kmsg-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch b/0001-kmsg-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch
index c42c8c4..7197f7f 100644
--- a/0001-kmsg-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch
+++ b/0001-kmsg-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch
@@ -1,33 +1,106 @@
-From ce10d1b72b4da3c98bbbcb1b945687d964c31923 Mon Sep 17 00:00:00 2001
-From: Josh Boyer <jwboyer at redhat.com>
-Date: Tue, 9 Apr 2013 11:08:13 -0400
-Subject: [PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg
+To fix /dev/kmsg, let's compare the existing interfaces and what they allow:
-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.
+- /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.
-Fix this by reworking all of the access methods to use the
-check_syslog_permissions function and adding checks to devkmsg_open and
-devkmsg_read.
+- syslog syscall allows:
+ - anything, if CAP_SYSLOG.
+ - 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 at chromium.org>
Reported-by: Christian Kujau <lists at nerdbynature.de>
-CC: stable at vger.kernel.org
-Signed-off-by: Eric Paris <eparis at redhat.com>
-Signed-off-by: Josh Boyer <jwboyer at redhat.com>
+Cc: Josh Boyer <jwboyer at redhat.com>
+Cc: Kay Sievers <kay at vrfy.org>
+Cc: stable at vger.kernel.org
---
- kernel/printk.c | 91 +++++++++++++++++++++++++++++----------------------------
- 1 file changed, 47 insertions(+), 44 deletions(-)
+ fs/proc/kmsg.c | 10 +++---
+ 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
-index abbdd9e..5541095 100644
+index abbdd9e..53b5c5e 100644
--- a/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++;
}
@@ -41,8 +114,12 @@ index abbdd9e..5541095 100644
+{
+ if (dmesg_restrict)
+ 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)
@@ -52,55 +129,42 @@ index abbdd9e..5541095 100644
+ * already done the capabilities checks at open time.
+ */
+ if (from_file && type != SYSLOG_ACTION_OPEN)
-+ goto ok;
++ return 0;
+
+ if (syslog_action_restricted(type)) {
+ if (capable(CAP_SYSLOG))
-+ goto ok;
-+ /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
++ return 0;
++ /*
++ * For historical reasons, accept CAP_SYS_ADMIN too, with
++ * a warning.
++ */
+ if (capable(CAP_SYS_ADMIN)) {
+ printk_once(KERN_WARNING "%s (%d): "
+ "Attempt to access syslog with CAP_SYS_ADMIN "
+ "but no CAP_SYSLOG (deprecated).\n",
+ current->comm, task_pid_nr(current));
-+ goto ok;
++ return 0;
+ }
+ return -EPERM;
+ }
-+ok:
+ return security_syslog(type);
+}
+
++
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
u64 seq;
-@@ -443,10 +483,16 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
- 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)
+@@ -624,7 +671,8 @@ static int devkmsg_open(struct inode *inode, struct file *file)
if ((file->f_flags & O_ACCMODE) == O_WRONLY)
return 0;
- 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)
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
@@ -146,17 +210,19 @@ index abbdd9e..5541095 100644
#if defined(CONFIG_PRINTK_TIME)
static bool printk_time = 1;
#else
-@@ -1131,10 +1138,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
- if (error)
- goto out;
+@@ -1253,7 +1262,7 @@ out:
-- error = security_syslog(type);
-- if (error)
-- return error;
--
- switch (type) {
- case SYSLOG_ACTION_CLOSE: /* Close log */
- break;
+ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
+ {
+- return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
++ return do_syslog(type, buf, len, SYSLOG_FROM_READER);
+ }
+
+ /*
--
-1.8.1.4
+1.7.9.5
+
+--
+Kees Cook
+Chrome OS Security
diff --git a/kernel.spec b/kernel.spec
index b820a6a..a396c1c 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -2240,6 +2240,9 @@ fi
# ||----w |
# || ||
%changelog
+* Tue May 07 2013 Josh Boyer <jwboyer at redhat.com>
+- Fix dmesg_restrict patch to avoid regression (rhbz 952655)
+
* Mon May 06 2013 Josh Boyer <jwboyer at redhat.com> - 3.10.0-0.rc0.git19.1
- Linux v3.9-10936-g51a26ae
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