Fix dmesg_restrict patch to avoid regression (rhbz 952655)
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Josh Boyer
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717c453625
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9f4a5ddbaf
@ -1,33 +1,106 @@
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From ce10d1b72b4da3c98bbbcb1b945687d964c31923 Mon Sep 17 00:00:00 2001
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From: Josh Boyer <jwboyer@redhat.com>
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Date: Tue, 9 Apr 2013 11:08:13 -0400
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Subject: [PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg
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To fix /dev/kmsg, let's compare the existing interfaces and what they allow:
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The dmesg_restrict sysctl currently covers the syslog method for access
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dmesg, however /dev/kmsg isn't covered by the same protections. Most
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people haven't noticed because util-linux dmesg(1) defaults to using the
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syslog method for access in older versions. With util-linux dmesg(1)
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defaults to reading directly from /dev/kmsg.
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- /proc/kmsg allows:
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- open (SYSLOG_ACTION_OPEN) if CAP_SYSLOG since it uses a destructive
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single-reader interface (SYSLOG_ACTION_READ).
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- everything, after an open.
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Fix this by reworking all of the access methods to use the
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check_syslog_permissions function and adding checks to devkmsg_open and
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devkmsg_read.
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- syslog syscall allows:
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- anything, if CAP_SYSLOG.
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- SYSLOG_ACTION_READ_ALL and SYSLOG_ACTION_SIZE_BUFFER, if dmesg_restrict==0.
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- nothing else (EPERM).
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This fixes https://bugzilla.redhat.com/show_bug.cgi?id=903192
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The use-cases were:
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- dmesg(1) needs to do non-destructive SYSLOG_ACTION_READ_ALLs.
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- sysklog(1) needs to open /proc/kmsg, drop privs, and still issue the
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destructive SYSLOG_ACTION_READs.
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AIUI, dmesg(1) is moving to /dev/kmsg, and systemd-journald doesn't
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clear the ring buffer.
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Based on the comments in devkmsg_llseek, it sounds like actions besides
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reading aren't going to be supported by /dev/kmsg (i.e. SYSLOG_ACTION_CLEAR),
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so we have a strict subset of the non-destructive syslog syscall actions.
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To this end, move the check as Josh had done, but also rename the constants
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to reflect their new uses (SYSLOG_FROM_CALL becomes SYSLOG_FROM_READER, and
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SYSLOG_FROM_FILE becomes SYSLOG_FROM_PROC). SYSLOG_FROM_READER allows
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non-destructive actions, and SYSLOG_FROM_PROC allows destructive actions
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after a capabilities-constrained SYSLOG_ACTION_OPEN check.
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- /dev/kmsg allows:
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- open if CAP_SYSLOG or dmesg_restrict==0
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- reading/polling, after open
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Signed-off-by: Kees Cook <keescook@chromium.org>
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Reported-by: Christian Kujau <lists@nerdbynature.de>
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CC: stable@vger.kernel.org
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Signed-off-by: Eric Paris <eparis@redhat.com>
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Signed-off-by: Josh Boyer <jwboyer@redhat.com>
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Cc: Josh Boyer <jwboyer@redhat.com>
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Cc: Kay Sievers <kay@vrfy.org>
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Cc: stable@vger.kernel.org
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---
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kernel/printk.c | 91 +++++++++++++++++++++++++++++----------------------------
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1 file changed, 47 insertions(+), 44 deletions(-)
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fs/proc/kmsg.c | 10 +++---
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include/linux/syslog.h | 4 +--
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kernel/printk.c | 91 ++++++++++++++++++++++++++----------------------
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3 files changed, 57 insertions(+), 48 deletions(-)
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diff --git a/fs/proc/kmsg.c b/fs/proc/kmsg.c
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index bd4b5a7..bdfabda 100644
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--- a/fs/proc/kmsg.c
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+++ b/fs/proc/kmsg.c
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@@ -21,12 +21,12 @@ extern wait_queue_head_t log_wait;
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static int kmsg_open(struct inode * inode, struct file * file)
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{
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- return do_syslog(SYSLOG_ACTION_OPEN, NULL, 0, SYSLOG_FROM_FILE);
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+ return do_syslog(SYSLOG_ACTION_OPEN, NULL, 0, SYSLOG_FROM_PROC);
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}
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static int kmsg_release(struct inode * inode, struct file * file)
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{
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- (void) do_syslog(SYSLOG_ACTION_CLOSE, NULL, 0, SYSLOG_FROM_FILE);
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+ (void) do_syslog(SYSLOG_ACTION_CLOSE, NULL, 0, SYSLOG_FROM_PROC);
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return 0;
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}
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@@ -34,15 +34,15 @@ static ssize_t kmsg_read(struct file *file, char __user *buf,
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size_t count, loff_t *ppos)
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{
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if ((file->f_flags & O_NONBLOCK) &&
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- !do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_FILE))
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+ !do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_PROC))
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return -EAGAIN;
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- return do_syslog(SYSLOG_ACTION_READ, buf, count, SYSLOG_FROM_FILE);
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+ return do_syslog(SYSLOG_ACTION_READ, buf, count, SYSLOG_FROM_PROC);
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}
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static unsigned int kmsg_poll(struct file *file, poll_table *wait)
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{
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poll_wait(file, &log_wait, wait);
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- if (do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_FILE))
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+ if (do_syslog(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0, SYSLOG_FROM_PROC))
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return POLLIN | POLLRDNORM;
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return 0;
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}
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diff --git a/include/linux/syslog.h b/include/linux/syslog.h
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index 3891139..98a3153 100644
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--- a/include/linux/syslog.h
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+++ b/include/linux/syslog.h
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@@ -44,8 +44,8 @@
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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_CALL 0
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-#define SYSLOG_FROM_FILE 1
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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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diff --git a/kernel/printk.c b/kernel/printk.c
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index abbdd9e..5541095 100644
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index abbdd9e..53b5c5e 100644
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--- a/kernel/printk.c
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+++ b/kernel/printk.c
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@@ -368,6 +368,46 @@ static void log_store(int facility, int level,
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@@ -368,6 +368,53 @@ static void log_store(int facility, int level,
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log_next_seq++;
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}
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@ -41,8 +114,12 @@ index abbdd9e..5541095 100644
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+{
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+ if (dmesg_restrict)
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+ return 1;
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+ /* Unless restricted, we allow "read all" and "get buffer size" for everybody */
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+ return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
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+ /*
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+ * Unless restricted, we allow "read all" and "get buffer size"
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+ * for everybody.
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+ */
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+ return type != SYSLOG_ACTION_READ_ALL &&
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+ type != SYSLOG_ACTION_SIZE_BUFFER;
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+}
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+
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+static int check_syslog_permissions(int type, bool from_file)
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@ -52,55 +129,42 @@ index abbdd9e..5541095 100644
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+ * already done the capabilities checks at open time.
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+ */
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+ if (from_file && type != SYSLOG_ACTION_OPEN)
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+ goto ok;
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+ return 0;
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+
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+ if (syslog_action_restricted(type)) {
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+ if (capable(CAP_SYSLOG))
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+ goto ok;
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+ /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
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+ return 0;
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+ /*
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+ * For historical reasons, accept CAP_SYS_ADMIN too, with
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+ * a warning.
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+ */
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+ if (capable(CAP_SYS_ADMIN)) {
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+ printk_once(KERN_WARNING "%s (%d): "
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+ "Attempt to access syslog with CAP_SYS_ADMIN "
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+ "but no CAP_SYSLOG (deprecated).\n",
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+ current->comm, task_pid_nr(current));
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+ goto ok;
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+ return 0;
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+ }
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+ return -EPERM;
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+ }
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+ok:
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+ return security_syslog(type);
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+}
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+
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+
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/* /dev/kmsg - userspace message inject/listen interface */
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struct devkmsg_user {
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u64 seq;
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@@ -443,10 +483,16 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
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char cont = '-';
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size_t len;
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ssize_t ret;
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+ int err;
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if (!user)
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return -EBADF;
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+ err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
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+ SYSLOG_FROM_FILE);
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+ if (err)
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+ return err;
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+
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ret = mutex_lock_interruptible(&user->lock);
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if (ret)
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return ret;
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@@ -624,7 +670,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
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@@ -624,7 +671,8 @@ static int devkmsg_open(struct inode *inode, struct file *file)
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if ((file->f_flags & O_ACCMODE) == O_WRONLY)
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return 0;
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- err = security_syslog(SYSLOG_ACTION_READ_ALL);
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+ err = check_syslog_permissions(SYSLOG_ACTION_OPEN, SYSLOG_FROM_FILE);
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+ err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
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+ SYSLOG_FROM_READER);
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if (err)
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return err;
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@@ -817,45 +863,6 @@ static inline void boot_delay_msec(int level)
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@@ -817,45 +865,6 @@ static inline void boot_delay_msec(int level)
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}
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#endif
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@ -146,17 +210,19 @@ index abbdd9e..5541095 100644
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#if defined(CONFIG_PRINTK_TIME)
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static bool printk_time = 1;
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#else
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@@ -1131,10 +1138,6 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
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if (error)
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goto out;
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@@ -1253,7 +1262,7 @@ out:
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- error = security_syslog(type);
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- if (error)
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- return error;
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-
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switch (type) {
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case SYSLOG_ACTION_CLOSE: /* Close log */
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break;
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SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
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{
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- return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
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+ return do_syslog(type, buf, len, SYSLOG_FROM_READER);
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}
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/*
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--
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1.8.1.4
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1.7.9.5
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--
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Kees Cook
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Chrome OS Security
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@ -2240,6 +2240,9 @@ fi
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# ||----w |
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# || ||
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%changelog
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* Tue May 07 2013 Josh Boyer <jwboyer@redhat.com>
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- Fix dmesg_restrict patch to avoid regression (rhbz 952655)
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* Mon May 06 2013 Josh Boyer <jwboyer@redhat.com> - 3.10.0-0.rc0.git19.1
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- Linux v3.9-10936-g51a26ae
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