kernel/0001-kmsg-Honor-dmesg_restrict-sysctl-on-dev-kmsg.patch

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From feaf4959c30d0640093a607c577940d3e9351076 Mon Sep 17 00:00:00 2001
From: Josh Boyer <jwboyer@redhat.com>
Date: Fri, 22 Feb 2013 11:47:37 -0500
Subject: [PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg
Originally, the addition of the dmesg_restrict covered both the syslog
method of accessing dmesg, as well as /dev/kmsg itself. This was done
indirectly by security_syslog calling cap_syslog before doing any LSM
checks.
However, commit 12b3052c3ee (capabilities/syslog: open code cap_syslog
logic to fix build failure) moved the code around and pushed the checks
into the caller itself. That seems to have inadvertently dropped the
checks for dmesg_restrict on /dev/kmsg. Most people haven't noticed
because util-linux dmesg(1) defaults to using the syslog method for
access in older versions. With util-linux 2.22 and a kernel newer than
3.5, dmesg(1) defaults to reading directly from /dev/kmsg.
Fix this by making an explicit check in the devkmsg_open function.
This fixes https://bugzilla.redhat.com/show_bug.cgi?id=903192
Reported-by: Christian Kujau <lists@nerdbynature.de>
CC: stable@vger.kernel.org
Signed-off-by: Josh Boyer <jwboyer@redhat.com>
---
kernel/printk.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/printk.c b/kernel/printk.c
index f24633a..398ef9a 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -615,6 +615,9 @@ static int devkmsg_open(struct inode *inode, struct file *file)
struct devkmsg_user *user;
int err;
+ if (dmesg_restrict && !capable(CAP_SYSLOG))
+ return -EACCES;
+
/* write-only does not need any file context */
if ((file->f_flags & O_ACCMODE) == O_WRONLY)
return 0;
--
1.8.1.2