[PATCH] kmsg: Honor dmesg_restrict sysctl on /dev/kmsg

From: Josh Boyer
Date: Fri Feb 22 2013 - 13:19:09 EST

Originally, the addition of 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

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@xxxxxxxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxx>
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;

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