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

From: Andrew Morton
Date: Fri Mar 22 2013 - 17:55:02 EST

poke. Nothing got applied. I'll drop
kmsg-honor-dmesg_restrict-sysctl-on-dev-kmsg.patch, see if that has any
effect ;)

From: Josh Boyer <jwboyer@xxxxxxxxxx>
Subject: kmsg: honor dmesg_restrict sysctl on /dev/kmsg

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

Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxx>
Reported-by: Christian Kujau <lists@xxxxxxxxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

kernel/printk.c | 3 +++
1 file changed, 3 insertions(+)

diff -puN kernel/printk.c~kmsg-honor-dmesg_restrict-sysctl-on-dev-kmsg kernel/printk.c
--- a/kernel/printk.c~kmsg-honor-dmesg_restrict-sysctl-on-dev-kmsg
+++ a/kernel/printk.c
@@ -620,6 +620,9 @@ static int devkmsg_open(struct inode *in
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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