On Wed, Feb 27, 2013 at 09:54:27AM -0800, Kees Cook wrote: > On Fri, Feb 22, 2013 at 01:18:57PM -0500, Josh Boyer wrote: > > 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 > > 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@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; > > + > > I think this should use check_syslog_permissions() instead, as done for > /proc/kmsg and the syslog syscall. > > err = check_syslog_permissions(SYSLOG_ACTION_OPTION, SYSLOG_FROM_FILE); Did you mean SYSLOG_ACTION_OPEN? I didn't code it that way because the comment in that function about the capability checks already being done seem pretty off to me. I could have just misread the /proc code though. I can resend with the change you suggest if everyone thinks that's a better way. Also, the LSM hooks aren't doing any capability checks at all that I can see, which may or may not be a bug in and of itself but I have no idea. I was hoping Eric would speak up about that. > if (err) > return err; > > And going forward we should probably think about dropping the CAP_SYS_ADMIN > backward-compat code in check_syslog_permissions. Sure, but that's a separate commit. josh -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html