cap_syslog: don't use WARN_ONCE for CAP_SYS_ADMIN deprecation warning

syslog-ng versions before 3.3.0beta1 (2011-05-12) assume that
CAP_SYS_ADMIN is sufficient to access syslog, so ever since CAP_SYSLOG
was introduced (2010-11-25) they have triggered a warning.

Commit ee24aebffb75 ("cap_syslog: accept CAP_SYS_ADMIN for now")
improved matters a little by making syslog-ng work again, just keeping
the WARN_ONCE().  But still, this is a warning that writes a stack trace
we don't care about to syslog, sets a taint flag, and alarms sysadmins
when nothing worse has happened than use of an old userspace with a
recent kernel.

Convert the WARN_ONCE to a printk_once to avoid that while continuing to
give userspace developers a hint that this is an unwanted
backward-compatibility feature and won't be around forever.

Reported-by: Ralf Hildebrandt <ralf.hildebrandt@charite.de>
Reported-by: Niels <zorglub_olsen@hotmail.com>
Reported-by: Paweł Sikora <pluto@agmk.net>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Liked-by: Gergely Nagy <algernon@madhouse-project.org>
Acked-by: Serge Hallyn <serge@hallyn.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 37dff3429adb..836a2ae0ac31 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -318,8 +318,10 @@ static int check_syslog_permissions(int type, bool from_file)
                         return 0;
                 /* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
                 if (capable(CAP_SYS_ADMIN)) {
-                        WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
-                                 "but no CAP_SYSLOG (deprecated).\n");
+                        printk_once(KERN_WARNING "%s (%d): "
+                                 "Attempt to access syslog with CAP_SYS_ADMIN "
+                                 "but no CAP_SYSLOG (deprecated).\n",
+                                 current->comm, task_pid_nr(current));
                         return 0;
                 }
                 return -EPERM;