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authorKees Cook <keescook@chromium.org>2013-06-12 14:04:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-06-12 16:29:44 -0700
commit637241a900cbd982f744d44646b48a273d609b34 (patch)
tree0c8e84af9e6a37bd61f9fc9b7a668472df53df46 /include/linux/syslog.h
parentcf7df378aa4ff7da3a44769b7ff6e9eef1a9f3db (diff)
downloadvexpress-lsk-637241a900cbd982f744d44646b48a273d609b34.tar.gz
kmsg: honor dmesg_restrict sysctl on /dev/kmsg
The dmesg_restrict sysctl currently covers the syslog method for access dmesg, however /dev/kmsg isn't covered by the same protections. Most people haven't noticed because util-linux dmesg(1) defaults to using the syslog method for access in older versions. With util-linux dmesg(1) defaults to reading directly from /dev/kmsg. To fix /dev/kmsg, let's compare the existing interfaces and what they allow: - /proc/kmsg allows: - open (SYSLOG_ACTION_OPEN) if CAP_SYSLOG since it uses a destructive single-reader interface (SYSLOG_ACTION_READ). - everything, after an open. - syslog syscall allows: - anything, if CAP_SYSLOG. - SYSLOG_ACTION_READ_ALL and SYSLOG_ACTION_SIZE_BUFFER, if dmesg_restrict==0. - nothing else (EPERM). The use-cases were: - dmesg(1) needs to do non-destructive SYSLOG_ACTION_READ_ALLs. - sysklog(1) needs to open /proc/kmsg, drop privs, and still issue the destructive SYSLOG_ACTION_READs. AIUI, dmesg(1) is moving to /dev/kmsg, and systemd-journald doesn't clear the ring buffer. Based on the comments in devkmsg_llseek, it sounds like actions besides reading aren't going to be supported by /dev/kmsg (i.e. SYSLOG_ACTION_CLEAR), so we have a strict subset of the non-destructive syslog syscall actions. To this end, move the check as Josh had done, but also rename the constants to reflect their new uses (SYSLOG_FROM_CALL becomes SYSLOG_FROM_READER, and SYSLOG_FROM_FILE becomes SYSLOG_FROM_PROC). SYSLOG_FROM_READER allows non-destructive actions, and SYSLOG_FROM_PROC allows destructive actions after a capabilities-constrained SYSLOG_ACTION_OPEN check. - /dev/kmsg allows: - open if CAP_SYSLOG or dmesg_restrict==0 - reading/polling, after open Addresses https://bugzilla.redhat.com/show_bug.cgi?id=903192 [akpm@linux-foundation.org: use pr_warn_once()] Signed-off-by: Kees Cook <keescook@chromium.org> Reported-by: Christian Kujau <lists@nerdbynature.de> Tested-by: Josh Boyer <jwboyer@redhat.com> Cc: Kay Sievers <kay@vrfy.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/syslog.h')
-rw-r--r--include/linux/syslog.h4
1 files changed, 2 insertions, 2 deletions
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index 38911391a13..98a3153c0f9 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -44,8 +44,8 @@
/* Return size of the log buffer */
#define SYSLOG_ACTION_SIZE_BUFFER 10
-#define SYSLOG_FROM_CALL 0
-#define SYSLOG_FROM_FILE 1
+#define SYSLOG_FROM_READER 0
+#define SYSLOG_FROM_PROC 1
int do_syslog(int type, char __user *buf, int count, bool from_file);