On Tue, Apr 30, 2013 at 11:35 AM, Josh Boyer <[email protected]> wrote: > On Tue, Apr 30, 2013 at 10:25:41AM -0700, Kees Cook wrote: >> 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 >> >> Signed-off-by: Kees Cook <[email protected]> >> Reported-by: Christian Kujau <[email protected]> >> Cc: Josh Boyer <[email protected]> >> Cc: Kay Sievers <[email protected]> >> Cc: [email protected] > > So staring at this for a while, I think it looks correct. It's > basically the same thing as the v3 I sent out, with the constant rename > and no check in devkmsg_read, right?
Yeah, I just explicitly clarified the use-cases and reasoning. :) > I'll try and get it tested here locally tomorrow. Great; thanks! -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
