On Wed, May 8, 2013 at 2:22 PM, Andrew Morton <[email protected]> wrote: > On Tue, 30 Apr 2013 10:25:41 -0700 Kees Cook <[email protected]> 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 > > hm, that changelog is waaaay down in the weeds and anyone who hasn't > been following this with a microscope won't have a clue. > > I went into an earlier patch and dug out this: > > : 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. > : > : Addresses https://bugzilla.redhat.com/show_bug.cgi?id=903192 > > Which is still accurate and relevant, yes?
Yeah, that'll be fine. I kind of like having the longer rationale in the commit message for future reference (i.e. destructive vs non-destructive, etc), but I'd rather see the code fixed. :) -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/
