On Tue, 15 Oct 2013 09:38:48 +1100 Ryan Mallon <rmallon@xxxxxxxxx> wrote: > Some setuid binaries will allow reading of files which have read > permission by the real user id. This is problematic with files which > use %pK because the file access permission is checked at open() time, > but the kptr_restrict setting is checked at read() time. If a setuid > binary opens a %pK file as an unprivileged user, and then elevates > permissions before reading the file, then kernel pointer values may be > leaked. > > This happens for example with the setuid pppd application on Ubuntu 12.04: > > $ head -1 /proc/kallsyms > 00000000 T startup_32 > > $ pppd file /proc/kallsyms > pppd: In file /proc/kallsyms: unrecognized option 'c1000000' > > This will only leak the pointer value from the first line, but other > setuid binaries may leak more information. > > Fix this by adding a check that in addition to the current process > having CAP_SYSLOG, that effective user and group ids are equal to the > real ids. If a setuid binary reads the contents of a file which uses > %pK then the pointer values will be printed as NULL if the real user > is unprivileged. > > Update the sysctl documentation to reflect the changes, and also > correct the documentation to state the kptr_restrict=0 is the default. > > This is a only temporary solution to the issue. The correct solution > is to do the permission check at open() time on files, and to replace > %pK with a function which checks the open() time permission. %pK uses > in printk should be removed since no sane permission check can be > done, and instead protected by using dmesg_restrict. I grabbed this and queued it for 3.13-rc1, marked for backporting into -stable. Given the amount of churn on this one I think it would be imprudent to put it into mainline immediately. I haven't been following the discussion very closely, so if anyone thinks it should be ungrabbed, please speak up. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
