Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Mon, 23 Jan 2012 13:21:15 -0800 > Kees Cook <keescook@xxxxxxxxxxxx> wrote: > >> >> Add the "proc_pid_mem" sysctl to control whether or not /proc/pid/mem is >> allowed to work: 0: disabled, 1: read only, 2: read/write (default). >> >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >> --- >> v3: >> - document the default, thanks to Randy Dunlap. >> - remove needless CONFIG_PROC_FS checks, thanks to Eric W. Biederman. > > I was wondering about that. Is CONFIG_PROC_FS=n, CONFIG_SYSCTL=y an > impossible combination? If so, why? Fundamentally because the only way sysctls get to usespace is threw /proc/sys/. The binary sysctl emulation layer reads /proc/sys through the internal kernel mount. As I recall the symbol define tree: CONFIG_PROC_SYSCTL select CONFIG_SYSCTL CONFIG_PROC_SYSCTL depends on CONFIG_PROC_FS. And the only way CONFIG_SYSCTL gets set is if it is select. If anyone cares enough we can probably cleanup the Kconfig bits to have fewer symbols. At a practical level I think the real reason I objected is that it is ugly to just dump things into kernel/sysctl.c with #defines everywhere. Eric >> --- a/Documentation/sysctl/kernel.txt >> +++ b/Documentation/sysctl/kernel.txt >> @@ -56,6 +56,7 @@ show up in /proc/sys/kernel: >> - printk_delay >> - printk_ratelimit >> - printk_ratelimit_burst >> +- proc_pid_mem >> - randomize_va_space >> - real-root-dev ==> Documentation/initrd.txt >> - reboot-cmd [ SPARC only ] >> @@ -477,6 +478,20 @@ send before ratelimiting kicks in. >> >> ============================================================== >> >> +proc_pid_mem: >> + >> +This option can be used to select the level of access given to potential >> +ptracers when using the per-process "mem" file in /proc/pid/mem. >> + >> +0 - Disable entirely. >> + >> +1 - Allow potential ptracers read access to process memory, but not writes. >> + >> +2 - Allow potential ptracers read and write access to process memory. This >> + is the default. >> + >> +============================================================== > > I agree with Colin on this (he stole my line!). > > > > Overall, the patch looks really hacky and random. I felt the same way > as Vasily: it's easy to see how a significant number of similar (and > hacky and random) patches could be added, resulting in a regrettable > mess. > > Is there some better designed, more organized way of approaching all of > this? Random ideas: > > - A parallel /procfs-perms filesystem. You write a number into > /procfs-perms/stat to affect access to /proc/stat (although why the > heck not just run `chmod /proc/stat'?) It's unclear how to handle > /proc/pid/. Perhaps literally have a /procfs-perms/pid/ directory. > > - Make tasks inherit their /proc/pid/* permissions across fork, do a > chmod /proc/1/whatever in initscripts. > > - Other and better things ;) This particular approach makes my toes > curl. -- 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
