Hi Michal, On 21 December 2017 at 09:02, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > On Wed 20-12-17 17:17:46, Michael Kerrisk wrote: >> Hello Michal, >> >> On 20 December 2017 at 10:20, Michal Hocko <mhocko@xxxxxxxxxx> wrote: >> > On Tue 19-12-17 17:45:40, Michael Kerrisk wrote: >> >> But, is >> >> there a pressing reason to make the change? (Okay, I guess iterating >> >> using *_STAT is nicer than parsing /proc/sysvipc/*.) >> > >> > The reporter of this issue claims that "Reading /proc/sysvipc/shm is way >> > slower than executing the system call." I haven't checked that but I can >> > imagine that /proc/sysvipc/shm can take quite some time when there are >> > _many_ segments registered. >> >> Yes, that makes sense. >> >> > So they would like to use the syscall but >> > the interacting parties do not have compatible permissions. >> >> So, I don't think there is any security issue, since the same info is >> available in /proc/sysvipc/*. > > Well, I am not sure this is a valid argument (maybe I just misread your > statement). (Or perhaps I was not clear enough; see below) > Our security model _might_ be broken because of the sysipc > proc interface existance already. I am not saying it is broken because > I cannot see an attack vector based solely on the metadata information > knowledge. An attacker still cannot see/modify the real data. But maybe > there are some bugs lurking there and knowing the metadata might help to > exploit them. I dunno. > > You are certainly right that modifying/adding STAT flag to comply with > the proc interface permission model will not make the system any more > vulnerable, though. Yep, that was my point. Modifying _STAT behavior won't decrease security. That said, /proc/sysvipc/* has been around for a long time now, and nothing bad seems to have happened so far, AFAIK. >> The only question would be whether >> change in the *_STAT behavior might surprise some applications into >> behaving differently. I presume the chances of that are low, but if it >> was a concert, one could add new shmctl/msgctl/semctl *_STAT_ALL (or >> some such) operations that have the desired behavior. > > I would lean towards _STAT_ALL because this is Linux specific behavior > (I have looked at what BSD does here and they are checking permissions > for STAT as well). It would also be simpler to revert if we ever find > that this is a leak with security consequences. Oh -- I was unaware of this BSD behavior. At least on the various UNIX systems that I ever used SYSVIPC (including one or two ancient commercial BSD derivatives), ipcs(1) showed all IPC objects. (On FeeBSD, at least, it looks like ipcs(1) doesn't use the *_STAT interfaces.) Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
