Chris PeBenito <chpebeni@xxxxxxxxxxxxxxxxxxx> writes: > On 2/8/2022 09:17, William Roberts wrote: >> <snip> >> This is getting too long for me. >> >>>> >>>> I don't have a strong opinion either way. If one were to allow this >>>> using a policy rule, it would result in a major policy breakage. The >>>> rule would turn on extended perm checks across the entire system, >>>> which the SELinux Reference Policy isn't written for. I can't speak >>>> to the Android policy, but I would imagine it would be the similar >>>> problem there too. >>> >>> Excuse me if I am wrong but AFAIK adding a xperm rule does not turn on >>> xperm checks across the entire system. >> It doesn't as you state below its target + class. >> >>> >>> If i am not mistaken it will turn on xperm checks only for the >>> operations that have the same source and target/target class. >> That's correct. > > Just to clarify (Demi Marie also mentioned this earlier in the > thread), what I originally meant was how to emulate this patch by > using policy rules means you need a rule that allows the two ioctls on > all domains for all objects. That results in xperms checks enabled > everywhere. Thanks. That is clear now. I also learned that is pretty much what Android's sepolicy is doing. That is probably not something I would do (enable xperms globally). I would probably leverage it only for "devnode" chr and maybe blk files and only where they actually are accessed. I would not mind removing these two checks, but i am not a big user of xperms (i only filter TIOSCTI on terminal chr files and only for the entities that write or append them). > > >>> This is also why i don't (with the exception TIOSCTI for termdev >>> chr_file) use xperms by default. >>> >>> 1. it is really easy to selectively filter ioctls by adding xperm rules >>> for end users (and since ioctls are often device/driver specific they >>> know best what is needed and what not) >> >>>>>> and FIONCLEX can be trivially bypassed unless fcntl(F_SETFD) >>> >>> 2. if you filter ioctls in upstream policy for example like i do with >>> TIOSCTI using for example (allowx foo bar (ioctl chr_file (not >>> (0xXXXX)))) then you cannot easily exclude additional ioctls later where source is >>> foo and target/tclass is bar/chr_file because there is already a rule in >>> place allowing the ioctl (and you cannot add rules) >> Currently, fcntl flag F_SETFD is never checked, it's silently >> allowed, but >> the equivalent FIONCLEX and FIOCLEX are checked. So if you wrote policy >> to block the FIO*CLEX flags, it would be bypassable through F_SETFD and >> FD_CLOEXEC. So the patch proposed makes the FIO flags behave like >> F_SETFD. Which means upstream policy users could drop this allow, which >> could then remove the target/class rule and allow all icotls. Which is easy >> to prevent and fix you could be a rule in to allowx 0 as documented in the >> wiki: https://selinuxproject.org/page/XpermRules >> The questions I think we have here are: >> 1. Do we agree that the behavior between SETFD and the FIO flags are equivalent? >> I think they are. >> 2. Do we want the interfaces to behave the same? >> I think they should. > > If you can bypass FIONCLEX and FIOCLEX checks by F_SETFD and > FD_CLOEXEC, then I agree that the two FIO checks don't have value and > can be skipped as F_SETFD is. > >> 3. Do upstream users of the policy construct care? >> The patch is backwards compat, but I don't want their to be cruft >> floating around with extra allowxperm rules. > > Reference policy does not have any xperm rules at this time. I looked > at the Fedora policy, and that doesn't have any. -- gpg --locate-keys dominick.grift@xxxxxxxxxxx Key fingerprint = FCD2 3660 5D6B 9D27 7FC6 E0FF DA7E 521F 10F6 4098 Dominick Grift
