On 1/28/20 9:17 AM, Stefan Metzmacher wrote: > Am 28.01.20 um 17:10 schrieb Jens Axboe: >> On 1/28/20 3:18 AM, Stefan Metzmacher wrote: >>> Hi Jens, >>> >>> now that we have IORING_FEAT_CUR_PERSONALITY... >>> >>> How can we optimize the fileserver case now, in order to avoid the >>> overhead of always calling 5 syscalls before io_uring_enter()?: >>> >>> /* gain root again */ >>> setresuid(-1,0,-1); setresgid(-1,0,-1) >>> /* impersonate the user with groups */ >>> setgroups(num, grps); setresgid(-1,gid,-1); setresuid(-1,uid,-1); >>> /* trigger the operation */ >>> io_uring_enter(); >>> >>> I guess some kind of IORING_REGISTER_CREDS[_UPDATE] would be >>> good, together with a IOSQE_FIXED_CREDS in order to specify >>> credentials per operation. >>> >>> Or we make it much more generic and introduce a credsfd_create() >>> syscall in order to get an fd for a credential handle, maybe >>> together with another syscall to activate the credentials of >>> the current thread (or let a write to the fd trigger the activation >>> in order to avoid an additional syscall number). >>> >>> Having just an fd would allow IORING_REGISTER_CREDS[_UPDATE] >>> to be just an array of int values instead of a more complex >>> structure to define the credentials. >> >> I'd rather avoid having to add more infrastructure for this, even if >> credsfd_create() would be nifty. >> >> With that in mind, something like: >> >> - Application does IORING_REGISTER_CREDS, which returns some index >> >> - Add a IORING_OP_USE_CREDS opcode, which sets the creds associated >> with dependent commands >> - Actual request is linked to the IORING_OP_USE_CREDS command, any >> link off IORING_OP_USE_CREDS will use those credentials > > Using links for this sounds ok. Great! I'll try and hack this up and see how it turns out. >> - IORING_UNREGISTER_CREDS removes the registered creds >> >> Just throwing that out there, definitely willing to entertain other >> methods that make sense for this. Trying to avoid needing to put this >> information in the SQE itself, hence the idea to use a chain of links >> for it. >> >> The downside is that we'll need to maintain an array of key -> creds, >> but that's probably not a big deal. >> >> What do you think? > > So IORING_REGISTER_CREDS would be a simple operation that just takes a > snapshot of the current_cred() and returns an id that can be passed to > IORING_OP_USE_CREDS or IORING_UNREGISTER_CREDS? Right, you would not pass in any arguments, it'd have to be run from the personality you wish to register. It simply returns an integer, which is a key to use for IORING_OP_USE_CREDS, or at the end for IORING_UNREGISTER_CREDS when you no longer wish to use this personality. >> Ideally I'd like to get this done for 5.6 even if we >> are a bit late, so you'll have everything you need with that release. > > That would be great! Crossing fingers... -- Jens Axboe
