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. > - 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? > 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! Thanks! metze
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