On 5/13/17 4:54 AM, Jan Moskyto Matejka wrote: >> I see 2 problems: >> 1. the kernel is not telling the user the supplied buffer is too small >> (ie., if a single route does not fit in the skb then it should fail and >> return an error code to the user), > > Definitely. I want just to note that this condition usually occurs > somewhere during route dump. To know it before starting output, we would > have to walk the FIB once before dump to calculate max route len.
When adding a route to the skb, track whether it contains at least 1 route. If not, it means the next route in the dump is larger than the given buffer. Detect this condition and error out of the dump - returning an error to the user (-ENOSPC? or EMSGSIZE?) > >> 2. multipath routes for IPv4 and IPv6 do not have a limit. >> >> Should the kernel put a limit on the number of nexthops? I recently put >> a cap on MPLS route size as 4096 bytes, but I think this should be >> revisited in terms of a limit on number of nexthops to create a >> consistent limit even if struct sizes change. And, the limit on the >> number of nexthops should be consistent across address families (same >> limit for IPv4, IPv6, and MPLS). >> >> From discussions I have had, 32 nexthops for a single route is on the >> laughably high side, but some people do crazy things. How about a limit >> of 256 nexthops? > > 256 should be OK even for a crazy developer of BIRD. > > It would be nice to have if the returned error were somehow useful for > the userspace -- to know what is happening, not only something like > "impossible to add / append route". Top of tree kernel has extended error reporting so a message can be returned that says something to the effect of "route size is larger than supplied buffer size".
