Re:PolicyKit: Users with UID greater than INT_MAX can execut...
by jabl on Wednesday December 05, 2018 @09:12AM
(#18608293)
Others pointed out that nobody was (uint16_t) -2, or 65534.
But, it turns out this value is, in fact, special in current day Linux as well. It's the default value of the special 'overflow' uid, can be seen/set at /proc/sys/fs/overflowuid.
Apart from some legacy stuff using 16-bit uid's, today it's mostly used for two things
1) In NFS, if mapping a user fails, then it gets assigned the overflowuid.
2) In containers with user namespaces, unmapped users again get the overflowuid.
But, it turns out this value is, in fact, special in current day Linux as well. It's the default value of the special 'overflow' uid, can be seen/set at /proc/sys/fs/overflowuid.
Apart from some legacy stuff using 16-bit uid's, today it's mostly used for two things
1) In NFS, if mapping a user fails, then it gets assigned the overflowuid.
2) In containers with user namespaces, unmapped users again get the overflowuid.
For more details, see https://lwn.net/Articles/695478/