When a process successfully get an fd using
open(flags=O_RDWR), it will be able to read/write to that file as long as the fd isn't closed (Regular file on local filesystem), even if some other process use chmod to cancel the read/write permission for the corresponding user. Does Linux kernel check file permissions on inode or open file description? But how about when the process try to execute that file using
execveat, will the kernel read the disk to check the x bit and suid bit permission? What kind of permissions are recorded in open file description, does it contain a full ACL or simply readable/writable bit so every operation else(
fchmod, etc) will check the on-disk info?
What if I transfer this fd to another process of another whose fsuid doesn't have read/write/execute bit on that file(according to the on-disk filesystem info), will that receiver process be able to read/write/execute the file through the fd?