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SubjectRe: [PATCH] new syscall: flink
Once a process unlinks the last directory entry referencing a particular inode that it has an
open fd for and then passes the open fd to some other process (regardless of exactly how it does that), it seems to me that it has conceded any interest in the previous security constraints associated with that inode or with the recently
unlinked last directory entry for it. If the client process subsequently flink()s to the inode, it is merely a zerocopy file copy.

Since the client owns the new directory entry, it can chmod the inode to have any permissions it wants, create or modify an ACL where ACLs are in use, modify a capabilities mask more fine-grained than traditional unix permissions if something like that is in use, etc.

The cases with potential security implications are all in the context of flink()ing to an open fd for an inode that still corresponds to at least one directory entry.


Clayton Weaver

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