Well, I've gone through hell trying to fix the rename()/rmdir()/remove()
races and failed utterly. There are far more race conditions then even
my last posting indicated, and there are *severe* problems fixing NFS
to deal with even Ian's suggestion... it turns out that NFS's nfs_namei()
permanently adjusts the mbuf while processing the path name, making
restarts impossible.
The only solution is to implement namei cache path locking and formalize
the 'nameidata' structure, which means ripping up a lot of code because
nearly the entire code base currently plays with the contents of
'nameidata' willy-nilly. Nothing else will work. It's not something
that I can consider doing now.
In the mean time I am going to remove the panic()'s in question. This
means that in ufs_rename() the machine will silently ignore the race
(not do the rename) instead of panic. It's all that can be done for
the moment. It solve the security/attack issue. We'll have to attack
the races as a separate issue. The patch to remove the panics is utterly
trivial and I will commit it after I test it.
-Matt
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