Messages in this thread |  | | Date | Fri, 13 Oct 2000 13:39:19 -0400 (EDT) | From | Alexander Viro <> | Subject | Re: [patch] For 2.4: syscall revoke. |
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On Fri, 13 Oct 2000, Dr. Werner Fink wrote:
> > Hi, > > hopefully this mail isn't lost because of a nervous `d' finger ;^) > Last week I've finished the work on the system call revoke for 2.4 and > done some changes on it suggested by the vendors security list. > > Due to the security issue of the syscall revoke, it would nice to see > this patch going in 2.4. This would help to close some open security > issues (e.g. user usage of vcs/vcsa and other devices). > > This implementation of sys_revoke not only removes all references > of a block or character special file but also all mmap vma's.
It's racey.
1) one process does read() on device, another does revoke() followed by rmmod. Oops - nothing holds module in memory, the first process is executing code from that module (->read(), that is) and we unmap that code.
2) every access to ->f_op suddenly becomes unsafe. Basically the same scenario, but here we have the window between fetching ->f_op and calling ->f_op->foo. You have no exclusion here, and even if you had, you still got #1 to deal with.
IOW, it's broken by design - you can't just drop ->f_op and call it quits. You certainly can't leave any process in the middle of code that becomes unprotected. And it's not an SMP-only problem - since ->read() may sleep you have #1 on UP too.
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