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Documentation: Update netlink_mmap.txt
Update netlink_mmap.txt wrt. commit 4682a03586
("netlink: Always copy on mmap TX.").
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -199,16 +199,9 @@ frame header.
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TX limitations
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TX limitations
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Kernel processing usually involves validation of the message received by
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As of Jan 2015 the message is always copied from the ring frame to an
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user-space, then processing its contents. The kernel must assure that
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allocated buffer due to unresolved security concerns.
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userspace is not able to modify the message contents after they have been
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See commit 4682a0358639b29cf ("netlink: Always copy on mmap TX.").
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validated. In order to do so, the message is copied from the ring frame
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to an allocated buffer if either of these conditions is false:
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- only a single mapping of the ring exists
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- the file descriptor is not shared between processes
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This means that for threaded programs, the kernel will fall back to copying.
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Example
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Example
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