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xen/netback: shutdown the ring if it contains garbage.
[ Upstream commit 48856286b64e4b66ec62b94e504d0b29c1ade664 ] A buggy or malicious frontend should not be able to confuse netback. If we spot anything which is not as it should be then shutdown the device and don't try to continue with the ring in a potentially hostile state. Well behaved and non-hostile frontends will not be penalised. As well as making the existing checks for such errors fatal also add a new check that ensures that there isn't an insane number of requests on the ring (i.e. more than would fit in the ring). If the ring contains garbage then previously is was possible to loop over this insane number, getting an error each time and therefore not generating any more pending requests and therefore not exiting the loop in xen_netbk_tx_build_gops for an externded period. Also turn various netdev_dbg calls which no precipitate a fatal error into netdev_err, they are rate limited because the device is shutdown afterwards. This fixes at least one known DoS/softlockup of the backend domain. Signed-off-by: Ian Campbell <firstname.lastname@example.org> Reviewed-by: Konrad Rzeszutek Wilk <email@example.com> Acked-by: Jan Beulich <JBeulich@suse.com> Signed-off-by: David S. Miller <firstname.lastname@example.org> Signed-off-by: Greg Kroah-Hartman <email@example.com>
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