6pack: fix free memory scribbles
commit acf673a318
fixed a user triggerable free
memory scribble but in doing so replaced it with a different one that allows
the user to control the data and scribble even more.
sixpack_close is called by the tty layer in tty context. The tty context is
protected by sp_get() and sp_put(). However network layer activity via
sp_xmit() is not protected this way. We must therefore stop the queue
otherwise the user gets to dump a buffer mostly of their choice into freed
kernel pages.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -683,6 +683,12 @@ static void sixpack_close(struct tty_struct *tty)
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if (!atomic_dec_and_test(&sp->refcnt))
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down(&sp->dead_sem);
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/* We must stop the queue to avoid potentially scribbling
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* on the free buffers. The sp->dead_sem is not sufficient
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* to protect us from sp->xbuff access.
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*/
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netif_stop_queue(sp->dev);
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del_timer_sync(&sp->tx_t);
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del_timer_sync(&sp->resync_t);
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