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kern: tty: fix recanonicalization

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`ti->ti_begin` is actually the offset within the first block that is
unread, so we must use that for our lower bound.

Moving to the previous block has to be done at the end of the loop in
order to correctly handle the case of ti_begin == TTYINQ_DATASIZE.  At
that point, lastblock is still the last one with data written and the
next write into the queue would advance lastblock.  If we move to the
previous block at the beginning, then we're essentially off by one block
for the entire scan and run the risk of running off the end of the block
queue.

The ti_begin == 0 case is still handled correctly, as we skip the loop
entirely and the linestart gets recorded as the first byte available for
writing.  The bit after the loop about moving to the next block is also
still correct, even with both previous fixes in mind: we skipped moving
to the previous block if we hit ti_begin, and `off + 1` would in-fact be
a member of the next block from where we're reading if it falls on a
block boundary.

Reported by:	dim
Fixes:	522083ffbd ("kern: tty: recanonicalize the buffer on [...]")
This commit is contained in:
Kyle Evans 2024-01-24 13:36:26 -06:00
parent 8b82f36f89
commit 5738d741fb
1 changed files with 11 additions and 11 deletions
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22
sys/kern/tty_inq.c
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@ -371,12 +371,9 @@ ttyinq_canonicalize_break(struct ttyinq *ti, const char *breakc)
/* Start just past the end... */
off = ti->ti_end;
canon = 0;
while (off > 0) {
if ((off % TTYINQ_DATASIZE) == 0)
tib = tib->tib_prev;
canon = ti->ti_begin;
while (off > ti->ti_begin) {
off--;
boff = off % TTYINQ_DATASIZE;
@ -384,20 +381,23 @@ ttyinq_canonicalize_break(struct ttyinq *ti, const char *breakc)
canon = off + 1;
break;
}
if (off != ti->ti_begin && boff == 0)
tib = tib->tib_prev;
}
MPASS(canon > 0 || off == 0);
MPASS(canon > ti->ti_begin || off == ti->ti_begin);
/*
* We should only be able to hit bcanon == 0 if we walked everything we
* have and didn't find any of the break characters, so if bcanon == 0
* then tib is already the correct block and we should avoid touching
* it.
* We should only be able to hit canon == ti_begin if we walked
* everything we have and didn't find any of the break characters, so
* if canon == ti_begin then tib is already the correct block and we
* should avoid touching it.
*
* For all other scenarios, if canon lies on a block boundary then tib
* has already advanced to the previous block.
*/
if (canon != 0 && (canon % TTYINQ_DATASIZE) == 0)
if (canon != ti->ti_begin && (canon % TTYINQ_DATASIZE) == 0)
tib = tib->tib_next;
ti->ti_linestart = ti->ti_reprint = canon;
ti->ti_startblock = ti->ti_reprintblock = tib;