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n_tty: Fix echo overrun tail computation 

Commit cbfd0340ae,
'n_tty: Process echoes in blocks', introduced an error when
consuming the echo buffer tail to prevent buffer overrun, where
the incorrect operation code byte is checked to determine how
far to advance the tail to the next echo byte.

Check the correct byte for the echo operation code byte.

Cc: <stable@vger.kernel.org> # 3.12.x : c476f65 tty: incorrect test of echo_buf() result for ECHO_OP_START
Cc: <stable@vger.kernel.org> # 3.12.x
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-11-08 09:42:18 -05:00 committed by Greg Kroah-Hartman
parent 42458f41d0
commit 6f2225363c
1 changed files with 1 additions and 1 deletions
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2
drivers/tty/n_tty.c
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@ -768,7 +768,7 @@ static size_t __process_echoes(struct tty_struct *tty)
* data at the tail to prevent a subsequent overrun */
while (ldata->echo_commit - tail >= ECHO_DISCARD_WATERMARK) {
if (echo_buf(ldata, tail) == ECHO_OP_START) {
if (echo_buf(ldata, tail) == ECHO_OP_ERASE_TAB)
if (echo_buf(ldata, tail + 1) == ECHO_OP_ERASE_TAB)
tail += 3;
else
tail += 2;