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authorPeter Hurley <peter@hurleysoftware.com>2015-01-16 15:05:39 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-04-19 10:11:08 +0200
commit4a673d7acafe13f7ff23dd292ff185623517bf2c (patch)
treefcc7dd7c96b9800f827791e1ac956120c235370c /drivers
parent9185aae67a63b81187f28225137595208895b5c1 (diff)
downloadlinux-linaro-stable-4a673d7acafe13f7ff23dd292ff185623517bf2c.tar.gz
n_tty: Fix read buffer overwrite when no newline
commit fb5ef9e7da39968fec6d6f37f20a23d23740c75e upstream. In canon mode, the read buffer head will advance over the buffer tail if the input > 4095 bytes without receiving a line termination char. Discard additional input until a line termination is received. Before evaluating for overflow, the 'room' value is normalized for I_PARMRK and 1 byte is reserved for line termination (even in !icanon mode, in case the mode is switched). The following table shows the transform: actual buffer | 'room' value before overflow calc space avail | !I_PARMRK | I_PARMRK -------------------------------------------------- 0 | -1 | -1 1 | 0 | 0 2 | 1 | 0 3 | 2 | 0 4+ | 3 | 1 When !icanon or when icanon and the read buffer contains newlines, normalized 'room' values of -1 and 0 are clamped to 0, and 'overflow' is 0, so read_head is not adjusted and the input i/o loop exits (setting no_room if called from flush_to_ldisc()). No input is discarded since the reader does have input available to read which ensures forward progress. When icanon and the read buffer does not contain newlines and the normalized 'room' value is 0, then overflow and room are reset to 1, so that the i/o loop will process the next input char normally (except for parity errors which are ignored). Thus, erasures, signalling chars, 7-bit mode, etc. will continue to be handled properly. If the input char processed was not a line termination char, then the canon_head index will not have advanced, so the normalized 'room' value will now be -1 and 'overflow' will be set, which indicates the read_head can safely be reset, effectively erasing the last char processed. If the input char processed was a line termination, then the canon_head index will have advanced, so 'overflow' is cleared to 0, the read_head is not reset, and 'room' is cleared to 0, which exits the i/o loop (because the reader now have input available to read which ensures forward progress). Note that it is possible for a line termination to be received, and for the reader to copy the line to the user buffer before the input i/o loop is ready to process the next input char. This is why the i/o loop recomputes the room/overflow state with every input char while handling overflow. Finally, if the input data was processed without receiving a line termination (so that overflow is still set), the pty driver must receive a write wakeup. A pty writer may be waiting to write more data in n_tty_write() but without unthrottling here that wakeup will not arrive, and forward progress will halt. (Normally, the pty writer is woken when the reader reads data out of the buffer and more space become available). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> (backported from commit fb5ef9e7da39968fec6d6f37f20a23d23740c75e) Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/tty/n_tty.c106
1 files changed, 79 insertions, 27 deletions
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 850e232d086e..8ab46ad40f28 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -247,8 +247,6 @@ static void n_tty_write_wakeup(struct tty_struct *tty)
static void n_tty_check_throttle(struct tty_struct *tty)
{
- if (tty->driver->type == TTY_DRIVER_TYPE_PTY)
- return;
/*
* Check the remaining room for the input canonicalization
* mode. We don't want to throttle the driver if we're in
@@ -1512,23 +1510,6 @@ n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
n_tty_receive_char_flagged(tty, c, flag);
}
-/**
- * n_tty_receive_buf - data receive
- * @tty: terminal device
- * @cp: buffer
- * @fp: flag buffer
- * @count: characters
- *
- * Called by the terminal driver when a block of characters has
- * been received. This function must be called from soft contexts
- * not from interrupt context. The driver is responsible for making
- * calls one at a time and in order (or using flush_to_ldisc)
- *
- * n_tty_receive_buf()/producer path:
- * claims non-exclusive termios_rwsem
- * publishes read_head and canon_head
- */
-
static void
n_tty_receive_buf_real_raw(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
@@ -1684,24 +1665,85 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
}
}
+/**
+ * n_tty_receive_buf_common - process input
+ * @tty: device to receive input
+ * @cp: input chars
+ * @fp: flags for each char (if NULL, all chars are TTY_NORMAL)
+ * @count: number of input chars in @cp
+ *
+ * Called by the terminal driver when a block of characters has
+ * been received. This function must be called from soft contexts
+ * not from interrupt context. The driver is responsible for making
+ * calls one at a time and in order (or using flush_to_ldisc)
+ *
+ * Returns the # of input chars from @cp which were processed.
+ *
+ * In canonical mode, the maximum line length is 4096 chars (including
+ * the line termination char); lines longer than 4096 chars are
+ * truncated. After 4095 chars, input data is still processed but
+ * not stored. Overflow processing ensures the tty can always
+ * receive more input until at least one line can be read.
+ *
+ * In non-canonical mode, the read buffer will only accept 4095 chars;
+ * this provides the necessary space for a newline char if the input
+ * mode is switched to canonical.
+ *
+ * Note it is possible for the read buffer to _contain_ 4096 chars
+ * in non-canonical mode: the read buffer could already contain the
+ * maximum canon line of 4096 chars when the mode is switched to
+ * non-canonical.
+ *
+ * n_tty_receive_buf()/producer path:
+ * claims non-exclusive termios_rwsem
+ * publishes commit_head or canon_head
+ */
static int
n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count, int flow)
{
struct n_tty_data *ldata = tty->disc_data;
- int room, n, rcvd = 0;
+ int room, n, rcvd = 0, overflow;
down_read(&tty->termios_rwsem);
while (1) {
- room = receive_room(tty);
+ /*
+ * When PARMRK is set, each input char may take up to 3 chars
+ * in the read buf; reduce the buffer space avail by 3x
+ *
+ * If we are doing input canonicalization, and there are no
+ * pending newlines, let characters through without limit, so
+ * that erase characters will be handled. Other excess
+ * characters will be beeped.
+ *
+ * paired with store in *_copy_from_read_buf() -- guarantees
+ * the consumer has loaded the data in read_buf up to the new
+ * read_tail (so this producer will not overwrite unread data)
+ */
+ size_t tail = ldata->read_tail;
+
+ room = N_TTY_BUF_SIZE - (ldata->read_head - tail);
+ if (I_PARMRK(tty))
+ room = (room + 2) / 3;
+ room--;
+ if (room <= 0) {
+ overflow = ldata->icanon && ldata->canon_head == tail;
+ if (overflow && room < 0)
+ ldata->read_head--;
+ room = overflow;
+ ldata->no_room = flow && !room;
+ } else
+ overflow = 0;
+
n = min(count, room);
- if (!n) {
- if (flow && !room)
- ldata->no_room = 1;
+ if (!n)
break;
- }
- __receive_buf(tty, cp, fp, n);
+
+ /* ignore parity errors if handling overflow */
+ if (!overflow || !fp || *fp != TTY_PARITY)
+ __receive_buf(tty, cp, fp, n);
+
cp += n;
if (fp)
fp += n;
@@ -1710,7 +1752,17 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp,
}
tty->receive_room = room;
- n_tty_check_throttle(tty);
+
+ /* Unthrottle if handling overflow on pty */
+ if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
+ if (overflow) {
+ tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
+ tty_unthrottle_safe(tty);
+ __tty_set_flow_change(tty, 0);
+ }
+ } else
+ n_tty_check_throttle(tty);
+
up_read(&tty->termios_rwsem);
return rcvd;