From 4d0ed18277cc6f07513ee0b04475f19cd69e75ef Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Tue, 10 Dec 2013 17:12:02 -0500 Subject: [PATCH] n_tty: Fix buffer overruns with larger-than-4k pastes readline() inadvertently triggers an error recovery path when pastes larger than 4k overrun the line discipline buffer. The error recovery path discards input when the line discipline buffer is full and operating in canonical mode and no newline has been received. Because readline() changes the termios to non-canonical mode to read the line char-by-char, the line discipline buffer can become full, and then when readline() restores termios back to canonical mode for the caller, the now-full line discipline buffer triggers the error recovery. When changing termios from non-canon to canon mode and the read buffer contains data, simulate an EOF push _without_ the DISABLED_CHAR in the read buffer. Importantly for the readline() problem, the termios can be changed back to non-canonical mode without changes to the read buffer occurring; ie., as if the previous termios change had not happened (as long as no intervening read took place). Preserve existing userspace behavior which allows '\0's already received in non-canon mode to be read as '\0's in canon mode (rather than trigger add'l EOF pushes or an actual EOF). Patch based on original proposal and discussion here https://bugzilla.kernel.org/show_bug.cgi?id=55991 by Stas Sergeev Reported-by: Margarita Manterola Cc: Maximiliano Curia Cc: Pavel Machek Cc: Arkadiusz Miskiewicz Acked-by: Stas Sergeev Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_tty.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index fdc2ecde5ac2..961e6a996dff 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -104,6 +104,7 @@ struct n_tty_data { /* must hold exclusive termios_rwsem to reset these */ unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1; + unsigned char push:1; /* shared by producer and consumer */ char read_buf[N_TTY_BUF_SIZE]; @@ -341,6 +342,7 @@ static void reset_buffer_flags(struct n_tty_data *ldata) ldata->erasing = 0; bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE); + ldata->push = 0; } static void n_tty_packet_mode_flush(struct tty_struct *tty) @@ -1745,7 +1747,16 @@ static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old) if (!old || (old->c_lflag ^ tty->termios.c_lflag) & ICANON) { bitmap_zero(ldata->read_flags, N_TTY_BUF_SIZE); - ldata->line_start = ldata->canon_head = ldata->read_tail; + ldata->line_start = ldata->read_tail; + if (!L_ICANON(tty) || !read_cnt(ldata)) { + ldata->canon_head = ldata->read_tail; + ldata->push = 0; + } else { + set_bit((ldata->read_head - 1) & (N_TTY_BUF_SIZE - 1), + ldata->read_flags); + ldata->canon_head = ldata->read_head; + ldata->push = 1; + } ldata->erasing = 0; ldata->lnext = 0; } @@ -1951,6 +1962,12 @@ static int copy_from_read_buf(struct tty_struct *tty, * it copies one line of input up to and including the line-delimiting * character into the user-space buffer. * + * NB: When termios is changed from non-canonical to canonical mode and + * the read buffer contains data, n_tty_set_termios() simulates an EOF + * push (as if C-d were input) _without_ the DISABLED_CHAR in the buffer. + * This causes data already processed as input to be immediately available + * as input although a newline has not been received. + * * Called under the atomic_read_lock mutex * * n_tty_read()/consumer path: @@ -1997,7 +2014,7 @@ static int canon_copy_from_read_buf(struct tty_struct *tty, n += found; c = n; - if (found && read_buf(ldata, eol) == __DISABLED_CHAR) { + if (found && !ldata->push && read_buf(ldata, eol) == __DISABLED_CHAR) { n--; eof_push = !n && ldata->read_tail != ldata->line_start; } @@ -2024,7 +2041,10 @@ static int canon_copy_from_read_buf(struct tty_struct *tty, ldata->read_tail += c; if (found) { - ldata->line_start = ldata->read_tail; + if (!ldata->push) + ldata->line_start = ldata->read_tail; + else + ldata->push = 0; tty_audit_push(tty); } return eof_push ? -EAGAIN : 0; -- 2.34.1