From c77569d2f3ef7844ee4ac7005a57da6898b302a8 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 22 Nov 2013 07:16:25 -0500 Subject: [PATCH] n_tty: Fix 4096-byte canonical reads Although the maximum allowable canonical line is specified to be 255 bytes (MAX_CANON), the practical limit has actually been the size of the line discipline read buffer (N_TTY_BUF_SIZE == 4096). Commit 32f13521ca68bc624ff6effc77f308a52b038bf0, n_tty: Line copy to user buffer in canonical mode, limited the line copy to 4095 bytes. With a completely full line discipline read buffer and a userspace buffer > 4095, _no_ data was copied, and the read() syscall returned 0, indicating EOF. Fix the interval arithmetic to compute the correct number of bytes to copy to userspace in the range [1..4096]. Cc: # 3.12.x Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_tty.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index d8a779d..c222a56 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1998,7 +1998,10 @@ static int canon_copy_from_read_buf(struct tty_struct *tty, found = 1; size = N_TTY_BUF_SIZE - tail; - n = (found + eol + size) & (N_TTY_BUF_SIZE - 1); + n = eol - tail; + if (n > 4096) + n += 4096; + n += found; c = n; if (found && read_buf(ldata, eol) == __DISABLED_CHAR) { -- 2.7.4