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n_tty: check for negative and zero space return from tty_write_room 

The return from tty_write_room could potentially be negative if
a tty write_room driver returns an error number (not that any seem
to do). Rather than just check for a zero return, also check for
a -ve return. This avoids the unsigned nr being set to a large unsigned
value on the assignment from variable space and can lead to overflowing
the buffer buf.  Better to be safe than assume all write_room
implementations in tty drivers are going to do the right thing.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Colin Ian King 2019-03-30 00:46:28 +00:00 committed by Greg Kroah-Hartman
parent f16aa97d3f
commit 9ef8927f45
1 changed files with 2 additions and 2 deletions
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4
drivers/tty/n_tty.c
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@ -550,9 +550,9 @@ static ssize_t process_output_block(struct tty_struct *tty,
mutex_lock(&ldata->output_lock);
space = tty_write_room(tty);
if (!space) {
if (space <= 0) {
mutex_unlock(&ldata->output_lock);
return 0;
return space;
}
if (nr > space)
nr = space;