From: Linus Torvalds torvalds@linux-foundation.org
commit 3342ff2698e9720f4040cc458a2744b2b32f5c3a upstream.
Al root-caused a new warning from syzbot to the ttyprintk tty driver returning a write count larger than the data the tty layer actually gave it. Which confused the tty write code mightily, and with the new iov_iter based code, caused a WARNING in iov_iter_revert().
syzbot correctly bisected the source of the new warning to commit 9bb48c82aced ("tty: implement write_iter"), but the oddity goes back much further, it just didn't get caught by anything before.
Reported-by: syzbot+3d2c27c2b7dc2a94814d@syzkaller.appspotmail.com Fixes: 9bb48c82aced ("tty: implement write_iter") Debugged-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/tty_io.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -963,11 +963,14 @@ static inline ssize_t do_tty_write( if (ret <= 0) break;
+ written += ret; + if (ret > size) + break; + /* FIXME! Have Al check this! */ if (ret != size) iov_iter_revert(from, size-ret);
- written += ret; count -= ret; if (!count) break;