Commit 3342ff26 authored by Linus Torvalds's avatar Linus Torvalds

tty: protect tty_write from odd low-level tty disciplines

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
9bb48c82 ("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: 9bb48c82 ("tty: implement write_iter")
Debugged-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2c405d1a
......@@ -962,11 +962,14 @@ 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;
......
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