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pipe: Fix bogus dereference in iov_iter_alignment()

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We cannot look at 'i->pipe' unless we know the iter is a pipe. Move the
ring_size load to a branch in iov_iter_alignment() where we've already
checked the iter is a pipe to avoid bogus dereference.

Reported-by: syzbot+bea68382bae9490e7dd6@syzkaller.appspotmail.com
Fixes: 8cefc107ca ("pipe: Use head and tail pointers for the ring, not cursor and length")
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jan Kara 2019-12-16 11:54:32 +01:00 committed by Al Viro
parent e42617b825
commit e0ff126ee7
1 changed files with 2 additions and 1 deletions
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3
lib/iov_iter.c
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@ -1222,11 +1222,12 @@ EXPORT_SYMBOL(iov_iter_discard);
unsigned long iov_iter_alignment(const struct iov_iter *i)
{
unsigned int p_mask = i->pipe->ring_size - 1;
unsigned long res = 0;
size_t size = i->count;
if (unlikely(iov_iter_is_pipe(i))) {
unsigned int p_mask = i->pipe->ring_size - 1;
if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask]))
return size | i->iov_offset;
return size;