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commit 9b91b6b019fda817eb52f728eb9c79b3579760bc upstream.
There's possibility of an ABBA deadlock in case of a splice write to an
overlayfs file and a concurrent splice write to a corresponding real file.
The call chain for splice to an overlay file:
-> do_splice [takes sb_writers on overlay file]
-> do_splice_from
-> iter_file_splice_write [takes pipe->mutex]
-> vfs_iter_write
...
-> ovl_write_iter [takes sb_writers on real file]
And the call chain for splice to a real file:
-> do_splice [takes sb_writers on real file]
-> do_splice_from
-> iter_file_splice_write [takes pipe->mutex]
Syzbot successfully bisected this to commit 82a763e61e2b ("ovl: simplify
file splice").
Fix by reverting the write part of the above commit and by adding missing
bits from ovl_write_iter() into ovl_splice_write().
Fixes: 82a763e61e2b ("ovl: simplify file splice")
Reported-and-tested-by: syzbot+579885d1a9a833336209@syzkaller.appspotmail.com
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
c4461ca7a8