[ Upstream commit 33927f3d0e ]
As soon as we'd inserted a file reference into descriptor table, another
thread could close it. That's fine for the case when all we are doing is
returning that descriptor to userland (it's a race, but it's a userland
race and there's nothing the kernel can do about it). However, if we
follow fd_install() with any kind of access to objects that would be
destroyed on close (be it the struct file itself or anything destroyed
by its ->release()), we have a UAF.
dma_buf_fd() is a combination of reserving a descriptor and fd_install().
habanalabs export_dmabuf() calls it and then proceeds to access the
objects destroyed on close. In particular, it grabs an extra reference to
another struct file that will be dropped as part of ->release() for ours;
that "will be" is actually "might have already been".
Fix that by reserving descriptor before anything else and do fd_install()
only when everything had been set up. As a side benefit, we no longer
have the failure exit with file already created, but reference to
underlying file (as well as ->dmabuf_export_cnt, etc.) not grabbed yet;
unlike dma_buf_fd(), fd_install() can't fail.
Fixes: db1a8dd916 ("habanalabs: add support for dma-buf exporter")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
40deceb38f