2018-05-07 10:01:26

by Jens Wiklander

Subject: [PATCH] tee: shm: fix use-after-free via temporarily dropped reference

From: Jann Horn <[email protected]>

Bump the file's refcount before moving the reference into the fd table,
not afterwards. The old code could drop the file's refcount to zero for a
short moment before calling get_file() via get_dma_buf().

This code can only be triggered on ARM systems that use Linaro's OP-TEE.

Fixes: 967c9cca2cc5 ("tee: generic TEE subsystem")
Signed-off-by: Jann Horn <[email protected]>
Signed-off-by: Jens Wiklander <[email protected]>
---
drivers/tee/tee_shm.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index 556960a1bab3..07d3be6f0780 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -360,9 +360,10 @@ int tee_shm_get_fd(struct tee_shm *shm)
if (!(shm->flags & TEE_SHM_DMA_BUF))
return -EINVAL;

+ get_dma_buf(shm->dmabuf);
fd = dma_buf_fd(shm->dmabuf, O_CLOEXEC);
- if (fd >= 0)
- get_dma_buf(shm->dmabuf);
+ if (fd < 0)
+ dma_buf_put(shm->dmabuf);
return fd;
}

--
2.17.0

2018-05-07 14:56:19

by Volodymyr Babchuk

Subject: Re: [Tee-dev] [PATCH] tee: shm: fix use-after-free via temporarily dropped reference

Hi Jens,

On 7 May 2018 at 12:58, Jens Wiklander <[email protected]> wrote:
> From: Jann Horn <[email protected]>
>
> Bump the file's refcount before moving the reference into the fd table,
> not afterwards. The old code could drop the file's refcount to zero for a
> short moment before calling get_file() via get_dma_buf().
>
> This code can only be triggered on ARM systems that use Linaro's OP-TEE.
>
> Fixes: 967c9cca2cc5 ("tee: generic TEE subsystem")
> Signed-off-by: Jann Horn <[email protected]>
> Signed-off-by: Jens Wiklander <[email protected]>
Reviewed-by: Volodymyr Babchuk <[email protected]>

--
WBR Volodymyr Babchuk aka lorc [+380976646013]
mailto: [email protected]