From bb765d1c331f62b59049d35607ed2e365802bef9 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 4 Apr 2018 21:03:21 +0200 Subject: [PATCH 1/2] tee: shm: fix use-after-free via temporarily dropped reference 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 Signed-off-by: Jens Wiklander --- 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; } From ab9d3db5b320a052452b9cd035599ee3c84bbee9 Mon Sep 17 00:00:00 2001 From: Etienne Carriere Date: Sun, 29 Apr 2018 14:22:29 +0200 Subject: [PATCH 2/2] tee: check shm references are consistent in offset/size This change prevents userland from referencing TEE shared memory outside the area initially allocated by its owner. Prior this change an application could not reference or access memory it did not own but it could reference memory not explicitly allocated by owner but still allocated to the owner due to the memory allocation granule. Reported-by: Alexandre Jutras Signed-off-by: Etienne Carriere Signed-off-by: Jens Wiklander --- drivers/tee/tee_core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c index 0124a91c8d71..dd46b758852a 100644 --- a/drivers/tee/tee_core.c +++ b/drivers/tee/tee_core.c @@ -238,6 +238,17 @@ static int params_from_user(struct tee_context *ctx, struct tee_param *params, if (IS_ERR(shm)) return PTR_ERR(shm); + /* + * Ensure offset + size does not overflow offset + * and does not overflow the size of the referred + * shared memory object. + */ + if ((ip.a + ip.b) < ip.a || + (ip.a + ip.b) > shm->size) { + tee_shm_put(shm); + return -EINVAL; + } + params[n].u.memref.shm_offs = ip.a; params[n].u.memref.size = ip.b; params[n].u.memref.shm = shm;