When one process is trying to duplicate RO handle while other process is
trying to free the same RO handle, then race can occur and second
process can decrement the dma-buf's refcount and it may reach to 0. The
first process can then call get_dma_buf on it, leading to NULL pointer
dereference and ultimately to kernel panic. Fix this by taking an extra
dma-buf refcount before duplicating the handle and then decrease it once
duplication is completed.
Bug 3991243
Change-Id: I99901ce19d8a5d23c5192cb10a17efd2ebaf9d3a
Signed-off-by: Ketan Patil <ketanp@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvidia/+/2865519
Reviewed-by: svc_kernel_abi <svc_kernel_abi@nvidia.com>
Reviewed-by: svcacv <svcacv@nvidia.com>
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>
GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com>
There is a potential data race for RO dma-buf in the following scenario:
------------------------------------------------------------------
Process 1 | Process 2 | Process 3 |
------------------------------------------------------------------|
AllocAttr handle H1 | | |
MemMap (H1) | | |
AllocAttr(H2) | | |
MemMap(H2) | | |
id1 = GetSciIpcId(H1)| | |
id2 = GetSciIpcId(H2)|H3=HandleFromSciIpcId | |
id3 = GetSciIpcId(H1)| (id1, RO) |H4=HandleFromSciIpcId|
MemUnmap(H2) |QueryHandlePararms(H3)|(id2, RO) |
MemUnmap(H1) |MemMap(H3) |QueryHandleParams(H4)|
HandleFree(H2) |MemUnmap(H3) |MemMap(H4) |
HandleFree(H1) |HandleFree(H3) |H5=HandleFromSciIpcId|
| |(id3, RO) |
| |QueryHandleParams(H5)|
| |MemMap(H5) |
| |MemUnmap(H4) |
| |MemUnmap(H5) |
| |HandleFree(H4) |
| |HandleFree(H5) |
-------------------------------------------------------------------
The race is happening between the HandleFree(H3) in process 2 and
HandleFromSciIpcId(id3, RO) in process 3. Process 2 tries to free the
H3, and function nvmap_free_handle decrements the RO dma-buf's counter,
so that it reaches 0, but nvmap_dmabuf_release is not called immediately
because of which the process 3 get's false value for the following check
if (is_ro && h->dmabuf_ro == NULL)
It results in calling nvmap_duplicate_handle and then meanwhile function
nvmap_dmabuf_release is called and it makes h->dmabuf_ro to NULL. Hence
get_dma_buf fails with null pointer dereference error.
Fix this issue with following approach:
- Before using dmabuf_ro, take the handle->lock, then check if it is not
NULL.
- If not NULL, then call get_file_rcu on the file associated with RO
dma-buf and check return value.
- If return value is false, then dma-buf's ref counter is zero and it is
going away. So wait until dmabuf_ro is set to NULL; and then create a
new dma-buf for RO.
- Otherwise, use the existing RO dma-buf and decrement the refcount
taken with get_file_rcu.
Bug 3741751
Change-Id: I8987efebc476a794b240ca968b7915b4263ba664
Signed-off-by: Ketan Patil <ketanp@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvidia/+/2850394
Reviewed-by: svcacv <svcacv@nvidia.com>
Reviewed-by: svc_kernel_abi <svc_kernel_abi@nvidia.com>
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: Krishna Reddy <vdumpa@nvidia.com>
GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com>
