Re: [PATCH] drm/amdkfd: Fix potential NULL pointer dereference

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Am 2022-04-04 um 18:21 schrieb Grigory Vasilyev:
In the amdgpu_amdkfd_get_xgmi_bandwidth_mbytes function,
the peer_adev pointer can be NULL and is passed to amdgpu_xgmi_get_num_links.

In amdgpu_xgmi_get_num_links, peer_adev pointer is dereferenced
without any checks: peer_adev->gmc.xgmi.node_id .

What's worse, peer_adev is uninitialized with an undefined value if src is NULL. So that code was definitely bogus.

However, I think your patch will result in incorrect results. Currently amdgpu_amdkfd_get_xgmi_bandwidth is always called with is_min=true if src==NULL, and with is_min=false if src!=NULL. The intention is, that we assume a single XGMI link in the case that src==NULL. That means the is_min parameter is redundant. What we should do instead is, assume that num_links==1 if src==NULL, and drop the is_min parameter.

That would keep things working the way they do now, and prevent potential problems in the future.

Regards,
  Felix



Signed-off-by: Grigory Vasilyev <h0tc0d3@xxxxxxxxx>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c | 5 ++---
  1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
index be1a55f8b8c5..1a1006b18016 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c
@@ -541,11 +541,10 @@ int amdgpu_amdkfd_get_xgmi_bandwidth_mbytes(struct amdgpu_device *dst,
  	struct amdgpu_device *adev = dst, *peer_adev;
  	int num_links;
- if (adev->asic_type != CHIP_ALDEBARAN)
+	if (!src || adev->asic_type != CHIP_ALDEBARAN)
  		return 0;
- if (src)
-		peer_adev = src;
+	peer_adev = src;
/* num links returns 0 for indirect peers since indirect route is unknown. */
  	num_links = is_min ? 1 : amdgpu_xgmi_get_num_links(adev, peer_adev);



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