RE: [PATCHv2 -next] drm/amdgpu: double free error and freeing uninitialized null pointer

[Quan, Evan]

[AMD Official Use Only - General]

Reviewed-by: Evan Quan <evan.quan@xxxxxxx>

> -----Original Message-----
> From: Sebin Sebastian <mailmesebin00@xxxxxxxxx>
> Sent: Saturday, July 30, 2022 11:47 AM
> Cc: mailmesebin00@xxxxxxxxx; Deucher, Alexander
> <Alexander.Deucher@xxxxxxx>; Koenig, Christian
> <Christian.Koenig@xxxxxxx>; Pan, Xinhui <Xinhui.Pan@xxxxxxx>; David
> Airlie <airlied@xxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>; Nirmoy Das
> <nirmoy.das@xxxxxxx>; Lazar, Lijo <Lijo.Lazar@xxxxxxx>; Quan, Evan
> <Evan.Quan@xxxxxxx>; StDenis, Tom <Tom.StDenis@xxxxxxx>;
> Somalapuram, Amaranath <Amaranath.Somalapuram@xxxxxxx>; André
> Almeida <andrealmeid@xxxxxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-
> devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCHv2 -next] drm/amdgpu: double free error and freeing
> uninitialized null pointer
> 
> Fix a double free and an uninitialized pointer read error. Both tmp and
> new are pointing at same address and both are freed which leads to
> double free. Adding a check to verify if new and tmp are free in the
> error_free label fixes the double free issue. new is not initialized to
> null which also leads to a free on an uninitialized pointer.
> 
> Suggested by: S. Amaranath <Amaranath.Somalapuram@xxxxxxx>
> Signed-off-by: Sebin Sebastian <mailmesebin00@xxxxxxxxx>
> ---
> Changes in v2:
> Updated patch body as suggested by André Almeida
> <andrealmeid@xxxxxxxxxx>
> Reworked to implement a check in error_free for fixing double free error
> as suggested by S. Amaranath <Amaranath.Somalapuram@xxxxxxx>
> 
>  drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> index e2eec985adb3..cb00c7d6f50b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> @@ -1705,7 +1705,7 @@ static ssize_t
> amdgpu_reset_dump_register_list_write(struct file *f,
>  {
>  	struct amdgpu_device *adev = (struct amdgpu_device
> *)file_inode(f)->i_private;
>  	char reg_offset[11];
> -	uint32_t *new, *tmp = NULL;
> +	uint32_t *new = NULL, *tmp = NULL;
>  	int ret, i = 0, len = 0;
> 
>  	do {
> @@ -1747,7 +1747,8 @@ static ssize_t
> amdgpu_reset_dump_register_list_write(struct file *f,
>  	ret = size;
> 
>  error_free:
> -	kfree(tmp);
> +	if (tmp != new)
> +		kfree(tmp);
>  	kfree(new);
>  	return ret;
>  }
> --
> 2.34.1