linux-kernel - Re: [PATCH -next] drm/amdgpu: double free error and freeing uninitialized null pointer

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Date:   Tue, 12 Jul 2022 12:14:27 -0300
From:   André Almeida <andrealmeid@...lia.com>
To:     Sebin Sebastian <mailmesebin00@...il.com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nirmoy Das <nirmoy.das@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        Tom St Denis <tom.stdenis@....com>,
        Evan Quan <evan.quan@....com>,
        Somalapuram Amaranath <Amaranath.Somalapuram@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] drm/amdgpu: double free error and freeing
 uninitialized null pointer

Hi Sebin,

Às 10:29 de 10/07/22, Sebin Sebastian escreveu:
> Fix two coverity warning's double free and and an uninitialized pointer
> read. Both tmp and new are pointing at same address and both are freed
> which leads to double free. Freeing tmp in the condition after new is
> assigned with new address fixes the double free issue. new is not
> initialized to null which also leads to a free on an uninitialized
> pointer.
> Coverity issue: 1518665 (uninitialized pointer read)
> 		1518679 (double free)

What are those numbers?

> 
> Signed-off-by: Sebin Sebastian <mailmesebin00@...il.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> index f3b3c688e4e7..d82fe0e1b06b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> @@ -1660,7 +1660,7 @@ 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 {
> @@ -1692,17 +1692,19 @@ static ssize_t amdgpu_reset_dump_register_list_write(struct file *f,
>  		goto error_free;
>  	}

If the `if (!new) {` above this line is true, will be tmp freed?

>  	ret = down_write_killable(&adev->reset_domain->sem);
> -	if (ret)
> +	if (ret) {
> +		kfree(tmp);
>  		goto error_free;
> +	}
>  
>  	swap(adev->reset_dump_reg_list, tmp);
>  	swap(adev->reset_dump_reg_value, new);
>  	adev->num_regs = i;
>  	up_write(&adev->reset_domain->sem);
> +	kfree(tmp);
>  	ret = size;
>  
>  error_free:
> -	kfree(tmp);
>  	kfree(new);
>  	return ret;
>  }