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

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Date:   Mon, 1 Aug 2022 01:28:06 +0000
From:   "Quan, Evan" <Evan.Quan@....com>
To:     Sebin Sebastian <mailmesebin00@...il.com>
CC:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nirmoy Das <nirmoy.das@....com>,
        "Lazar, Lijo" <Lijo.Lazar@....com>,
        "StDenis, Tom" <Tom.StDenis@....com>,
        "Somalapuram, Amaranath" <Amaranath.Somalapuram@....com>,
        André Almeida <andrealmeid@...lia.com>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCHv2 -next] drm/amdgpu: double free error and freeing
 uninitialized null pointer

[AMD Official Use Only - General]

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

> -----Original Message-----
> From: Sebin Sebastian <mailmesebin00@...il.com>
> Sent: Saturday, July 30, 2022 11:47 AM
> Cc: mailmesebin00@...il.com; Deucher, Alexander
> <Alexander.Deucher@....com>; Koenig, Christian
> <Christian.Koenig@....com>; Pan, Xinhui <Xinhui.Pan@....com>; David
> Airlie <airlied@...ux.ie>; Daniel Vetter <daniel@...ll.ch>; Nirmoy Das
> <nirmoy.das@....com>; Lazar, Lijo <Lijo.Lazar@....com>; Quan, Evan
> <Evan.Quan@....com>; StDenis, Tom <Tom.StDenis@....com>;
> Somalapuram, Amaranath <Amaranath.Somalapuram@....com>; André
> Almeida <andrealmeid@...lia.com>; amd-gfx@...ts.freedesktop.org; dri-
> devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
> 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@....com>
> Signed-off-by: Sebin Sebastian <mailmesebin00@...il.com>
> ---
> Changes in v2:
> Updated patch body as suggested by André Almeida
> <andrealmeid@...lia.com>
> Reworked to implement a check in error_free for fixing double free error
> as suggested by S. Amaranath <Amaranath.Somalapuram@....com>
> 
>  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