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

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Message-Id: <20220730034923.25500-1-mailmesebin00@gmail.com>
Date:   Sat, 30 Jul 2022 09:16:58 +0530
From:   Sebin Sebastian <mailmesebin00@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     mailmesebin00@...il.com, 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>, Evan Quan <evan.quan@....com>,
        Tom St Denis <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