linux-kernel - [PATCH] drm/ast: fix using freed memory

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Message-Id: <20220203152305.1846862-1-trix@redhat.com>
Date:   Thu,  3 Feb 2022 07:23:05 -0800
From:   trix@...hat.com
To:     airlied@...hat.com, tzimmermann@...e.de, airlied@...ux.ie,
        daniel@...ll.ch, nathan@...nel.org, ndesaulniers@...gle.com,
        maxime@...no.tech
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Tom Rix <trix@...hat.com>
Subject: [PATCH] drm/ast: fix using freed memory

From: Tom Rix <trix@...hat.com>

clang static analysis reports this problem
ast_mode.c:1235:3: warning: Use of memory after it is freed
  drm_connector_update_edid_property(&ast_connector->base, edid);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The second condition on

  if (!flags && ast_connector->i2c)

Means that the edid is not always set.  If the previous block
fails the freed edid value will be used.  So set edid to NULL
after freeing.

Fixes: 55dc449a7c60 ("drm/ast: Handle failed I2C initialization gracefully")
Signed-off-by: Tom Rix <trix@...hat.com>
---
 drivers/gpu/drm/ast/ast_mode.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index ab52efb15670e..9131dc8a1a2fc 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -1224,10 +1224,12 @@ static int ast_get_modes(struct drm_connector *connector)
 			return -ENOMEM;
 
 		flags = ast_dp501_read_edid(connector->dev, (u8 *)edid);
-		if (flags)
+		if (flags) {
 			ast->dp501_maxclk = ast_get_dp501_max_clk(connector->dev);
-		else
+		} else {
 			kfree(edid);
+			edid = NULL;
+		}
 	}
 	if (!flags && ast_connector->i2c)
 		edid = drm_get_edid(connector, &ast_connector->i2c->adapter);
-- 
2.26.3