linux-kernel - [PATCH] OMAP: DSS2: OMAPFB: fix potential GPF

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Date:   Sat, 26 Jun 2021 01:33:23 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     gustavoars@...nel.org, sam@...nborg.org, tomi.valkeinen@...com
Cc:     linux-omap@...r.kernel.org, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Pavel Skripkin <paskripkin@...il.com>
Subject: [PATCH] OMAP: DSS2: OMAPFB: fix potential GPF

In case of allocation failures, all code paths was jumping
to this code:

err:
	kfree(fbi);
	kfree(var);
	kfree(fbops);

	return r;

Since all 3 pointers placed on stack and don't initialized, they
will be filled with some random values, which leads to
deferencing random pointers in kfree(). Fix it by rewriting
error handling path.

Fixes: 897044e99e43 ("OMAP: DSS2: OMAPFB: Reduce stack usage")
Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
---
 .../video/fbdev/omap2/omapfb/omapfb-main.c    | 21 +++++++++----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/omapfb-main.c b/drivers/video/fbdev/omap2/omapfb/omapfb-main.c
index a3decc7fadde..6a302138ebeb 100644
--- a/drivers/video/fbdev/omap2/omapfb/omapfb-main.c
+++ b/drivers/video/fbdev/omap2/omapfb/omapfb-main.c
@@ -2025,21 +2025,19 @@ static int omapfb_mode_to_timings(const char *mode_str,
 	fbops = NULL;
 
 	fbi = kzalloc(sizeof(*fbi), GFP_KERNEL);
-	if (fbi == NULL) {
-		r = -ENOMEM;
-		goto err;
-	}
+	if (fbi == NULL)
+		return -ENOMEM;
 
 	var = kzalloc(sizeof(*var), GFP_KERNEL);
 	if (var == NULL) {
 		r = -ENOMEM;
-		goto err;
+		goto err_var;
 	}
 
 	fbops = kzalloc(sizeof(*fbops), GFP_KERNEL);
 	if (fbops == NULL) {
 		r = -ENOMEM;
-		goto err;
+		goto err_fbops;
 	}
 
 	fbi->fbops = fbops;
@@ -2047,7 +2045,7 @@ static int omapfb_mode_to_timings(const char *mode_str,
 	r = fb_find_mode(var, fbi, mode_str, NULL, 0, NULL, 24);
 	if (r == 0) {
 		r = -EINVAL;
-		goto err;
+		goto err_find;
 	}
 
 	if (display->driver->get_timings) {
@@ -2088,11 +2086,12 @@ static int omapfb_mode_to_timings(const char *mode_str,
 
 	r = 0;
 
-err:
-	kfree(fbi);
-	kfree(var);
+err_find:
 	kfree(fbops);
-
+err_fbops:
+	kfree(var);
+err_var:
+	kfree(fbi);
 	return r;
 }
 
-- 
2.32.0