linux-kernel - [PATCH] tty: vt: Check for NULL pointer after calling kzalloc

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Date:   Fri, 21 Jan 2022 14:53:20 +0800
From:   Jiasheng Jiang <jiasheng@...as.ac.cn>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        jcmvbkbc@...il.com, dsterba@...e.com, johan@...nel.org,
        dankamongmen@...il.com, penguin-kernel@...ove.SAKURA.ne.jp,
        igormtorrente@...il.com
Cc:     linux-kernel@...r.kernel.org, Jiasheng Jiang <jiasheng@...as.ac.cn>
Subject: [PATCH] tty: vt: Check for NULL pointer after calling kzalloc

As the potential failure of the allocation, the kzalloc() will return
NULL pointer.
Therefore, it should be better to check it in order to avoid the
dereference of the NULL pointer.
When it fails, we should free all the allocated memory and return error
number.
To make the code more clear, I use the 'err_free', like how
vc_allocate() deals with the allocation failure.

Fixes: a5f4f52e8211 ("vt: use kzalloc() instead of the bootmem allocator")
Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
---
 drivers/tty/vt/vt.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f8c87c4d7399..343fa6fffc18 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3519,11 +3519,17 @@ static int __init con_init(void)
 
 	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
 		vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
+		if (!vc)
+			goto err_free;
+
 		INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
 		tty_port_init(&vc->port);
 		visual_init(vc, currcons, 1);
 		/* Assuming vc->vc_{cols,rows,screenbuf_size} are sane here. */
 		vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
+		if (!vc->vc_screenbuf)
+			goto err_free_vc;
+
 		vc_init(vc, vc->vc_rows, vc->vc_cols,
 			currcons || !vc->vc_sw->con_save_screen);
 	}
@@ -3545,6 +3551,19 @@ static int __init con_init(void)
 	register_console(&vt_console_driver);
 #endif
 	return 0;
+err_free_vc:
+	visual_deinit(vc);
+	kfree(vc);
+	vc_cons[currcons].d = NULL;
+err_free:
+	for (i = 0; i < currcons; i++) {
+		kfree(vc_cons[currcons].d->vc_screenbuf);
+		visual_deinit(vc_cons[currcons].d);
+		kfree(vc_cons[currcons].d);
+		vc_cons[currcons].d = NULL;
+	}
+	console_unlock();
+	return -ENOMEM;
 }
 console_initcall(con_init);
 
-- 
2.25.1