linux-kernel - [PATCH v3] vt: Fix a missing-check bug in con

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Date:   Tue, 28 May 2019 08:45:29 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     gregkh@...uxfoundation.org, jslaby@...e.com, nico@...xnic.net,
        kilobyte@...band.pl, textshell@...uujin.de, mpatocka@...hat.com,
        daniel.vetter@...ll.ch
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH v3] vt: Fix a missing-check bug in con_init()

In function con_init(), the pointer variable vc_cons[currcons].d, vc and
vc->vc_screenbuf is allocated by kzalloc(). And they are used in the 
following codes. However, kzalloc() returns NULL when fails, and null 
pointer dereference may happen. And it will cause the kernel to crash. 
Therefore, we should check the return value and handle the error.

Further, since the allcoation is in a loop, we should free all the 
allocated memory in a loop.

Signed-off-by: Gen Zhang <blackgod016574@...il.com>
Reviewed-by: Nicolas Pitre <nico@...xnic.net>
---
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index fdd12f8..d50f68f 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3350,10 +3350,14 @@ 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 fail1;
 		INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
 		tty_port_init(&vc->port);
 		visual_init(vc, currcons, 1);
 		vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
+		if (!vc->vc_screenbuf)
+			goto fail2;
 		vc_init(vc, vc->vc_rows, vc->vc_cols,
 			currcons || !vc->vc_sw->con_save_screen);
 	}
@@ -3375,6 +3379,16 @@ static int __init con_init(void)
 	register_console(&vt_console_driver);
 #endif
 	return 0;
+fail1:
+	while (currcons > 0) {
+		currcons--;
+		kfree(vc_cons[currcons].d->vc_screenbuf);
+fail2:
+		kfree(vc_cons[currcons].d);
+		vc_cons[currcons].d = NULL;
+	}
+	console_unlock();
+	return -ENOMEM;
 }
 console_initcall(con_init);
 
---