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Date:   Wed, 22 May 2019 20:19:08 +0800
From:   Gen Zhang <blackgod016574@gmail.com>
To:     Nicolas Pitre <nico@fluxnic.net>
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH v3] vt: Fix a missing-check bug in drivers/tty/vt/vt.c
Message-ID: <20190522121908.GA6772@zhanggen-UX430UQ>
References: <20190521022940.GA4858@zhanggen-UX430UQ>
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 <20190521040019.GD5263@zhanggen-UX430UQ>
 <nycvar.YSQ.7.76.1905210022050.1558@knanqh.ubzr>
 <20190521073901.GF5263@zhanggen-UX430UQ>
 <nycvar.YSQ.7.76.1905212218090.1558@knanqh.ubzr>
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In function con_init(), the pointer variable vc_cons[currcons].d, vc and
vc->vc_screenbuf is allocated a memory space via kzalloc(). And they are
used in the following codes.
However, when there is a memory allocation error, kzalloc() can fail.
Thus null pointer (vc_cons[currcons].d, vc and vc->vc_screenbuf)
dereference may happen. And it will cause the kernel to crash. Therefore,
we should check 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@gmail.com>

---
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);
 
---