linux-kernel - [PATCH] Revert "consolemap: Fix a memory leaking bug in drivers/tty/vt/consolemap.c"

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Date:   Tue, 4 Jun 2019 19:00:39 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     Gen Zhang <blackgod016574@...il.com>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] Revert "consolemap: Fix a memory leaking bug in
 drivers/tty/vt/consolemap.c"

This reverts commit 84ecc2f6eb1cb12e6d44818f94fa49b50f06e6ac.

con_insert_unipair() is working with a sparse 3-dimensional array:

- p->uni_pgdir[] is the top layer
- p1 points to a middle layer
- p2 points to a bottom layer

If it needs to allocate a new middle layer, and then fails to allocate
a new bottom layer, it would previously free only p2, and now it frees
both p1 and p2.  But since the new middle layer was already registered
in the top layer, it was not leaked.

However, if it looks up an *existing* middle layer and then fails to
allocate a bottom layer, it now frees both p1 and p2 but does *not*
free any other bottom layers under p1.  So it *introduces* a memory
leak.

The error path also cleared the wrong index in p->uni_pgdir[],
introducing a use-after-free.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/tty/vt/consolemap.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
index 79fcc96cc7c0..b28aa0d289f8 100644
--- a/drivers/tty/vt/consolemap.c
+++ b/drivers/tty/vt/consolemap.c
@@ -489,11 +489,7 @@ con_insert_unipair(struct uni_pagedir *p, u_short unicode, u_short fontpos)
 	p2 = p1[n = (unicode >> 6) & 0x1f];
 	if (!p2) {
 		p2 = p1[n] = kmalloc_array(64, sizeof(u16), GFP_KERNEL);
-		if (!p2) {
-			kfree(p1);
-			p->uni_pgdir[n] = NULL;
-			return -ENOMEM;
-		}
+		if (!p2) return -ENOMEM;
 		memset(p2, 0xff, 64*sizeof(u16)); /* No glyphs for the characters (yet) */
 	}

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