2018-01-15 11:26:15 +00:00
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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2018-01-06 14:13:39 +00:00
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Sun, 31 Dec 2017 11:24:34 +0100
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2018-01-15 11:26:15 +00:00
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Subject: [PATCH] x86/ldt: Plug memory leak in error path
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2018-01-06 14:13:39 +00:00
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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CVE-2017-5754
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The error path in write_ldt() tries to free 'old_ldt' instead of the newly
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allocated 'new_ldt', resulting in a memory leak. It also misses to clean up a
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half populated LDT pagetable, which is not a leak as it gets cleaned up
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when the process exits.
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Free both the potentially half populated LDT pagetable and the newly
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allocated LDT struct. This can be done unconditionally because once an LDT
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is mapped subsequent maps will succeed, because the PTE page is already
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populated and the two LDTs fit into that single page.
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Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Cc: Andy Lutomirski <luto@kernel.org>
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Cc: Borislav Petkov <bp@alien8.de>
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Cc: Dave Hansen <dave.hansen@linux.intel.com>
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Cc: Dominik Brodowski <linux@dominikbrodowski.net>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Linus Torvalds <torvalds@linuxfoundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Fixes: f55f0501cbf6 ("x86/pti: Put the LDT in its own PGD if PTI is on")
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Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1712311121340.1899@nanos
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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(cherry picked from commit a62d69857aab4caa43049e72fe0ed5c4a60518dd)
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Signed-off-by: Andy Whitcroft <apw@canonical.com>
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Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
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(cherry picked from commit 03d02494f6253d0bdca7254d85e50786448c14f9)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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arch/x86/kernel/ldt.c | 8 +++++++-
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1 file changed, 7 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
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index 2260eb6e2de7..9a35b7e541bc 100644
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--- a/arch/x86/kernel/ldt.c
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+++ b/arch/x86/kernel/ldt.c
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@@ -420,7 +420,13 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
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*/
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error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
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if (error) {
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- free_ldt_struct(old_ldt);
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+ /*
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+ * This only can fail for the first LDT setup. If an LDT is
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+ * already installed then the PTE page is already
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+ * populated. Mop up a half populated page table.
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+ */
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+ free_ldt_pgtables(mm);
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+ free_ldt_struct(new_ldt);
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goto out_unlock;
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}
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--
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2.14.2
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