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