[PATCH v3] x86/kexec: avoid double free_page() upon do_kexec_load() failure.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

>From ff82bedd3e12f0d3353282054ae48c3bd8c72012 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Wed, 9 May 2018 12:12:39 +0900
Subject: [PATCH v3] x86/kexec: avoid double free_page() upon do_kexec_load() failure.

syzbot is reporting crashes after memory allocation failure inside
do_kexec_load() [1]. This is because free_transition_pgtable() is called
by both init_transition_pgtable() and machine_kexec_cleanup() when memory
allocation failed inside init_transition_pgtable().

Regarding 32bit code, machine_kexec_free_page_tables() is called by both
machine_kexec_alloc_page_tables() and machine_kexec_cleanup() when memory
allocation failed inside machine_kexec_alloc_page_tables().

Fix this by leaving the error handling to machine_kexec_cleanup()
(and optionally setting NULL after free_page()).

[1] https://syzkaller.appspot.com/bug?id=91e52396168cf2bdd572fe1e1bc0bc645c1c6b40

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+d96f60296ef613fe1d69@syzkaller.appspotmail.com>
Fixes: f5deb79679af6eb4 ("x86: kexec: Use one page table in x86_64 machine_kexec")
Fixes: 92be3d6bdf2cb349 ("kexec/i386: allocate page table pages dynamically")
Cc: Huang Ying <ying.huang@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/machine_kexec_32.c | 6 +++++-
 arch/x86/kernel/machine_kexec_64.c | 5 ++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_32.c b/arch/x86/kernel/machine_kexec_32.c
index 60cdec6..d1ab07e 100644
--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -57,12 +57,17 @@ static void load_segments(void)
 static void machine_kexec_free_page_tables(struct kimage *image)
 {
 	free_page((unsigned long)image->arch.pgd);
+	image->arch.pgd = NULL;
 #ifdef CONFIG_X86_PAE
 	free_page((unsigned long)image->arch.pmd0);
+	image->arch.pmd0 = NULL;
 	free_page((unsigned long)image->arch.pmd1);
+	image->arch.pmd1 = NULL;
 #endif
 	free_page((unsigned long)image->arch.pte0);
+	image->arch.pte0 = NULL;
 	free_page((unsigned long)image->arch.pte1);
+	image->arch.pte1 = NULL;
 }
 
 static int machine_kexec_alloc_page_tables(struct kimage *image)
@@ -79,7 +84,6 @@ static int machine_kexec_alloc_page_tables(struct kimage *image)
 	    !image->arch.pmd0 || !image->arch.pmd1 ||
 #endif
 	    !image->arch.pte0 || !image->arch.pte1) {
-		machine_kexec_free_page_tables(image);
 		return -ENOMEM;
 	}
 	return 0;
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index a5e55d8..6010449 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -39,9 +39,13 @@
 static void free_transition_pgtable(struct kimage *image)
 {
 	free_page((unsigned long)image->arch.p4d);
+	image->arch.p4d = NULL;
 	free_page((unsigned long)image->arch.pud);
+	image->arch.pud = NULL;
 	free_page((unsigned long)image->arch.pmd);
+	image->arch.pmd = NULL;
 	free_page((unsigned long)image->arch.pte);
+	image->arch.pte = NULL;
 }
 
 static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
@@ -91,7 +95,6 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
 	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC_NOENC));
 	return 0;
 err:
-	free_transition_pgtable(image);
 	return result;
 }
 
-- 
1.8.3.1