[PATCH v2] x86/kexec: avoid double free_page() upon do_kexec_load() failure.

[Tetsuo Handa]

Baoquan He wrote:
> On 05/01/18 at 07:10pm, Tetsuo Handa wrote:
> > From d54b2acf63191eba3d5052bf34fe6d26e3580ac2 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Date: Tue, 1 May 2018 15:36:52 +0900
> > Subject: [PATCH] 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 explicitly setting NULL after free_page().
> 
> Setting them NULL after free_page() is a good idea.

That's what the V1 patch did.

>                                                     Maybe can remove the
> double calling of free_transition_pgtable() too in init_transition_pgtable()
> because the returned value will trigger the later calling.

That's what the V2 patch did. You can apply V1 or V2 or V1 + V2.

>From 91a78abed036e1662b11cb54ae6300864e17b709 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 4 May 2018 08:26:41 +0900
Subject: [PATCH v2] 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().

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

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+d96f60296ef613fe1d69@xxxxxxxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
---
 arch/x86/kernel/machine_kexec_32.c | 1 -
 arch/x86/kernel/machine_kexec_64.c | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_32.c b/arch/x86/kernel/machine_kexec_32.c
index 60cdec6..170fbf8 100644
--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -79,7 +79,6 @@ 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..ffe0174 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -91,7 +91,6 @@ 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