On 05/01/18 at 07:10pm, Tetsuo Handa wrote: > From d54b2acf63191eba3d5052bf34fe6d26e3580ac2 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> > 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. Maybe can remove the double calling of free_transition_pgtable() too in init_transition_pgtable() because the returned value will trigger the later calling. > > [1] > https://syzkaller.appspot.com/bug?id=91e52396168cf2bdd572fe1e1bc0bc645c1c6b40 > > Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> > Reported-by: syzbot <syzbot+d96f60296ef613fe1...@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.hu...@intel.com> > Cc: H. Peter Anvin <h...@zytor.com> > Cc: Ingo Molnar <mi...@elte.hu> > --- > arch/x86/kernel/machine_kexec_32.c | 5 +++++ > arch/x86/kernel/machine_kexec_64.c | 4 ++++ > 2 files changed, 9 insertions(+) > > diff --git a/arch/x86/kernel/machine_kexec_32.c > b/arch/x86/kernel/machine_kexec_32.c > index 60cdec6..ceccfe4 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) > diff --git a/arch/x86/kernel/machine_kexec_64.c > b/arch/x86/kernel/machine_kexec_64.c > index a5e55d8..76aaee9 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) > -- > 1.8.3.1 >
