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    SubjectRe: kernel BUG at include/linux/mm.h:LINE!
    From
    Date
    From d54b2acf63191eba3d5052bf34fe6d26e3580ac2 Mon Sep 17 00:00:00 2001
    From: Tetsuo Handa <penguin-kernel@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().

    [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 | 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
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