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    Subject[PATCH v2] x86/kexec: avoid double free_page() upon do_kexec_load() failure.
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    Date
    >From 91a78abed036e1662b11cb54ae6300864e17b709 Mon Sep 17 00:00:00 2001
    From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    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@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 | 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
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