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mm: fix NULL pointer dereference in wp_page_reuse()

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The vmf->page can be NULL when the wp_page_reuse() is invoked by
wp_pfn_shared(), it will cause the following panic:

  BUG: kernel NULL pointer dereference, address: 000000000000008
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEMPT SMP PTI
  CPU: 18 PID: 923 Comm: Xorg Not tainted 5.19.0-rc8.bm.1-amd64 #263
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g14
  RIP: 0010:_compound_head+0x0/0x40
  [...]
  Call Trace:
    wp_page_reuse+0x1c/0xa0
    do_wp_page+0x1a5/0x3f0
    __handle_mm_fault+0x8cf/0xd20
    handle_mm_fault+0xd5/0x2a0
    do_user_addr_fault+0x1d0/0x680
    exc_page_fault+0x78/0x170
    asm_exc_page_fault+0x22/0x30

To fix it, this patch performs a NULL pointer check before dereferencing
the vmf->page.

Fixes: 6c287605fd ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Qi Zheng 2022-07-26 14:24:36 +08:00 committed by Linus Torvalds
parent e0dccc3b76
commit cdb281e638
1 changed files with 1 additions and 1 deletions
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2
mm/memory.c
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@ -3043,7 +3043,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
pte_t entry;
VM_BUG_ON(!(vmf->flags & FAULT_FLAG_WRITE));
VM_BUG_ON(PageAnon(page) && !PageAnonExclusive(page));
VM_BUG_ON(page && PageAnon(page) && !PageAnonExclusive(page));
/*
* Clear the pages cpupid information as the existing