1. 26 Jul, 2022 1 commit
    • Qi Zheng's avatar
      mm: fix NULL pointer dereference in wp_page_reuse() · cdb281e6
      Qi Zheng authored
      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: 6c287605 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
      Signed-off-by: default avatarQi Zheng <zhengqi.arch@bytedance.com>
      Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      cdb281e6
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