1. 11 Jul, 2024 1 commit
    • Baokun Li's avatar
      ext4: check dot and dotdot of dx_root before making dir indexed · 50ea741d
      Baokun Li authored
      Syzbot reports a issue as follows:
      ============================================
      BUG: unable to handle page fault for address: ffffed11022e24fe
      PGD 23ffee067 P4D 23ffee067 PUD 0
      Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
      CPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e68 #0
      Call Trace:
       <TASK>
       make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341
       ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451
       ext4_rename fs/ext4/namei.c:3936 [inline]
       ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214
      [...]
      ============================================
      
      The immediate cause of this problem is that there is only one valid dentry
      for the block to be split during do_split, so split==0 results in out of
      bounds accesses to the map triggering the issue.
      
          do_split
            unsigned split
            dx_make_map
             count = 1
            split = count/2 = 0;
            continued = hash2 == map[split - 1].hash;
             ---> map[4294967295]
      
      The maximum length of a filename is 255 and the minimum block size is 1024,
      so it is always guaranteed that the number of entries is greater than or
      equal to 2 when do_split() is called.
      
      But syzbot's crafted image has no dot and dotdot in dir, and the dentry
      distribution in dirblock is as follows:
      
        bus     dentry1          hole           dentry2           free
      |xx--|xx-------------|...............|xx-------------|...............|
      0   12 (8+248)=256  268     256     524 (8+256)=264 788     236     1024
      
      So when renaming dentry1 increases its name_len length by 1, neither hole
      nor free is sufficient to hold the new dentry, and make_indexed_dir() is
      called.
      
      In make_indexed_dir() it is assumed that the first two entries of the
      dirblock must be dot and dotdot, so bus and dentry1 are left in dx_root
      because they are treated as dot and dotdot, and only dentry2 is moved
      to the new leaf block. That's why count is equal to 1.
      
      Therefore add the ext4_check_dx_root() helper function to add more sanity
      checks to dot and dotdot before starting the conversion to avoid the above
      issue.
      
      Reported-by: syzbot+ae688d469e36fb5138d0@syzkaller.appspotmail.com
      Closes: https://syzkaller.appspot.com/bug?extid=ae688d469e36fb5138d0
      Fixes: ac27a0ec ("[PATCH] ext4: initial copy of files from ext3")
      Cc: stable@kernel.org
      Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
      Reviewed-by: default avatarJan Kara <jack@suse.cz>
      Link: https://patch.msgid.link/20240702132349.2600605-2-libaokun@huaweicloud.comSigned-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
      50ea741d
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