1. 01 Nov, 2023 1 commit
    • Brian Foster's avatar
      ext4: fix racy may inline data check in dio write · ce56d213
      Brian Foster authored
      syzbot reports that the following warning from ext4_iomap_begin()
      triggers as of the commit referenced below:
      
              if (WARN_ON_ONCE(ext4_has_inline_data(inode)))
                      return -ERANGE;
      
      This occurs during a dio write, which is never expected to encounter
      an inode with inline data. To enforce this behavior,
      ext4_dio_write_iter() checks the current inline state of the inode
      and clears the MAY_INLINE_DATA state flag to either fall back to
      buffered writes, or enforce that any other writers in progress on
      the inode are not allowed to create inline data.
      
      The problem is that the check for existing inline data and the state
      flag can span a lock cycle. For example, if the ilock is originally
      locked shared and subsequently upgraded to exclusive, another writer
      may have reacquired the lock and created inline data before the dio
      write task acquires the lock and proceeds.
      
      The commit referenced below loosens the lock requirements to allow
      some forms of unaligned dio writes to occur under shared lock, but
      AFAICT the inline data check was technically already racy for any
      dio write that would have involved a lock cycle. Regardless, lift
      clearing of the state bit to the same lock critical section that
      checks for preexisting inline data on the inode to close the race.
      
      Cc: stable@kernel.org
      Reported-by: syzbot+307da6ca5cb0d01d581a@syzkaller.appspotmail.com
      Fixes: 310ee090 ("ext4: allow concurrent unaligned dio overwrites")
      Signed-off-by: default avatarBrian Foster <bfoster@redhat.com>
      Link: https://lore.kernel.org/r/20231002185020.531537-1-bfoster@redhat.comSigned-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
      ce56d213
  2. 06 Oct, 2023 39 commits