dont-try-to-set-hash-signedness-flag-if-fs-is-ro

   1 ext4: don't try to modify s_flags if the the file system is read-only
   2
   3 If an ext4 file system is created by some tool other than mke2fs
   4 (perhaps by someone who has a pathalogical fear of the GPL) that
   5 doesn't set one or the other of the EXT2_FLAGS_{UN}SIGNED_HASH flags,
   6 and that file system is then mounted read-only, don't try to modify
   7 the s_flags field.  Otherwise, if dm_verity is in use, the superblock
   8 will change, causing an dm_verity failure.
   9
  10 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  11 Cc: stable@vger.kernel.org
  12 ---
  13  fs/ext4/super.c | 20 +++++++++++++-------
  14  1 file changed, 13 insertions(+), 7 deletions(-)
  15
  16 diff --git a/fs/ext4/super.c b/fs/ext4/super.c
  17 index 0491c81..f5c13b8 100644
  18 --- a/fs/ext4/super.c
  19 +++ b/fs/ext4/super.c
  20 @@ -3695,16 +3695,22 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
  21         for (i = 0; i < 4; i++)
  22                 sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
  23         sbi->s_def_hash_version = es->s_def_hash_version;
  24 -       i = le32_to_cpu(es->s_flags);
  25 -       if (i & EXT2_FLAGS_UNSIGNED_HASH)
  26 -               sbi->s_hash_unsigned = 3;
  27 -       else if ((i & EXT2_FLAGS_SIGNED_HASH) == 0) {
  28 +       if (EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_DIR_INDEX)) {
  29 +               i = le32_to_cpu(es->s_flags);
  30 +               if (i & EXT2_FLAGS_UNSIGNED_HASH)
  31 +                       sbi->s_hash_unsigned = 3;
  32 +               else if ((i & EXT2_FLAGS_SIGNED_HASH) == 0) {
  33  #ifdef __CHAR_UNSIGNED__
  34 -               es->s_flags |= cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH);
  35 -               sbi->s_hash_unsigned = 3;
  36 +                       if (!(sb->s_flags & MS_RDONLY))
  37 +                               es->s_flags |=
  38 +                                       cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH);
  39 +                       sbi->s_hash_unsigned = 3;
  40  #else
  41 -               es->s_flags |= cpu_to_le32(EXT2_FLAGS_SIGNED_HASH);
  42 +                       if (!(sb->s_flags & MS_RDONLY))
  43 +                               es->s_flags |=
  44 +                                       cpu_to_le32(EXT2_FLAGS_SIGNED_HASH);
  45  #endif
  46 +               }
  47         }
  48
  49         /* Handle clustersize */