ext4: Avoid null pointer dereference when decoding EROFS w/o a journal

We need to check to make sure a journal is present before checking the
journal flags in ext4_decode_error().

Signed-off-by: Eric Sesterhenn <eric.sesterhenn@lsexperts.de>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 8f4f079e6b9a..fe3f376b7df2 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -344,7 +344,8 @@ static const char *ext4_decode_error(struct super_block *sb, int errno,
                 errstr = "Out of memory";
                 break;
         case -EROFS:
-                if (!sb || EXT4_SB(sb)->s_journal->j_flags & JBD2_ABORT)
+                if (!sb || (EXT4_SB(sb)->s_journal &&
+                            EXT4_SB(sb)->s_journal->j_flags & JBD2_ABORT))
                         errstr = "Journal has aborted";
                 else
                         errstr = "Readonly filesystem";