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

commit 78f1ddbb498283c2445c11b0dfa666424c301803 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index db2642a..baacaf8 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -254,7 +254,8 @@ 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";