libext2fs: fix crash when ext2fs_mmp_stop() is called before MMP is initialized

The fatal_error() function in e2fsck can call ext2fs_mmp_stop() on a
file system where MMP hasn't yet been initialized.  When that happens,
instead of crashing, have ext2fs_mmp_stop() return success, since mmp
doesn't need to be stopped if it hasn't even been initialized yet.

Addresses-Debian-Bug: #696609
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c
index c21ae27..023dccf 100644 (file)
--- a/lib/ext2fs/mmp.c
+++ b/lib/ext2fs/mmp.c
@@ -403,7 +403,8 @@ errcode_t ext2fs_mmp_stop(ext2_filsys fs)
        errcode_t retval = 0;
 
        if (!ext2fs_has_feature_mmp(fs->super) ||
-           !(fs->flags & EXT2_FLAG_RW) || (fs->flags & EXT2_FLAG_SKIP_MMP))
+           !(fs->flags & EXT2_FLAG_RW) || (fs->flags & EXT2_FLAG_SKIP_MMP) ||
+           (fs->mmp_buf == NULL) || (fs->mmp_cmp == NULL))
                goto mmp_error;
 
        retval = ext2fs_mmp_read(fs, fs->super->s_mmp_block, fs->mmp_buf);