f2fs: fix to avoid NULL pointer dereference in f2fs_issue_flush()

With below two cases, it will cause NULL pointer dereference when
accessing SM_I(sbi)->fcc_info in f2fs_issue_flush().

a) If kthread_run() fails in f2fs_create_flush_cmd_control(), it will
release SM_I(sbi)->fcc_info,

- mount -o noflush_merge /dev/vda /mnt/f2fs
- mount -o remount,flush_merge /dev/vda /mnt/f2fs  -- kthread_run() fails
- dd if=/dev/zero of=/mnt/f2fs/file bs=4k count=1 conv=fsync

b) we will never allocate memory for SM_I(sbi)->fcc_info w/ below
testcase,

- mount -o ro /dev/vda /mnt/f2fs
- mount -o rw,remount /dev/vda /mnt/f2fs
- dd if=/dev/zero of=/mnt/f2fs/file bs=4k count=1 conv=fsync

In order to fix this issue, let change as below:
- fix error path handling in f2fs_create_flush_cmd_control().
- allocate SM_I(sbi)->fcc_info even if readonly is on.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 25ddea478fc1a8a628bf4e59d10584836a96052e..c3f8c8208eecaa271a2fc1516488a2b8ec1a9527 100644 (file)
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -663,8 +663,7 @@ init_thread:
        if (IS_ERR(fcc->f2fs_issue_flush)) {
                int err = PTR_ERR(fcc->f2fs_issue_flush);
 
-               kfree(fcc);
-               SM_I(sbi)->fcc_info = NULL;
+               fcc->f2fs_issue_flush = NULL;
                return err;
        }
 
@@ -5138,11 +5137,9 @@ int f2fs_build_segment_manager(struct f2fs_sb_info *sbi)
 
        init_f2fs_rwsem(&sm_info->curseg_lock);
 
-       if (!f2fs_readonly(sbi->sb)) {
-               err = f2fs_create_flush_cmd_control(sbi);
-               if (err)
-                       return err;
-       }
+       err = f2fs_create_flush_cmd_control(sbi);
+       if (err)
+               return err;
 
        err = create_discard_cmd_control(sbi);
        if (err)