fs/ntfs3: prevent infinite loops caused by the next valid being the same

In the Linux kernel, the following vulnerability has been resolved:

fs/ntfs3: prevent infinite loops caused by the next valid being the same

When processing valid within the range [valid : pos), if valid cannot

be retrieved correctly, for example, if the retrieved valid value is

always the same, this can trigger a potential infinite loop, similar

to the hung problem reported by syzbot [1].

Adding a check for the valid value within the loop body, and terminating

the loop and returning -EINVAL if the value is the same as the current

value, can prevent this.

[1]

INFO: task syz.4.21:6056 blocked for more than 143 seconds.

Call Trace:

rwbase_write_lock+0x14f/0x750 kernel/locking/rwbase_rt.c:244

inode_lock include/linux/fs.h:1027 [inline]

ntfs_file_write_iter+0xe6/0x870 fs/ntfs3/file.c:1284