fuse: fix invalidate lock leak on setattr writeback failure

Overview

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

fuse: fix invalidate lock leak on setattr writeback failure

fuse_do_setattr() takes filemap_invalidate_lock() for a DAX truncate (fault_blocked = true) and releases it at the out:/error: labels. But when a writeback flush is also needed, a write_inode_now() failure returns directly and leaks the lock, so any later fault or truncate on the file stalls on the stale rwsem.

For example, truncate(2) on a setuid file reaches fuse_do_setattr() with both ATTR_SIZE and ATTR_MODE set:

truncate(2) └─ do_truncate() ├─ dentry_needs_remove_privs() # S_ISUID └─ notify_change() # KILL_SUID -> ATTR_MODE └─ fuse_setattr() # no killpriv: │ # ia_valid |= ATTR_MODE └─ fuse_do_setattr() ├─ filemap_invalidate_lock() # IS_DAX && is_truncate └─ write_inode_now() # is_wb && ATTR_MODE └─ if (err) # e.g. daemon -> -EIO return err # <- lock leaked

Fix this by adding an unlock label that releases the lock before returning the error, and use it for the fuse_dax_break_layouts() failure path as well.

Affected

• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < 8f14906ce9103ab8f2f1ebda45935a0d61b9d763
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < 03cfeeb135428fa83f0791d3f8f94d9298cae695
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < 92588d187ba4697a322e7aefe5d9e538a87d1cd2
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < ea9fea370b8de4ffd72e0ef89550415c15637787
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < 1758730d9eaa3c06cf415c3446d9f6eed9ed3eed
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < dd278d954c0e96a9cbd3cc491e07b8267d25f8d5
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < e8457ebfd77a46e8d1210e8888ea914ad064558e
• Linux >= 6ae330cad6ef22ab8347ea9e0707dc56a7c7363f < 9afeca0d569c9fc89d758fe7a9339d1e8afb1546
• Linux 5.10

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.