In the Linux kernel, the following vulnerability has been resolved:
fuse: fix invalidate lock leak on open O_TRUNC DAX failure
fuse_open() takes filemap_invalidate_lock() for a DAX truncate
(dax_truncate = true) and releases it before the out_inode_unlock
label. But when fuse_dax_break_layouts() fails, the goto
out_inode_unlock skips the unlock and leaks the rwsem, so any later
fault or truncate on the file stalls on the stale lock.
fuse_dax_break_layouts() can fail with -ERESTARTSYS when a signal
interrupts the wait for busy DAX pages to drain:
open("file", O_RDWR | O_TRUNC)
└─ fuse_open()
├─ filemap_invalidate_lock() # dax_truncate
└─ fuse_dax_break_layouts()
└─ dax_break_layout()
└─ wait_page_idle() # TASK_INTERRUPTIBLE
└─ fuse_wait_dax_page() # unlock, schedule, re-lock
└─ signal → -ERESTARTSYS
goto out_inode_unlock # <- lock leaked
Fix this by moving filemap_invalidate_unlock() below the label so
that all error paths release the lock, and rename the label to
out_unlock as it now covers more than just the inode lock.