UBIFS: fix an mmap and fsync race condition
There is a race condition in UBIFS:
Thread A (mmap) Thread B (fsync)
->__do_fault ->write_cache_pages
-> ubifs_vm_page_mkwrite
-> budget_space
-> lock_page
-> release/convert_page_budget
-> SetPagePrivate
-> TestSetPageDirty
-> unlock_page
-> lock_page
-> TestClearPageDirty
-> ubifs_writepage
-> do_writepage
-> release_budget
-> ClearPagePrivate
-> unlock_page
-> !(ret & VM_FAULT_LOCKED)
-> lock_page
-> set_page_dirty
-> ubifs_set_page_dirty
-> TestSetPageDirty (set page dirty without budgeting)
-> unlock_page
This leads to situation where we have a diry page but no budget allocated for
this page, so further write-back may fail with -ENOSPC.
In this fix we return from page_mkwrite without performing unlock_page. We
return VM_FAULT_LOCKED instead. After doing this, the race above will not
happen.
Signed-off-by: hujianyang <hujianyang@huawei.com>
Tested-by: Laurence Withers <lwithers@guralp.com>
Cc: stable@vger.kernel.org
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 4f34dba..f7d48a0 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -1525,8 +1525,7 @@
}
wait_for_stable_page(page);
- unlock_page(page);
- return 0;
+ return VM_FAULT_LOCKED;
out_unlock:
unlock_page(page);