From 691a7c6f28ac90cccd0dbcf81348ea90b211bdd0 Mon Sep 17 00:00:00 2001 From: hujianyang Date: Wed, 30 Apr 2014 14:06:06 +0800 Subject: [PATCH] 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 Tested-by: Laurence Withers Cc: stable@vger.kernel.org Signed-off-by: Artem Bityutskiy --- fs/ubifs/file.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c index 4f34dbae823d..f7d48a08f443 100644 --- a/fs/ubifs/file.c +++ b/fs/ubifs/file.c @@ -1525,8 +1525,7 @@ static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma, } wait_for_stable_page(page); - unlock_page(page); - return 0; + return VM_FAULT_LOCKED; out_unlock: unlock_page(page); -- 2.39.5