From ac8fa186fc9293bb02eb28e56d5d1cca9ee89d6c Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Thu, 20 Oct 2022 17:18:58 +0200 Subject: [PATCH] UPSTREAM: fuse: fix readdir cache race [ Upstream commit 9fa248c65bdbf5af0a2f74dd38575acfc8dfd2bf ] There's a race in fuse's readdir cache that can result in an uninitilized page being read. The page lock is supposed to prevent this from happening but in the following case it doesn't: Two fuse_add_dirent_to_cache() start out and get the same parameters (size=0,offset=0). One of them wins the race to create and lock the page, after which it fills in data, sets rdc.size and unlocks the page. In the meantime the page gets evicted from the cache before the other instance gets to run. That one also creates the page, but finds the size to be mismatched, bails out and leaves the uninitialized page in the cache. Fix by marking a filled page uptodate and ignoring non-uptodate pages. Reported-by: Frank Sorenson Fixes: 5d7bc7e8680c ("fuse: allow using readdir cache") Cc: # v4.20 Change-Id: I1dea0531dd4d2cb0b89b8e1ee6796339fc2dc624 Signed-off-by: Miklos Szeredi Signed-off-by: Sasha Levin --- fs/fuse/readdir.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c index fb795bc4b286..f9d0be56d34a 100644 --- a/fs/fuse/readdir.c +++ b/fs/fuse/readdir.c @@ -79,8 +79,10 @@ static void fuse_add_dirent_to_cache(struct file *file, goto unlock; addr = kmap_atomic(page); - if (!offset) + if (!offset) { clear_page(addr); + SetPageUptodate(page); + } memcpy(addr + offset, dirent, reclen); kunmap_atomic(addr); fi->rdc.size = (index << PAGE_SHIFT) + offset + reclen; @@ -526,6 +528,12 @@ retry_locked: page = find_get_page_flags(file->f_mapping, index, FGP_ACCESSED | FGP_LOCK); + /* Page gone missing, then re-added to cache, but not initialized? */ + if (page && !PageUptodate(page)) { + unlock_page(page); + put_page(page); + page = NULL; + } spin_lock(&fi->rdc.lock); if (!page) { /*