From: Miklos Szeredi mszeredi@redhat.com
[ 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 fsorenso@redhat.com Fixes: 5d7bc7e8680c ("fuse: allow using readdir cache") Cc: stable@vger.kernel.org # v4.20 Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 bc267832310c..d5294e663df5 100644 --- a/fs/fuse/readdir.c +++ b/fs/fuse/readdir.c @@ -77,8 +77,10 @@ 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; @@ -516,6 +518,12 @@ static int fuse_readdir_cached(struct file *file, struct dir_context *ctx)
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) { /*