From cc8c67cadc2749c74c4ebaee16e8d8935f0cfda4 Mon Sep 17 00:00:00 2001 From: David Sterba Date: Fri, 12 May 2017 01:03:52 +0200 Subject: btrfs: use correct types for page indices in btrfs_page_exists_in_range commit cc2b702c52094b637a351d7491ac5200331d0445 upstream. Variables start_idx and end_idx are supposed to hold a page index derived from the file offsets. The int type is not the right one though, offsets larger than 1 << 44 will get silently trimmed off the high bits. (1 << 44 is 16TiB) What can go wrong, if start is below the boundary and end gets trimmed: - if there's a page after start, we'll find it (radix_tree_gang_lookup_slot) - the final check "if (page->index <= end_idx)" will unexpectedly fail The function will return false, ie. "there's no page in the range", although there is at least one. btrfs_page_exists_in_range is used to prevent races in: * in hole punching, where we make sure there are not pages in the truncated range, otherwise we'll wait for them to finish and redo truncation, but we're going to replace the pages with holes anyway so the only problem is the intermediate state * lock_extent_direct: we want to make sure there are no pages before we lock and start DIO, to prevent stale data reads For practical occurence of the bug, there are several constaints. The file must be quite large, the affected range must cross the 16TiB boundary and the internal state of the file pages and pending operations must match. Also, we must not have started any ordered data in the range, otherwise we don't even reach the buggy function check. DIO locking tries hard in several places to avoid deadlocks with buffered IO and avoids waiting for ranges. The worst consequence seems to be stale data read. CC: Liu Bo Fixes: fc4adbff823f7 ("btrfs: Drop EXTENT_UPTODATE check in hole punching and direct locking") Reviewed-by: Liu Bo Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs/btrfs/inode.c') diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 3cff6523f27d..863fa0f1972b 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -7318,8 +7318,8 @@ bool btrfs_page_exists_in_range(struct inode *inode, loff_t start, loff_t end) int found = false; void **pagep = NULL; struct page *page = NULL; - int start_idx; - int end_idx; + unsigned long start_idx; + unsigned long end_idx; start_idx = start >> PAGE_CACHE_SHIFT; -- cgit v1.2.3