From 1b9b922a3a601b0c99a095ffafed61fcf6ebe0b7 Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Tue, 15 Dec 2015 07:15:32 -0800 Subject: [PATCH] Btrfs: check for empty bitmap list in setup_cluster_bitmaps Dave Jones found a warning from kasan in setup_cluster_bitmaps() ================================================================== BUG: KASAN: stack-out-of-bounds in setup_cluster_bitmap+0xc4/0x5a0 at addr ffff88039bef6828 Read of size 8 by task nfsd/1009 page:ffffea000e6fbd80 count:0 mapcount:0 mapping: (null) index:0x0 flags: 0x8000000000000000() page dumped because: kasan: bad access detected CPU: 1 PID: 1009 Comm: nfsd Tainted: G W 4.4.0-rc3-backup-debug+ #1 ffff880065647b50 000000006bb712c2 ffff88039bef6640 ffffffffa680a43e 0000004559c00000 ffff88039bef66c8 ffffffffa62638d1 ffffffffa61121c0 ffff8803a5769de8 0000000000000296 ffff8803a5769df0 0000000000046280 Call Trace: [] dump_stack+0x4b/0x6d [] kasan_report_error+0x501/0x520 [] ? debug_show_all_locks+0x1e0/0x1e0 [] kasan_report+0x58/0x60 [] ? rb_last+0x10/0x40 [] ? setup_cluster_bitmap+0xc4/0x5a0 [] __asan_load8+0x5d/0x70 [] setup_cluster_bitmap+0xc4/0x5a0 [] ? setup_cluster_no_bitmap+0x6a/0x400 [] btrfs_find_space_cluster+0x4b6/0x640 [] ? btrfs_alloc_from_cluster+0x4e0/0x4e0 [] ? btrfs_return_cluster_to_free_space+0x9e/0xb0 [] ? _raw_spin_unlock+0x27/0x40 [] find_free_extent+0xba1/0x1520 Andrey noticed this was because we were doing list_first_entry on a list that might be empty. Rework the tests a bit so we don't do that. Signed-off-by: Chris Mason Reprorted-by: Andrey Ryabinin Reported-by: Dave Jones --- fs/btrfs/free-space-cache.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c index 0948d34cb84a..e6fc7d9e65b1 100644 --- a/fs/btrfs/free-space-cache.c +++ b/fs/btrfs/free-space-cache.c @@ -2972,7 +2972,7 @@ setup_cluster_bitmap(struct btrfs_block_group_cache *block_group, u64 cont1_bytes, u64 min_bytes) { struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl; - struct btrfs_free_space *entry; + struct btrfs_free_space *entry = NULL; int ret = -ENOSPC; u64 bitmap_offset = offset_to_bitmap(ctl, offset); @@ -2983,8 +2983,10 @@ setup_cluster_bitmap(struct btrfs_block_group_cache *block_group, * The bitmap that covers offset won't be in the list unless offset * is just its start offset. */ - entry = list_first_entry(bitmaps, struct btrfs_free_space, list); - if (entry->offset != bitmap_offset) { + if (!list_empty(bitmaps)) + entry = list_first_entry(bitmaps, struct btrfs_free_space, list); + + if (!entry || entry->offset != bitmap_offset) { entry = tree_search_offset(ctl, bitmap_offset, 1, 0); if (entry && list_empty(&entry->list)) list_add(&entry->list, bitmaps); -- 2.34.1