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: [<ffffffffa680a43e>] dump_stack+0x4b/0x6d [<ffffffffa62638d1>] kasan_report_error+0x501/0x520 [<ffffffffa61121c0>] ? debug_show_all_locks+0x1e0/0x1e0 [<ffffffffa6263948>] kasan_report+0x58/0x60 [<ffffffffa6814b00>] ? rb_last+0x10/0x40 [<ffffffffa66f8af4>] ? setup_cluster_bitmap+0xc4/0x5a0 [<ffffffffa6262ead>] __asan_load8+0x5d/0x70 [<ffffffffa66f8af4>] setup_cluster_bitmap+0xc4/0x5a0 [<ffffffffa66f675a>] ? setup_cluster_no_bitmap+0x6a/0x400 [<ffffffffa66fcd16>] btrfs_find_space_cluster+0x4b6/0x640 [<ffffffffa66fc860>] ? btrfs_alloc_from_cluster+0x4e0/0x4e0 [<ffffffffa66fc36e>] ? btrfs_return_cluster_to_free_space+0x9e/0xb0 [<ffffffffa702dc37>] ? _raw_spin_unlock+0x27/0x40 [<ffffffffa666a1a1>] 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 <clm@fb.com> Reprorted-by: Andrey Ryabinin <ryabinin.a.a@gmail.com> Reported-by: Dave Jones <dsj@fb.com>
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@ -2972,7 +2972,7 @@ setup_cluster_bitmap(struct btrfs_block_group_cache *block_group,
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u64 cont1_bytes, u64 min_bytes)
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{
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struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
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struct btrfs_free_space *entry;
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struct btrfs_free_space *entry = NULL;
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int ret = -ENOSPC;
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u64 bitmap_offset = offset_to_bitmap(ctl, offset);
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@ -2983,8 +2983,10 @@ setup_cluster_bitmap(struct btrfs_block_group_cache *block_group,
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* The bitmap that covers offset won't be in the list unless offset
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* is just its start offset.
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*/
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entry = list_first_entry(bitmaps, struct btrfs_free_space, list);
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if (entry->offset != bitmap_offset) {
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if (!list_empty(bitmaps))
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entry = list_first_entry(bitmaps, struct btrfs_free_space, list);
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if (!entry || entry->offset != bitmap_offset) {
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entry = tree_search_offset(ctl, bitmap_offset, 1, 0);
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if (entry && list_empty(&entry->list))
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list_add(&entry->list, bitmaps);
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