linux-kernel - Re: [PATCH v3] ocfs2: fix oob in __ocfs2_find

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Message-ID: <rwy27v6h3su6i7osrb5aelexurlg7ggbzeedv7bghuwhe54uvl@nfwl3p5xugwh>
Date: Fri, 19 Dec 2025 15:59:10 +0800
From: Heming Zhao <heming.zhao@...e.com>
To: Edward Adam Davis <eadavis@...com>
Cc: eadavis@...org, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com, 
	linux-kernel@...r.kernel.org, mark@...heh.com, ocfs2-devel@...ts.linux.dev, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH v3] ocfs2: fix oob in __ocfs2_find_path

On Fri, Dec 19, 2025 at 03:43:32PM +0800, Edward Adam Davis wrote:
> syzbot constructed a corrupted image, which resulted in the l_count
> value of the root element being 0. Since the length of the l_recs
> array depends on l_count, reading its member e_blkno triggered the
> out-of-bounds access reported by syzbot in [1].

for: "which resulted in the l_count of the root element being 0"
This issue occurs not only in the root extent but also in every node of the
b-tree. It's better to use a more general description, such as:
which resulted in el->l_count from the b-tree extent block being 0.

- Heming
> 
> The loop terminates when l_count is 0, similar to when next_free is 0.
> 
> [1]
> UBSAN: array-index-out-of-bounds in fs/ocfs2/alloc.c:1838:11
> index 0 is out of range for type 'struct ocfs2_extent_rec[] __counted_by(l_count)' (aka 'struct ocfs2_extent_rec[]')
> Call Trace:
>  __ocfs2_find_path+0x606/0xa40 fs/ocfs2/alloc.c:1838
>  ocfs2_find_leaf+0xab/0x1c0 fs/ocfs2/alloc.c:1946
>  ocfs2_get_clusters_nocache+0x172/0xc60 fs/ocfs2/extent_map.c:418
>  ocfs2_get_clusters+0x505/0xa70 fs/ocfs2/extent_map.c:631
>  ocfs2_extent_map_get_blocks+0x202/0x6a0 fs/ocfs2/extent_map.c:678
>  ocfs2_read_virt_blocks+0x286/0x930 fs/ocfs2/extent_map.c:1001
>  ocfs2_read_dir_block fs/ocfs2/dir.c:521 [inline]
>  ocfs2_find_entry_el fs/ocfs2/dir.c:728 [inline]
>  ocfs2_find_entry+0x3e4/0x2090 fs/ocfs2/dir.c:1120
>  ocfs2_find_files_on_disk+0xdf/0x310 fs/ocfs2/dir.c:2023
>  ocfs2_lookup_ino_from_name+0x52/0x100 fs/ocfs2/dir.c:2045
>  _ocfs2_get_system_file_inode fs/ocfs2/sysfile.c:136 [inline]
>  ocfs2_get_system_file_inode+0x326/0x770 fs/ocfs2/sysfile.c:112
>  ocfs2_init_global_system_inodes+0x319/0x660 fs/ocfs2/super.c:461
>  ocfs2_initialize_super fs/ocfs2/super.c:2196 [inline]
>  ocfs2_fill_super+0x4432/0x65b0 fs/ocfs2/super.c:993
>  get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
>  vfs_get_tree+0x92/0x2a0 fs/super.c:1751
>  fc_mount fs/namespace.c:1199 [inline]
> 
> Reported-by: syzbot+151afab124dfbc5f15e6@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=151afab124dfbc5f15e6
> Signed-off-by: Edward Adam Davis <eadavis@...com>
> ---
> v2 -> v3: remove le16 and Fix tag and update comments
> v1 -> v2: check l_count and update comments
> 
>  fs/ocfs2/alloc.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index 58bf58b68955..b7db177d17d6 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -1812,14 +1812,15 @@ static int __ocfs2_find_path(struct ocfs2_caching_info *ci,
>  			ret = -EROFS;
>  			goto out;
>  		}
> -		if (le16_to_cpu(el->l_next_free_rec) == 0) {
> +		if (!el->l_next_free_rec || !el->l_count) {
>  			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
> -				    "Owner %llu has empty extent list at depth %u\n",
> +				    "Owner %llu has empty extent list at depth %u\n"
> +				    "(next free=%u count=%u)\n",
>  				    (unsigned long long)ocfs2_metadata_cache_owner(ci),
> -				    le16_to_cpu(el->l_tree_depth));
> +				    le16_to_cpu(el->l_tree_depth),
> +				    le16_to_cpu(el->l_next_free_rec), le16_to_cpu(el->l_count));
>  			ret = -EROFS;
>  			goto out;
> -
>  		}
>  
>  		for(i = 0; i < le16_to_cpu(el->l_next_free_rec) - 1; i++) {
> -- 
> 2.43.0
>