[PATCH] erofs-utils: lib: fix xattr crash in rebuild path when source has xattr

[Lucas Karpinski]

On 2026-03-02 8:03 a.m., lishixian wrote:
> When rebuilding from source EROFS images, erofs_read_xattrs_from_disk()
> is called for inodes that have xattr. At that point inode->sbi points to
> the source image's sbi, which is opened read-only and never gets
> erofs_xattr_init(), so sbi->xamgr is NULL. get_xattritem(sbi) then
> dereferences xamgr and crashes with SIGSEGV.
> 
> Fix by using the build target's xamgr when initializing src's sbi.
> 
> Reported-by: Yixiao Chen <489679970 at qq.com>
> Fixes: https://github.com/erofs/erofs-utils/issues/42
> Signed-off-by: lishixian <lishixian8 at huawei.com>
> Reviewed-by: Yifan Zhao <zhaoyifan28 at huawei.com>
> ---
>  lib/rebuild.c | 1 +
>  mkfs/main.c   | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/lib/rebuild.c b/lib/rebuild.c
> index f89a17c..f1e79c1 100644
> --- a/lib/rebuild.c
> +++ b/lib/rebuild.c
> @@ -437,6 +437,7 @@ int erofs_rebuild_load_tree(struct erofs_inode *root, struct erofs_sb_info *sbi,
>  		erofs_err("failed to read superblock of %s", fsid);
>  		return ret;
>  	}
> +	sbi->xamgr = g_sbi.xamgr;
>  
>  	inode.nid = sbi->root_nid;
>  	inode.sbi = sbi;
> diff --git a/mkfs/main.c b/mkfs/main.c
> index b84d1b4..cb0f0cc 100644
> --- a/mkfs/main.c
> +++ b/mkfs/main.c
> @@ -1011,6 +1011,7 @@ static void erofs_rebuild_cleanup(void)
>  
>  	list_for_each_entry_safe(src, n, &rebuild_src_list, list) {
>  		list_del(&src->list);
> +		src->xamgr = NULL; /* borrowed from g_sbi, do not free */
>  		erofs_put_super(src);
>  		erofs_dev_close(src);
>  		free(src);

I was similarly looking at this issue in my patchset so I can confirm it
fixes the seg fault.

Tested-by: Lucas Karpinski <lkarpinski at nvidia.com>