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

[lishixian]

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);
-- 
2.47.3