[PATCH] erofs: delimit inode_share cache key components

[ChengyuZhu6 <hudson@cyzhu.com>]

From: Chengyu Zhu <hudsonzhu@tencent.com>

The selected fingerprint xattr is treated as opaque and accepts any
positive length up to the filesystem block size.  Appending the domain ID
directly to such a value leaves no boundary between the two key components
if a different fingerprint length is used.

Change the key encoding as follows:

  fingerprint || domain_id  ->  domain_id || '\0' || fingerprint

Since a mount option string cannot contain NUL, this makes the in-memory
tuple unambiguous without constraining fingerprint contents or changing
the on-disk format.

Signed-off-by: Chengyu Zhu <hudsonzhu@tencent.com>
---
 fs/erofs/xattr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index df7ea019526d..17c640aca5f7 100644
--- a/fs/erofs/xattr.c
+++ b/fs/erofs/xattr.c
@@ -621,6 +621,7 @@ int erofs_xattr_fill_inode_fingerprint(struct erofs_inode_fingerprint *fp,
 	struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
 	struct erofs_xattr_prefix_item *prefix;
 	const char *infix;
+	size_t domainlen;
 	int valuelen, base_index;
 
 	if (!test_opt(&sbi->opt, INODE_SHARE))
@@ -633,17 +634,19 @@ int erofs_xattr_fill_inode_fingerprint(struct erofs_inode_fingerprint *fp,
 	valuelen = erofs_getxattr(inode, base_index, infix, NULL, 0);
 	if (valuelen <= 0 || valuelen > (1 << sbi->blkszbits))
 		return -EFSCORRUPTED;
-	fp->size = valuelen + (domain_id ? strlen(domain_id) : 0);
+	domain_id = domain_id ?: "";
+	domainlen = strlen(domain_id);
+	fp->size = domainlen + 1 + valuelen;
 	fp->opaque = kmalloc(fp->size, GFP_KERNEL);
 	if (!fp->opaque)
 		return -ENOMEM;
+	memcpy(fp->opaque, domain_id, domainlen + 1);
 	if (valuelen != erofs_getxattr(inode, base_index, infix,
-				       fp->opaque, valuelen)) {
+				       fp->opaque + domainlen + 1, valuelen)) {
 		kfree(fp->opaque);
 		fp->opaque = NULL;
 		return -EFSCORRUPTED;
 	}
-	memcpy(fp->opaque + valuelen, domain_id, fp->size - valuelen);
 	return 0;
 }
 #endif
-- 
2.51.0