[PATCH 6.18.y] ksmbd: look up stream size by exact xattr name

[Sasha Levin <sashal@kernel.org>]

From: Gael Blivet <gael.blivet@gmail.com>

[ Upstream commit 10ea20d6584ecdaf2f7505855412a856a88d8934 ]

get_file_stream_info() walks the xattr list from a single
ksmbd_vfs_listxattr() and sizes each stream it finds with
ksmbd_vfs_casexattr_len(), which matches with strncasecmp(). Linux
xattr names are case-sensitive, so two streams differing only in case
report each other's size.

The loop already holds the exact name, so query it directly with
ksmbd_vfs_xattr_len(), which is what casexattr_len() calls once its
search succeeds. Make it non-static and declare it in vfs.h, and drop
the comment above it, which describes a different bug and no longer
matches the code.

This also drops a full listing per stream: casexattr_len() runs its own
listxattr on every call, so enumerating a file with N xattrs cost N
listings instead of one.

Fixes: 689f1eb3719d ("ksmbd: report actual xattr value length in stream enumeration")
Signed-off-by: Gael Blivet <gael.blivet@gmail.com>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
[ sashal: retained non-const struct mnt_idmap pointers to match the existing vfs_getxattr() API ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/server/smb2pdu.c | 13 ++-----------
 fs/smb/server/vfs.c     |  4 ++--
 fs/smb/server/vfs.h     |  2 ++
 3 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index a8a42fde4ca02..12e73fa159fc0 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -5275,17 +5275,8 @@ static int get_file_stream_info(struct ksmbd_work *work,
 		streamlen *= 2;
 		kfree(stream_buf);
 		file_info->StreamNameLength = cpu_to_le32(streamlen);
-		/*
-		 * stream_name_len is the byte length of the xattr's *name*,
-		 * not its value -- same class of bug ksmbd_stream_eof()
-		 * (smb2pdu.c) already fixes for EndOfFile/AllocationSize on
-		 * a stream handle; this enumeration path needs the same
-		 * real xattr value length, not the name length reused as a
-		 * size.
-		 */
-		slen = ksmbd_vfs_casexattr_len(file_mnt_idmap(fp->filp),
-						path->dentry, stream_name,
-						strlen(stream_name) + 1, NULL);
+		slen = ksmbd_vfs_xattr_len(file_mnt_idmap(fp->filp),
+					   path->dentry, stream_name);
 		ssize = slen < 0 ? 0 : (loff_t)slen;
 		file_info->StreamSize = cpu_to_le64(ssize);
 		file_info->StreamAllocationSize = cpu_to_le64(ssize);
diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 130dd0a4001f2..68781f7a060be 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -950,8 +950,8 @@ ssize_t ksmbd_vfs_listxattr(struct dentry *dentry, char **list)
 	return size;
 }
 
-static ssize_t ksmbd_vfs_xattr_len(struct mnt_idmap *idmap,
-				   struct dentry *dentry, char *xattr_name)
+ssize_t ksmbd_vfs_xattr_len(struct mnt_idmap *idmap,
+			    struct dentry *dentry, char *xattr_name)
 {
 	return vfs_getxattr(idmap, dentry, xattr_name, NULL, 0);
 }
diff --git a/fs/smb/server/vfs.h b/fs/smb/server/vfs.h
index e9a5798d7baed..ca5048ebb1308 100644
--- a/fs/smb/server/vfs.h
+++ b/fs/smb/server/vfs.h
@@ -106,6 +106,8 @@ ssize_t ksmbd_vfs_getxattr(struct mnt_idmap *idmap,
 			   struct dentry *dentry,
 			   char *xattr_name,
 			   char **xattr_buf);
+ssize_t ksmbd_vfs_xattr_len(struct mnt_idmap *idmap,
+			    struct dentry *dentry, char *xattr_name);
 ssize_t ksmbd_vfs_casexattr_len(struct mnt_idmap *idmap,
 				struct dentry *dentry, char *attr_name,
 				int attr_name_len, char *actual_name);
-- 
2.53.0