ksmbd: skip fallocate for SMB2_CREATE_ALLOCATION_SIZE on a stream handle

smb2_open() calls vfs_fallocate(fp->filp, ...) unconditionally when a
client's CREATE request includes an AllocationSize create context.
For a stream handle, fp->filp refers to the base file's data fork
(streams are xattr-backed on the same underlying file, not separate
files), so this pre-allocates storage on the base file's actual data
instead of doing anything meaningful for the stream -- fallocate has
no applicability to an xattr-backed stream at all.

Skip the fallocate call for stream handles.

Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Gael Blivet <gael.blivet@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

1 files changed, 16 insertions, 7 deletions

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 1a81391e95ef..587cc095b07b 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -4097,13 +4097,22 @@ int smb2_open(struct ksmbd_work *work)
 			ksmbd_debug(SMB,
 				    "request smb2 create allocate size : %llu\n",
 				    alloc_size);
-			smb_break_all_levII_oplock(work, fp, 1);
-			err = vfs_fallocate(fp->filp, FALLOC_FL_KEEP_SIZE, 0,
-					    alloc_size);
-			if (err < 0)
-				ksmbd_debug(SMB,
-					    "vfs_fallocate is failed : %d\n",
-					    err);
+			/*
+			 * fp->filp is the base file's data fork for a stream
+			 * handle (streams are xattr-backed on the same
+			 * underlying file) -- fallocate has no meaning for a
+			 * stream and would otherwise pre-allocate storage on
+			 * the base file's data instead.
+			 */
+			if (!ksmbd_stream_fd(fp)) {
+				smb_break_all_levII_oplock(work, fp, 1);
+				err = vfs_fallocate(fp->filp, FALLOC_FL_KEEP_SIZE, 0,
+						    alloc_size);
+				if (err < 0)
+					ksmbd_debug(SMB,
+						    "vfs_fallocate is failed : %d\n",
+						    err);
+			}
 		}
 
 		context = smb2_find_context_vals(req, SMB2_CREATE_QUERY_ON_DISK_ID, 4);