[PATCH v2 6/9] smb/client: verify allocation after EOF-extending fallocate

[Huiwen He <huiwen.he@linux.dev>]

From: Huiwen He <hehuiwen@kylinos.cn>

EOF-extending fallocate(mode=0) currently returns success after SetEOF
even if the server has not allocated the requested space. This gives
userspace a false preallocation guarantee and can cause a later write
into that range to fail with ENOSPC.

This happens because SMB2 has no operation that directly matches Linux
fallocate for an arbitrary byte range. SetEOF changes only the logical
file size, while FILE_ALLOCATION_INFORMATION can request allocation only
from offset 0 up to a specified allocation size.

Use FILE_ALLOCATION_INFORMATION only when allocating [0, off + len)
safely covers the requested range [off, off + len). For example, both
ranges are identical when the request starts at offset zero:

        xfs_io -f -c "falloc 0 4m" file

Allocating the additional range before off is also safe for an empty
file:

        truncate -s 0 file
        xfs_io -c "falloc 1m 4m" file

An EOF-adjacent request is safe for a non-sparse file because the range
before EOF is already allocated:

        xfs_io -f -c "pwrite 0 1m" file
        xfs_io -c "falloc 1m 4m" file

Request and verify the resulting AllocationSize before extending EOF, so
an allocation failure leaves the file size unchanged. Reject other
non-zero-offset requests because AllocationSize cannot identify which
byte ranges were allocated.

With Samba `strict allocate=yes`, this allows generic/496, generic/568 and
generic/701 to pass after verifying the server allocation. With
`strict allocate=no`, the requests fail instead of reporting false
preallocation success.

Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
---
 fs/smb/client/smb2ops.c   | 69 +++++++++++++++++++++++++++++++++++----
 fs/smb/client/smb2pdu.c   | 19 +++++++++++
 fs/smb/client/smb2proto.h |  3 ++
 fs/smb/common/fscc.h      |  5 +++
 4 files changed, 90 insertions(+), 6 deletions(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index b8474ed9af16..20cc66f728a7 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3665,12 +3665,16 @@ static long smb3_simple_falloc(struct file *file, struct cifs_tcon *tcon,
 	struct cifsFileInfo *cfile = file->private_data;
 	long rc = -EOPNOTSUPP;
 	unsigned int xid;
-	loff_t new_eof;
+	loff_t old_eof, new_eof;
+	struct smb2_file_all_info file_inf;
+	u64 asize = 0;
+	int qrc;
 
 	xid = get_xid();
 
 	inode = d_inode(cfile->dentry);
 	cifsi = CIFS_I(inode);
+	old_eof = i_size_read(inode);
 
 	trace_smb3_falloc_enter(xid, cfile->fid.persistent_fid, tcon->tid,
 				tcon->ses->Suid, off, len);
@@ -3686,11 +3690,24 @@ static long smb3_simple_falloc(struct file *file, struct cifs_tcon *tcon,
 	/*
 	 * Extending the file
 	 */
-	if ((keep_size == false) && i_size_read(inode) < off + len) {
+	if (!keep_size && old_eof < off + len) {
 		rc = inode_newsize_ok(inode, off + len);
 		if (rc)
 			goto out;
 
+		/*
+		 * FILE_ALLOCATION_INFORMATION sets the allocation size for the whole
+		 * file and cannot allocate an arbitrary byte range. Use it only for
+		 * requests starting at offset zero, requests on an empty file, or
+		 * requests appending to a non-sparse file.
+		 */
+		if (off != 0 && old_eof != 0 &&
+		    (off != old_eof ||
+		     (cifsi->cifsAttrs & FILE_ATTRIBUTE_SPARSE_FILE))) {
+			rc = -EOPNOTSUPP;
+			goto out;
+		}
+
 		if (cifsi->cifsAttrs & FILE_ATTRIBUTE_SPARSE_FILE) {
 			rc = smb2_set_sparse(xid, tcon, cfile, inode, false);
 			if (rc)
@@ -3698,12 +3715,52 @@ static long smb3_simple_falloc(struct file *file, struct cifs_tcon *tcon,
 		}
 
 		new_eof = off + len;
+
+		qrc = SMB2_query_info(xid, tcon, cfile->fid.persistent_fid,
+				      cfile->fid.volatile_fid, &file_inf);
+		if (qrc == 0)
+			asize = le64_to_cpu(file_inf.AllocationSize);
+
+		if (qrc || asize < new_eof) {
+			rc = SMB2_set_allocation(xid, tcon,
+						 cfile->fid.persistent_fid,
+						 cfile->fid.volatile_fid,
+						 cfile->pid, new_eof);
+			if (rc)
+				goto invalidate_attrs;
+
+			qrc = SMB2_query_info(xid, tcon,
+					      cfile->fid.persistent_fid,
+					      cfile->fid.volatile_fid, &file_inf);
+			if (qrc) {
+				rc = qrc;
+				goto invalidate_attrs;
+			}
+
+			asize = le64_to_cpu(file_inf.AllocationSize);
+			if (asize < new_eof) {
+				rc = -EOPNOTSUPP;
+				goto invalidate_attrs;
+			}
+		}
+
 		rc = SMB2_set_eof(xid, tcon, cfile->fid.persistent_fid,
 				  cfile->fid.volatile_fid, cfile->pid, new_eof);
-		if (rc == 0) {
-			netfs_resize_file(&cifsi->netfs, new_eof, true);
-			cifs_setsize(inode, new_eof);
-		}
+		if (rc)
+			goto invalidate_attrs;
+
+		netfs_resize_file(&cifsi->netfs, new_eof, true);
+		cifs_setsize(inode, new_eof);
+
+		spin_lock(&inode->i_lock);
+		inode->i_blocks = CIFS_INO_BLOCKS(asize);
+		spin_unlock(&inode->i_lock);
+		goto out;
+
+invalidate_attrs:
+		spin_lock(&inode->i_lock);
+		cifsi->time = 0;
+		spin_unlock(&inode->i_lock);
 		goto out;
 	}
 
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 4972cfe249f6..1c6fadb7fbf3 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -5899,6 +5899,25 @@ SMB2_set_eof(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 			0, 1, &data, &size);
 }
 
+int
+SMB2_set_allocation(const unsigned int xid, struct cifs_tcon *tcon,
+		    u64 persistent_fid, u64 volatile_fid, u32 pid,
+		    loff_t allocation_size)
+{
+	struct smb2_file_alloc_info info;
+	void *data;
+	unsigned int size;
+
+	info.AllocationSize = cpu_to_le64(allocation_size);
+
+	data = &info;
+	size = sizeof(struct smb2_file_alloc_info);
+
+	return send_set_info(xid, tcon, persistent_fid, volatile_fid,
+			pid, FILE_ALLOCATION_INFORMATION, SMB2_O_INFO_FILE,
+			0, 1, &data, &size);
+}
+
 int
 SMB2_set_acl(const unsigned int xid, struct cifs_tcon *tcon,
 		u64 persistent_fid, u64 volatile_fid,
diff --git a/fs/smb/client/smb2proto.h b/fs/smb/client/smb2proto.h
index 78a4e1c340f9..16a02c1eb0a1 100644
--- a/fs/smb/client/smb2proto.h
+++ b/fs/smb/client/smb2proto.h
@@ -204,6 +204,9 @@ void SMB2_query_directory_free(struct smb_rqst *rqst);
 int SMB2_set_eof(const unsigned int xid, struct cifs_tcon *tcon,
 		 u64 persistent_fid, u64 volatile_fid, u32 pid,
 		 loff_t new_eof);
+int SMB2_set_allocation(const unsigned int xid, struct cifs_tcon *tcon,
+			u64 persistent_fid, u64 volatile_fid, u32 pid,
+			loff_t allocation_size);
 int SMB2_set_info_init(struct cifs_tcon *tcon, struct TCP_Server_Info *server,
 		       struct smb_rqst *rqst, u64 persistent_fid,
 		       u64 volatile_fid, u32 pid, u8 info_class, u8 info_type,
diff --git a/fs/smb/common/fscc.h b/fs/smb/common/fscc.h
index bc3012cc295d..c9d5aa94727f 100644
--- a/fs/smb/common/fscc.h
+++ b/fs/smb/common/fscc.h
@@ -265,6 +265,11 @@ struct smb2_file_eof_info { /* encoding of request for level 10 */
 	__le64 EndOfFile; /* new end of file value */
 } __packed; /* level 20 Set */
 
+/* See MS-FSCC 2.4.4 */
+struct smb2_file_alloc_info { /* encoding of request for level 19 */
+	__le64 AllocationSize;
+} __packed;
+
 /* See MS-FSCC 2.4.15 */
 typedef struct {
 	__le32 NextEntryOffset;
-- 
2.43.0