[PATCH v3 06/15] smb: client: flush and commit data before querying allocated ranges

[Paulo Alcantara <pc@manguebit.org>]

The mode 0 / FALLOC_FL_KEEP_SIZE fallocate emulation for small interior
ranges in smb3_simple_fallocate_range() issues
FSCTL_QUERY_ALLOCATED_RANGES and zero-fills any sub-range the server
reports as an unallocated hole, to force block allocation without
changing file contents.

This is unsafe against Windows servers.  Per the Win32 documentation,
FSCTL_QUERY_ALLOCATED_RANGES only reports ranges that *may* contain
nonzero data and is explicitly not coherent with recently written data:

  "a call to FSCTL_QUERY_ALLOCATED_RANGES [after writing to a network
   file] would not necessarily return a correct list of allocated
   regions.  To ensure coherency [...] flush the data to the file"

fsx (generic/363) reproduces the resulting corruption against Windows
Server 2022: a range is written, an uncached read returns the data, yet
the next FSCTL_QUERY_ALLOCATED_RANGES on that range reports it as a whole
hole, so the emulation overwrites live data with zeroes.  A network trace
confirmed the WRITE, the READ returning data and the query returning an
empty range list within microseconds.  Samba does not exhibit this; its
query is coherent with the written data.

Write back the dirty pages, drain any outstanding I/O and issue an SMB2
FLUSH to force the server to commit the data before querying the
allocated ranges, so the query reflects the data actually present.

With this, generic/363 passes against both Windows Server 2022 and Samba
over 100000 fsx operations.

Fixes: 966a3cb7c7db ("cifs: improve fallocate emulation")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org
---
 fs/smb/client/smb2ops.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 849cfd2de705..1c41d3b24c6d 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3750,6 +3750,24 @@ static int smb3_simple_fallocate_range(unsigned int xid,
 		goto out;
 	}
 
+	filemap_invalidate_lock(inode->i_mapping);
+
+	/*
+	 * Flush and commit the data to the server, otherwise
+	 * FSCTL_QUERY_ALLOCATED_RANGES might report recently written data as
+	 * unallocated holes on Windows Servers, and the loop below would
+	 * then zero-fill them and corrupt the file.
+	 */
+	rc = filemap_write_and_wait_range(inode->i_mapping, off,
+					  off + len - 1);
+	if (rc)
+		goto out_unlock;
+	netfs_wait_for_outstanding_io(inode);
+	rc = SMB2_flush(xid, tcon, cfile->fid.persistent_fid,
+			cfile->fid.volatile_fid);
+	if (rc)
+		goto out_unlock;
+
 	in_data.file_offset = cpu_to_le64(off);
 	in_data.length = cpu_to_le64(len);
 	rc = SMB2_ioctl(xid, tcon, cfile->fid.persistent_fid,
@@ -3759,7 +3777,7 @@ static int smb3_simple_fallocate_range(unsigned int xid,
 			1024 * sizeof(struct file_allocated_range_buffer),
 			(char **)&out_data, &out_data_len);
 	if (rc)
-		goto out;
+		goto out_unlock;
 
 	tmp_data = out_data;
 	while (len) {
@@ -3769,12 +3787,12 @@ static int smb3_simple_fallocate_range(unsigned int xid,
 		if (out_data_len == 0) {
 			rc = smb3_simple_fallocate_write_range(xid, tcon,
 					       cfile, off, len, buf);
-			goto out;
+			goto out_unlock;
 		}
 
 		if (out_data_len < sizeof(struct file_allocated_range_buffer)) {
 			rc = -EINVAL;
-			goto out;
+			goto out_unlock;
 		}
 
 		range_start = le64_to_cpu(tmp_data->file_offset);
@@ -3782,7 +3800,7 @@ static int smb3_simple_fallocate_range(unsigned int xid,
 		if (check_add_overflow(range_start, range_len, &range_end) ||
 		    range_end > S64_MAX) {
 			rc = -EINVAL;
-			goto out;
+			goto out_unlock;
 		}
 
 		if (off < range_start) {
@@ -3797,11 +3815,11 @@ static int smb3_simple_fallocate_range(unsigned int xid,
 			rc = smb3_simple_fallocate_write_range(xid, tcon,
 					       cfile, off, l, buf);
 			if (rc)
-				goto out;
+				goto out_unlock;
 			off = off + l;
 			len = len - l;
 			if (len == 0)
-				goto out;
+				goto out_unlock;
 		}
 		/*
 		 * We are at a section of allocated data, just skip forward
@@ -3820,6 +3838,8 @@ static int smb3_simple_fallocate_range(unsigned int xid,
 		out_data_len -= sizeof(struct file_allocated_range_buffer);
 	}
 
+ out_unlock:
+	filemap_invalidate_unlock(inode->i_mapping);
  out:
 	kfree(out_data);
 	kvfree(buf);
-- 
2.55.0