[PATCH 6.18.y] smb: client: require stable pages for SMB compression

[Sasha Levin <sashal@kernel.org>]

From: Paulo Alcantara <pc@manguebit.org>

[ Upstream commit 8667061cf99394526dd9c0ea2662e6bbc7ae7848 ]

Like signing, SMB compression builds the write payload from the pagecache
folios: should_compress() lets a write request through and smb_compress()
compresses those folios on the way to the socket.  If a buffered write
mutates a folio while a write subrequest is still in flight, the compressed
bytes no longer correspond to a consistent view of the data, and the server
silently stores corrupted contents - worse than the signed case, which at
least fails loudly with STATUS_ACCESS_DENIED.

Mark the mapping for stable writes when a write may be compressed, i.e. the
same condition should_compress() tests (compression negotiated and the share
allows compressed data), so netfs_perform_write() waits for writeback to
complete before modifying an in-flight folio.

Fixes: f046d71e84e1 ("smb: client: insert compression check/call on write requests")
Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Reviewed-by: David Howells <dhowells@redhat.com>
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
[ sashal: Replaced tcon references with direct cifs_sb_master_tcon(cifs_sb) lookups because the local variable is absent. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/client/inode.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index 7c638b8d5490f..c63c74dd9d434 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -87,7 +87,9 @@ static void cifs_set_ops(struct inode *inode)
 		else
 			inode->i_data.a_ops = &cifs_addr_ops;
 		mapping_set_large_folios(inode->i_mapping);
-		if (cifs_sb_master_tcon(cifs_sb)->ses->server->sign)
+		if (cifs_sb_master_tcon(cifs_sb)->ses->server->sign ||
+		    (cifs_sb_master_tcon(cifs_sb)->ses->server->compression.enabled &&
+		     (cifs_sb_master_tcon(cifs_sb)->share_flags & SMB2_SHAREFLAG_COMPRESS_DATA)))
 			mapping_set_stable_writes(inode->i_mapping);
 		break;
 	case S_IFDIR:
-- 
2.53.0