[PATCH 3/5] cifs: negotiate chained SMB2 compression capabilities

[Namjae Jeon <linkinjeon@kernel.org>]

Advertise LZ77 and Pattern_V1 with chained transform support in the
SMB 3.1.1 compression negotiate context. Validate the server's returned
algorithm list and flags, then retain the negotiated capabilities for a
future compressed transform receive implementation.

This patch only negotiates capabilities. It does not request compressed
READ responses or add a compressed transform receive path.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/smb/client/cifsglob.h |  2 ++
 fs/smb/client/smb2pdu.c  | 44 ++++++++++++++++++++++++++++++++--------
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 82e0adc1dabd..a3ac4aa4bbc6 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -789,6 +789,8 @@ struct TCP_Server_Info {
 	struct {
 		bool requested; /* "compress" mount option set*/
 		bool enabled; /* actually negotiated with server */
+		bool chained; /* chained transforms were negotiated */
+		bool pattern; /* Pattern_V1 chained payloads were negotiated */
 		__le16 alg; /* preferred alg negotiated with server */
 	} compression;
 	__u16	signing_algorithm;
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index fbeb2156ddb6..a79d8e6091d0 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -636,10 +636,16 @@ build_compression_ctxt(struct smb2_compression_capabilities_context *pneg_ctxt)
 	pneg_ctxt->DataLength =
 		cpu_to_le16(sizeof(struct smb2_compression_capabilities_context)
 			  - sizeof(struct smb2_neg_context));
-	pneg_ctxt->CompressionAlgorithmCount = cpu_to_le16(3);
+	/*
+	 * Pattern_V1 is useful only as part of a chained transform. LZ77 remains
+	 * the preferred general-purpose algorithm selected by this client.
+	 */
+	pneg_ctxt->CompressionAlgorithmCount = cpu_to_le16(4);
+	pneg_ctxt->Flags = SMB2_COMPRESSION_CAPABILITIES_FLAG_CHAINED;
 	pneg_ctxt->CompressionAlgorithms[0] = SMB3_COMPRESS_LZ77;
 	pneg_ctxt->CompressionAlgorithms[1] = SMB3_COMPRESS_LZ77_HUFF;
 	pneg_ctxt->CompressionAlgorithms[2] = SMB3_COMPRESS_LZNT1;
+	pneg_ctxt->CompressionAlgorithms[3] = SMB3_COMPRESS_PATTERN;
 }
 
 static unsigned int
@@ -827,9 +833,12 @@ static void decode_compress_ctx(struct TCP_Server_Info *server,
 			 struct smb2_compression_capabilities_context *ctxt)
 {
 	unsigned int len = le16_to_cpu(ctxt->DataLength);
-	__le16 alg;
+	unsigned int count, i;
 
 	server->compression.enabled = false;
+	server->compression.chained = false;
+	server->compression.pattern = false;
+	server->compression.alg = SMB3_COMPRESS_NONE;
 
 	/*
 	 * Caller checked that DataLength remains within SMB boundary. We still
@@ -841,20 +850,37 @@ static void decode_compress_ctx(struct TCP_Server_Info *server,
 		return;
 	}
 
-	if (le16_to_cpu(ctxt->CompressionAlgorithmCount) != 1) {
+	count = le16_to_cpu(ctxt->CompressionAlgorithmCount);
+	if (!count || count > ARRAY_SIZE(ctxt->CompressionAlgorithms) ||
+	    len < 8 + count * sizeof(__le16)) {
 		pr_warn_once("invalid SMB3 compress algorithm count\n");
 		return;
 	}
 
-	alg = ctxt->CompressionAlgorithms[0];
-
-	/* 'NONE' (0) compressor type is never negotiated */
-	if (alg == 0 || le16_to_cpu(alg) > 3) {
-		pr_warn_once("invalid compression algorithm '%u'\n", alg);
+	if (ctxt->Flags != SMB2_COMPRESSION_CAPABILITIES_FLAG_NONE &&
+	    ctxt->Flags != SMB2_COMPRESSION_CAPABILITIES_FLAG_CHAINED) {
+		pr_warn_once("invalid SMB3 compression flags\n");
 		return;
 	}
 
-	server->compression.alg = alg;
+	for (i = 0; i < count; i++) {
+		/* Record the intersection supported by the shared SMB codec. */
+		if (ctxt->CompressionAlgorithms[i] == SMB3_COMPRESS_LZ77)
+			server->compression.alg = SMB3_COMPRESS_LZ77;
+		else if (ctxt->CompressionAlgorithms[i] == SMB3_COMPRESS_PATTERN)
+			server->compression.pattern = true;
+	}
+	if (server->compression.alg != SMB3_COMPRESS_LZ77)
+		return;
+
+	/*
+	 * Pattern_V1 cannot appear in an unchained transform even if a broken
+	 * peer lists it in the algorithm array.
+	 */
+	server->compression.chained =
+		ctxt->Flags == SMB2_COMPRESSION_CAPABILITIES_FLAG_CHAINED;
+	if (!server->compression.chained)
+		server->compression.pattern = false;
 	server->compression.enabled = true;
 }
 
-- 
2.25.1