smb: client: fix compound alignment with encryption

JIRA: https://issues.redhat.com/browse/RHEL-108683

commit 90f7c10
Author: Paulo Alcantara <pc@manguebit.org>
Date:   Sat Sep 6 21:19:29 2025 -0300

    smb: client: fix compound alignment with encryption
    
    The encryption layer can't handle the padding iovs, so flatten the
    compound request into a single buffer with required padding to prevent
    the server from dropping the connection when finding unaligned
    compound requests.
    
    Fixes: bc925c1 ("smb: client: improve compound padding in encryption")
    Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
    Reviewed-by: David Howells <dhowells@redhat.com>
    Cc: linux-cifs@vger.kernel.org
    Cc: stable@vger.kernel.org
    Signed-off-by: Steve French <stfrench@microsoft.com>

Signed-off-by: Paulo Alcantara <paalcant@redhat.com>

Author: pcacjr

fs/smb/client/smb2ops.c

@@ -2631,13 +2631,35 @@ smb2_set_next_command(struct cifs_tcon *tcon, struct smb_rqst *rqst)
 	}
 
 	/* SMB headers in a compound are 8 byte aligned. */
-	if (!IS_ALIGNED(len, 8)) {
-		num_padding = 8 - (len & 7);
+	if (IS_ALIGNED(len, 8))
+		goto out;
+
+	num_padding = 8 - (len & 7);
+	if (smb3_encryption_required(tcon)) {
+		int i;
+
+		/*
+		 * Flatten request into a single buffer with required padding as
+		 * the encryption layer can't handle the padding iovs.
+		 */
+		for (i = 1; i < rqst->rq_nvec; i++) {
+			memcpy(rqst->rq_iov[0].iov_base +
+			       rqst->rq_iov[0].iov_len,
+			       rqst->rq_iov[i].iov_base,
+			       rqst->rq_iov[i].iov_len);
+			rqst->rq_iov[0].iov_len += rqst->rq_iov[i].iov_len;
+		}
+		memset(rqst->rq_iov[0].iov_base + rqst->rq_iov[0].iov_len,
+		       0, num_padding);
+		rqst->rq_iov[0].iov_len += num_padding;
+		rqst->rq_nvec = 1;
+	} else {
 		rqst->rq_iov[rqst->rq_nvec].iov_base = smb2_padding;
 		rqst->rq_iov[rqst->rq_nvec].iov_len = num_padding;
 		rqst->rq_nvec++;
-		len += num_padding;
 	}
+	len += num_padding;
+out:
 	shdr->NextCommand = cpu_to_le32(len);
 }