[WIP PATCH] allow changing the password on remount in some cases

[Steve French <smfrench@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1080 bytes --]

cifs: Work-in-progress patch to allow changing password
 during remount

There are cases where a session is disconnected but we can
not reconnect successfully since the user's password has changed
on the server (or expired) and this case currently can not be fixed
without unmount and mounting again which is not always realistic to do.
This patch allows remount to change the password when the session
is disconnected.

This patch needs to be tested for cases where you have multiuser mounts
and to make sure that there are no cases where we are changing
passwords for a different user than the one for the master tcon's
session (cifs_sb->tcon->ses->username)

Future patches should also allow us to setup the keyring (cifscreds)
to have an "alternate password" so we would be able to change
the password before the session drops (without the risk of races
between when the password changes and the disconnect occurs -
ie cases where the old password is still needed because the new
password has not fully rolled out to all servers yet).

See attached patch


-- 
Thanks,

Steve

[-- Attachment #2: 0001-cifs-Work-in-progress-patch-to-allow-changing-passwo.patch --]
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From 8632fcc917c0c35281b4bf4d8cadd5f5aaa18741 Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Tue, 13 Feb 2024 00:40:01 -0600
Subject: [PATCH] cifs: Work-in-progress patch to allow changing password
 during remount

There are cases where a session is disconnected and password has changed
on the server (or expired) for this user and this currently can not
be fixed without unmount and mounting again.  This patch allows
remount to change the password when the session is disconnect.

It needs to be tested for cases where you have multiuser mounts
and to make sure that there are no cases where we are changing
passwords for a different user than the one for the master tcon's
session (cifs_sb->tcon->ses->username)

Future patches should also allow us to setup the keyring (cifscreds)
to have an "alternate password" so we would be able to change
the password before the session drops (without the risk of races
between when the password changes and the disconnect occurs -
ie cases where the old password is still needed because the new
password has not fully rolled out to all servers yet).

Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/smb/client/fs_context.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index aec8dbd1f9db..c7a0b2bd7a15 100644
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -772,7 +772,7 @@ static void smb3_fs_context_free(struct fs_context *fc)
  */
 static int smb3_verify_reconfigure_ctx(struct fs_context *fc,
 				       struct smb3_fs_context *new_ctx,
-				       struct smb3_fs_context *old_ctx)
+				       struct smb3_fs_context *old_ctx, bool need_recon)
 {
 	if (new_ctx->posix_paths != old_ctx->posix_paths) {
 		cifs_errorf(fc, "can not change posixpaths during remount\n");
@@ -798,8 +798,11 @@ static int smb3_verify_reconfigure_ctx(struct fs_context *fc,
 	}
 	if (new_ctx->password &&
 	    (!old_ctx->password || strcmp(new_ctx->password, old_ctx->password))) {
-		cifs_errorf(fc, "can not change password during remount\n");
-		return -EINVAL;
+		if (need_recon == false) {
+			cifs_errorf(fc,
+				    "can not change password of active session during remount\n");
+			return -EINVAL;
+		}
 	}
 	if (new_ctx->domainname &&
 	    (!old_ctx->domainname || strcmp(new_ctx->domainname, old_ctx->domainname))) {
@@ -843,9 +846,15 @@ static int smb3_reconfigure(struct fs_context *fc)
 	struct smb3_fs_context *ctx = smb3_fc2context(fc);
 	struct dentry *root = fc->root;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(root->d_sb);
+	struct cifs_ses *ses = cifs_sb_master_tcon(cifs_sb)->ses;
+	bool need_recon = false;
 	int rc;
 
-	rc = smb3_verify_reconfigure_ctx(fc, ctx, cifs_sb->ctx);
+	if ((ses->ses_status == SES_NEED_RECON) ||
+	    (ses->ses_status == SES_IN_SETUP))
+		need_recon = true;
+
+	rc = smb3_verify_reconfigure_ctx(fc, ctx, cifs_sb->ctx, need_recon);
 	if (rc)
 		return rc;
 
@@ -858,7 +867,12 @@ static int smb3_reconfigure(struct fs_context *fc)
 	STEAL_STRING(cifs_sb, ctx, UNC);
 	STEAL_STRING(cifs_sb, ctx, source);
 	STEAL_STRING(cifs_sb, ctx, username);
-	STEAL_STRING_SENSITIVE(cifs_sb, ctx, password);
+	if (need_recon == false)
+		STEAL_STRING_SENSITIVE(cifs_sb, ctx, password);
+	else  {
+		kfree_sensitive(ses->password);
+		ses->password = kstrdup(ctx->password, GFP_KERNEL);
+	}
 	STEAL_STRING(cifs_sb, ctx, domainname);
 	STEAL_STRING(cifs_sb, ctx, nodename);
 	STEAL_STRING(cifs_sb, ctx, iocharset);
-- 
2.40.1