[PATCH] cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.

[PATCH] cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.

[Shyam Prasad N]

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While debugging another issue today, Steve and I noticed that if a
subdir for a file share is already mounted on the client, any new
mount of any other subdir (or the file share root) results in sharing
the cifs superblock.
This could likely result in issues in other code paths as well.

Based on cursory code review, I think the CIFS_MOUNT_USE_PREFIX_PATH
flag is always used in conjunction with the cifs_sb->prepath field.
Attached patch sets this flag as soon as the prepath field is set in cifs_sb.

Please let me know if any of the above assumptions are wrong, or if
more needs to be done as a part of this fix.

-- 
Regards,
Shyam

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From 3a1374f02d76866474958624e2c512a0fea393bc Mon Sep 17 00:00:00 2001
From: Shyam Prasad N <sprasad@microsoft.com>
Date: Thu, 11 Feb 2021 03:07:13 -0800
Subject: [PATCH] cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting
 cifs_sb->prepath.

While setting prefix path for the root of a cifs_sb, CIFS_MOUNT_USE_PREFIX_PATH
flag should also be set. Without it, prepath is not even considered in some places.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
---
 fs/cifs/connect.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 76e4d8d8b3a6..4bb9decbbf27 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2756,6 +2756,7 @@ int cifs_setup_cifs_sb(struct cifs_sb_info *cifs_sb)
 		cifs_sb->prepath = kstrdup(ctx->prepath, GFP_KERNEL);
 		if (cifs_sb->prepath == NULL)
 			return -ENOMEM;
+		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_USE_PREFIX_PATH;
 	}
 
 	return 0;
-- 
2.25.1

Re: [PATCH] cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.

[Aurélien Aptel]

Shyam Prasad N <nspmangalore@gmail.com> writes:
> Please let me know if any of the above assumptions are wrong, or if
> more needs to be done as a part of this fix.

I think that's correct.

Reviewed-by: Aurelien Aptel <aaptel@suse.com>

-- 
Aurélien Aptel / SUSE Labs Samba Team
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