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From:   Shyam Prasad <Shyam.Prasad@microsoft.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Salvatore Bonaccorso <carnil@debian.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        Aurelien Aptel <aaptel@suse.com>,
        Steven French <Steven.French@microsoft.com>,
        Sasha Levin <sashal@kernel.org>
Subject: RE: [EXTERNAL] Re: [PATCH 4.19 013/247] cifs: Set
 CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.
Thread-Topic: [EXTERNAL] Re: [PATCH 4.19 013/247] cifs: Set
 CIFS_MOUNT_USE_PREFIX_PATH flag on setting cifs_sb->prepath.
Thread-Index: AQHXKtl3oEpPTTCadkuXKYVCCMdGI6qnf4aAgAACKFA=
Date:   Tue, 6 Apr 2021 14:00:48 +0000
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Hi Greg,
We'll need to debug this further to understand what's going on.=20

Hi Salvatore,
Any chance that you'll be able to provide us the cifsFYI logs from the time=
 of mount failure?
https://wiki.samba.org/index.php/LinuxCIFS_troubleshooting#Enabling_Debuggi=
ng

Regards,
Shyam

-----Original Message-----
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>=20
Sent: Tuesday, April 6, 2021 7:12 PM
To: Salvatore Bonaccorso <carnil@debian.org>
Cc: linux-kernel@vger.kernel.org; stable@vger.kernel.org; Shyam Prasad <Shy=
am.Prasad@microsoft.com>; Aurelien Aptel <aaptel@suse.com>; Steven French <=
Steven.French@microsoft.com>; Sasha Levin <sashal@kernel.org>
Subject: [EXTERNAL] Re: [PATCH 4.19 013/247] cifs: Set CIFS_MOUNT_USE_PREFI=
X_PATH flag on setting cifs_sb->prepath.

On Tue, Apr 06, 2021 at 01:38:24PM +0200, Salvatore Bonaccorso wrote:
> Hi,
>=20
> On Mon, Mar 01, 2021 at 05:10:33PM +0100, Greg Kroah-Hartman wrote:
> > From: Shyam Prasad N <sprasad@microsoft.com>
> >=20
> > [ Upstream commit a738c93fb1c17e386a09304b517b1c6b2a6a5a8b ]
> >=20
> > While debugging another issue today, Steve and I noticed that if a=20
> > subdir for a file share is already mounted on the client, any new=20
> > mount of any other subdir (or the file share root) of the same share=20
> > results in sharing the cifs superblock, which e.g. can result in=20
> > incorrect device name.
> >=20
> > While setting prefix path for the root of a cifs_sb,=20
> > CIFS_MOUNT_USE_PREFIX_PATH flag should also be set.
> > Without it, prepath is not even considered in some places, and=20
> > output of "mount" and various /proc/<>/*mount* related options can=20
> > be missing part of the device name.
> >=20
> > Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
> > Reviewed-by: Aurelien Aptel <aaptel@suse.com>
> > Signed-off-by: Steve French <stfrench@microsoft.com>
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> >  fs/cifs/connect.c | 1 +
> >  1 file changed, 1 insertion(+)
> >=20
> > diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c index=20
> > 6285085195c15..632249ce61eba 100644
> > --- a/fs/cifs/connect.c
> > +++ b/fs/cifs/connect.c
> > @@ -3882,6 +3882,7 @@ int cifs_setup_cifs_sb(struct smb_vol *pvolume_in=
fo,
> >  		cifs_sb->prepath =3D kstrdup(pvolume_info->prepath, GFP_KERNEL);
> >  		if (cifs_sb->prepath =3D=3D NULL)
> >  			return -ENOMEM;
> > +		cifs_sb->mnt_cifs_flags |=3D CIFS_MOUNT_USE_PREFIX_PATH;
> >  	}
> > =20
> >  	return 0;
>=20
> A user in Debian reported an issue with mounts of DFS shares after an=20
> update in Debian from 4.19.177 to 4.181:
>=20
> https://nam06.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Flist
> s.debian.org%2Fdebian-user%2F2021%2F04%2Fmsg00062.html&amp;data=3D04%7C0
> 1%7CShyam.Prasad%40microsoft.com%7C0acbccd2643f4d55c6d008d8f901c180%7C
> 72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637533133251645484%7CUnknow
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> pttjbZJas%3D&amp;reserved=3D0
>=20
> In a test setup i was able to reproduce the issue with 4.19.184 itself=20
> (but interestingly not withing the 5.10.y series, checked 5.10.26)=20
> which both contain the above commit.
>=20
> 4.19.184 with a738c93fb1c1 ("cifs: Set CIFS_MOUNT_USE_PREFIX_PATH flag=20
> on setting cifs_sb->prepath.") reverted fixes the issue.
>=20
> Is there probably some missing prerequisites missing in the 4.19.y=20
> brach? I could not test othr versions, but maybe other versions are=20
> affected as well as before 4.19.y, as the commit was backported to
> 4.14.223 as well.

If there is a missing patch, we will be glad to take it, does 5.4 also have=
 this problem?

thanks,

greg k-h