On Thu, Nov 9, 2023 at 4:43 AM Paulo Alcantara <pc@xxxxxxxxxxxxx> wrote:
>
> Eduard Bachmakov <e.bachmakov@xxxxxxxxx> writes:
>
> > When attempting to mount (mount.cifs version 7.0) a share using
> >
> > $ mount -t cifs -o
> > vers=3.1.1,cred=/home/u/.secret.txt,uid=1000,gid=100
> > //smb.server.example.com/scans /home/u/mnt
> >
> > it succeeds on 6.5.9:
> >
> > mount("//smb.server.example.com/scans", ".", "cifs", 0,
> > "ip=192.168.5.43,unc=\\\\smb.server.example.com\\scans,vers=3.1.1,uid=1000,gid=100,user=u,pass=mypassword")
> > = 0
> >
> > but fails on 6.0.0:
> >
> > mount("//smb.server.example.com/scans", ".", "cifs", 0,
> > "ip=192.168.5.43,unc=\\\\smb.server.example.com\\scans,vers=3.1.1,uid=1000,gid=100,user=u,pass=mypassword")
> > = -1 ENOKEY (Required key not available)
> >
> > (or ENOENT) though it still works with using the IP instead of the domain:
> >
> > mount("//192.168.5.43/scans", ".", "cifs", 0,
> > "ip=192.168.5.43,unc=\\\\192.168.5.43\\scans,vers=3.1.1,uid=1000,gid=100,user=u,pass=mypassword")
> > = 0
> >
> > Based on my reading ever since 348a04a ("smb: client: get rid of dfs
> > code dep in namespace.c") dfs_mount_share() is now calling
> > dns_resolve_server_name_to_ip() early and unconditionally. This can be
> > verified on a running system by enabling dns_resolver logging (echo 1
> > | sudo tee /sys/module/dns_resolver/parameters/debug + watch dmesg).
> > An additional DNS lookup is attempted in 6.0.0 that previously wasn't.
> > My best guess is that ENOENT is "didn't work" and ENOKEY means "didn't
> > work but cached".
>
> Yes, this is a regression. Commit assumed that there would be always a
> dns_resolver key set up on kernels built with CONFIG_CIFS_DFS_UPCALL=y
> so that cifs.ko could safely upcall to resolve UNC hostname regardless
> whether mounting a DFS share or a regular share.
>
> Could you please try attached patch?
Can confirm, this works. No more UMH DNS lookup, share is mounted successfully.
I don't see is_dfs_mount() being called so in my scenario we're simply
relying on kzalloc initializing dfs_automount to false.
> Thanks.
