Bug 2259257

Could you please add details on exact mount options and autofs/systemd configuration?

cifs.upcall is called by the kernel's cifs.ko/smb3.ko drivers, so their mount options would influence the calls.

It may well be that some daemon tries to access the share to be automounted as root prior to user's access.

Certainly,

The systemd .mount contains
Type=smb3
Options=_netdev,sec=krb5,multiuser,nounix,noserverino,file_mode=0770,dir_mode=0770,nosfu,vers=3.0
in the mount section

the automount unit is configured for the mountpoint the mount unit defines.

My test with autofs uses the same mount arguments as the systemd mount unit.

The last time this is verified to work was somewhere around fc34 or fc35. On the off chance it was a kernel change I installed the latest 5.15 kernel from kernel.org. Same behavior. I'll pull the actual source for the latest fc34 kernel just in case it is the result of some backported fix.

Interesting. It is the kernel client. So with 5.15.148 the issue persists, but with 5.13.12-200.fc34.x86_64 it works as we expect.

From the logs a notable difference when attempting to access a directory in the dfs structure that refers to a path on an actual host it shows:
kernel: CIFS: Attempting to mount \\<dfs host>\<dfs root>
instead of the non functional kernel:
kernel: CIFS: Attempting to mount //<dfs host>/<dfs root>/<folder in dfs root>/<dfs ptr to actual share>

moving forward in time and attempting with 5.15.18-100.fc34.x86_64 it still works as we expect. So whatever broke it was something that was also backported to 5.15.

Works in 6.1.18, broken in the next kernel release (6.2.7) for fc36.

Thank you for this research, Shane!

I'll talk to Steve (upstream cifs.ko maintainer) and ask him to look at this issue.

I'm working on bisecting 6.1 right now, hopefully I'll have results sometime today.

Shane, thanks for looking into this.

Does it work if you add 'cruid=$USER' to mount options?

Besides, can you provide the following from both working and
non-working kernels:

  # umount any existing CIFS shares in the system
  dmesg --clear
  modprobe dns_resolver
  modprobe cifs
  echo 'module cifs +p' > /sys/kernel/debug/dynamic_debug/control
  echo 'file fs/cifs/* +p' > /sys/kernel/debug/dynamic_debug/control
  echo 1 > /proc/fs/cifs/cifsFYI
  echo 1 > /sys/module/dns_resolver/parameters/debug
  echo 0 > /proc/sys/kernel/printk_ratelimit
  echo 0 > /proc/fs/cifs/dfscache
  tcpdump -s 0 -w trace.pcap port 445 & pid=$!
  sleep 3
  klist > trace.log
  # mount share
  sleep 3
  kill $pid
  echo "========" >> trace.log
  cat /proc/fs/cifs/DebugData >> trace.log
  echo "========" >> trace.log
  cat /proc/fs/cifs/dfscache >> trace.log
  echo "========" >> trace.log
  dmesg >> trace.log

Thanks.

Result of the bisect suggests 9fd29a5bae6e8f94b410374099a6fddb253d2d5f is the culprit.

Thanks for bisecting it.  Yeah, that was the commit I had in mind.

The problem seems related to the automounted DFS link inheriting *uid
and *gid values from the DFS root superblock without checking if they
were actually set.  That is, if the user didn't specify them, we would
need to set their new values for the filesystem context used for
automounting the DFS link.

Could you please check if below changes fix you issue

diff --git a/fs/smb/client/cifs_dfs_ref.c b/fs/smb/client/cifs_dfs_ref.c
index 020e71fe1454..1edb7bcc8b81 100644
--- a/fs/smb/client/cifs_dfs_ref.c
+++ b/fs/smb/client/cifs_dfs_ref.c
@@ -308,6 +308,10 @@ static struct vfsmount *cifs_dfs_do_automount(struct path *path)
 	tmp = *cur_ctx;
 	tmp.source = full_path;
 	tmp.UNC = tmp.prepath = NULL;
+	if (!tmp.cruid_specified)
+		tmp.cred_uid = current_fsuid();
+	tmp.linux_uid = current_fsuid();
+	tmp.linux_gid = current_fsgid();
 
 	rc = smb3_fs_context_dup(ctx, &tmp);
 	if (rc) {

I believe I applied it correctly to 6.6.14:

diff --git a/fs/smb/client/namespace.c b/fs/smb/client/namespace.c
index a6968573b775..5843d8da26e4 100644
--- a/fs/smb/client/namespace.c
+++ b/fs/smb/client/namespace.c
@@ -206,6 +206,11 @@ static struct vfsmount *cifs_do_automount(struct path *path)
        tmp.UNC = tmp.prepath = NULL;
        tmp.dfs_root_ses = NULL;
 
+       if (!tmp.cruid_specified)
+               tmp.cred_uid = current_fsuid();
+       tmp.linux_uid = current_fsuid();
+       tmp.linux_gid = current_fsgid();
+
        rc = smb3_fs_context_dup(ctx, &tmp);
        if (rc) {
                mnt = ERR_PTR(rc);

and it indeed does work as I would like, thank you!

(In reply to Shane Nehring from comment #11)
> I believe I applied it correctly to 6.6.14:
> 
> diff --git a/fs/smb/client/namespace.c b/fs/smb/client/namespace.c
> index a6968573b775..5843d8da26e4 100644
> --- a/fs/smb/client/namespace.c
> +++ b/fs/smb/client/namespace.c
> @@ -206,6 +206,11 @@ static struct vfsmount *cifs_do_automount(struct path
> *path)
>         tmp.UNC = tmp.prepath = NULL;
>         tmp.dfs_root_ses = NULL;
>  
> +       if (!tmp.cruid_specified)
> +               tmp.cred_uid = current_fsuid();
> +       tmp.linux_uid = current_fsuid();
> +       tmp.linux_gid = current_fsgid();
> +
>         rc = smb3_fs_context_dup(ctx, &tmp);
>         if (rc) {
>                 mnt = ERR_PTR(rc);

LGTM.

> and it indeed does work as I would like, thank you!

Thanks for testing it!  I'll send it usptream and make sure that it
goes through -stable as well.

FYI, submitted fix upstream [1].

Maintainer merged it into his for-next branch as of 4508ec173570 [2]
and marked it for -stable.

[1] https://lore.kernel.org/all/20240211231931.185193-1-pc@manguebit.com/
[2] https://git.samba.org/?p=sfrench/cifs-2.6.git;a=commit;h=4508ec17357094e2075f334948393ddedbb75157

FEDORA-2024-88847bc77a (kernel-6.7.5-200.fc39) has been submitted as an update to Fedora 39.
https://bodhi.fedoraproject.org/updates/FEDORA-2024-88847bc77a

FEDORA-2024-987089eca2 (kernel-6.7.5-100.fc38) has been submitted as an update to Fedora 38.
https://bodhi.fedoraproject.org/updates/FEDORA-2024-987089eca2

FEDORA-2024-88847bc77a has been pushed to the Fedora 39 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2024-88847bc77a`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2024-88847bc77a

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-2024-987089eca2 has been pushed to the Fedora 38 testing repository.
Soon you'll be able to install the update with the following command:
`sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2024-987089eca2`
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2024-987089eca2

See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.

FEDORA-2024-88847bc77a (kernel-6.7.5-200.fc39) has been pushed to the Fedora 39 stable repository.
If problem still persists, please make note of it in this bug report.

FEDORA-2024-987089eca2 (kernel-6.7.5-100.fc38) has been pushed to the Fedora 38 stable repository.
If problem still persists, please make note of it in this bug report.