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Bug 2158724

Summary: systemd can send non-UTF8 messages over DBus, causing DBus to disconnect it
Product: Red Hat Enterprise Linux 8 Reporter: Renaud Métrich <rmetrich>
Component: systemdAssignee: Michal Sekletar <msekleta>
Status: CLOSED ERRATA QA Contact: Frantisek Sumsal <fsumsal>
Severity: high Docs Contact:
Priority: high    
Version: 8.7CC: bwelterl, dking, jamacku, kurathod, msekleta, qguo, systemd-maint-list
Target Milestone: rcKeywords: Triaged
Target Release: ---Flags: pm-rhel: mirror+
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: systemd-239-77.el8 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2023-11-14 15:48:25 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description Renaud Métrich 2023-01-06 10:20:41 UTC 
Description of problem:

This is a continuation of BZ #2158167 (related to PID recycling) and the condition making the latter be hit from time to time.

We have a customer seeing the scopes started for crond and sshd not getting destroyed inside systemd-logind when last PID exits.
This causes systemd-logind to "leak" sessions (state files remaining in /run/systemd/sessions in CLOSING state) and eventually systemd-logind to hit BZ #2158167 when PID recycling happens.
With the fix for BZ #2158167, the customer sees "Maximum number of sessions reached (8192)" after 1 day or so.

I requested an strace of systemd and systemd-logind to try to understand the condition where this would happen.
It appears the issue is due to having an issue within systemd which cannot abandon the scope:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
Scope session-50854.scope is not running, cannot abandon.
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Due to this, systemd-logind never deletes its internal data related to the session.

I don't know how to reproduce the condition for now. Comparing customer's strace and my strace, I see a lot of differences in DBus messages being issued by systemd to systemd-logind:

Customer:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
1     18:36:02.172067 sendmsg(19<UNIX:[397683477->397687257]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1H\0\0\0\24\35\3\0q\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\6\0\0\0JobNew\0\0\10\1g\0\3uos"..., iov_len=136}, {iov_base="\347.]\0%\0\0\0/org/freedesktop/systemd1/job/6106855\0\0\0\23\0\0\0session-50854.scope\0", iov_len=72}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 208 <0.000013>
1     18:36:02.179388 sendmsg(19<UNIX:[397683477->397687257]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1Q\0\0\0\26\35\3\0z\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\n\0\0\0JobRemoved\0\0\0\0\0\0"..., iov_len=144}, {iov_base="\347.]\0%\0\0\0/org/freedesktop/systemd1/job/6106855\0\0\0\23\0\0\0session-50854.scope\0\4\0\0\0done\0", iov_len=81}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 225 <0.000018>
1     18:36:02.623647 sendmsg(19<UNIX:[397683477->397687257]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\0015\0\0\0N\35\3\0o\0\0\0\1\1o\0\37\0\0\0/org/freedesktop/systemd1/agent\0\2\1s\0\36\0\0\0org.freedesktop.systemd1.Agent\0\0\3\1s\0\10\0\0\0Released\0\0\0\0\0\0\0\0\10\1g\0\1s\0\0", iov_len=128}, {iov_base="0\0\0\0/user.slice/user-11469.slice/session-50854.scope\0", iov_len=53}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 181 <0.000029>
1     18:36:02.628222 sendmsg(19<UNIX:[397683477->397687257]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\3\1\1>\0\0\0P\35\3\0_\0\0\0\5\1u\0\263i\0\0\6\1s\0\n\0\0\0:1.7022504\0\0\0\0\0\0\4\1s\0(\0\0\0org.freedesktop.systemd1.ScopeNotRunning\0\0\0\0\0\0\0\0\10\1g\0\1s\0\0", iov_len=112}, {iov_base="9\0\0\0Scope session-50854.scope is not running, cannot abandon.\0", iov_len=62}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 174 <0.000017>
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Mine:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
1     11:09:19.108569 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1K\0\0\0\365\0\0\0p\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\7\0\0\0UnitNew\0\10\1g\0\2so\0", iov_len=128}, {iov_base="\17\0\0\0session-3.scope\0002\0\0\0/org/freedesktop/systemd1/unit/session_2d3_2escope\0", iov_len=75}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL <unfinished ...>
1     11:09:19.108642 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1@\0\0\0\366\0\0\0q\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\6\0\0\0JobNew\0\0\10\1g\0\3uos"..., iov_len=136}, {iov_base="\240\2\0\0!\0\0\0/org/freedesktop/systemd1/job/672\0\0\0\17\0\0\0session-3.scope\0", iov_len=64}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL <unfinished ...>
1     11:09:19.113703 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1I\0\0\0\367\0\0\0z\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\n\0\0\0JobRemoved\0\0\0\0\0\0"..., iov_len=144}, {iov_base="\240\2\0\0!\0\0\0/org/freedesktop/systemd1/job/672\0\0\0\17\0\0\0session-3.scope\0\4\0\0\0done\0", iov_len=73}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 217 <0.000008>
1     11:09:19.225074 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1K\0\0\0\2\1\0\0x\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\v\0\0\0UnitRemoved\0\0\0\0\0"..., iov_len=136}, {iov_base="\17\0\0\0session-3.scope\0002\0\0\0/org/freedesktop/systemd1/unit/session_2d3_2escope\0", iov_len=75}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 211 <0.000013>
1     11:09:19.226435 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1-\0\0\0\3\1\0\0o\0\0\0\1\1o\0\37\0\0\0/org/freedesktop/systemd1/agent\0\2\1s\0\36\0\0\0org.freedesktop.systemd1.Agent\0\0\3\1s\0\10\0\0\0Released\0\0\0\0\0\0\0\0\10\1g\0\1s\0\0", iov_len=128}, {iov_base="(\0\0\0/user.slice/user-0.slice/session-3.scope\0", iov_len=45}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 173 <0.000019>
1     11:09:19.226783 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1K\0\0\0\5\1\0\0p\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\7\0\0\0UnitNew\0\10\1g\0\2so\0", iov_len=128}, {iov_base="\17\0\0\0session-3.scope\0002\0\0\0/org/freedesktop/systemd1/unit/session_2d3_2escope\0", iov_len=75}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL) = 203 <0.000015>
1     11:09:19.226857 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1K\0\0\0\6\1\0\0x\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\v\0\0\0UnitRemoved\0\0\0\0\0"..., iov_len=136}, {iov_base="\17\0\0\0session-3.scope\0002\0\0\0/org/freedesktop/systemd1/unit/session_2d3_2escope\0", iov_len=75}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL <unfinished ...>
1     11:09:19.227418 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1K\0\0\0\10\1\0\0p\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\7\0\0\0UnitNew\0\10\1g\0\2so\0", iov_len=128}, {iov_base="\17\0\0\0session-3.scope\0002\0\0\0/org/freedesktop/systemd1/unit/session_2d3_2escope\0", iov_len=75}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL <unfinished ...>
1     11:09:19.227492 sendmsg(51<UNIX:[17880->24141]>, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="l\4\1\1K\0\0\0\t\1\0\0x\0\0\0\1\1o\0\31\0\0\0/org/freedesktop/systemd1\0\0\0\0\0\0\0\2\1s\0 \0\0\0org.freedesktop.systemd1.Manager\0\0\0\0\0\0\0\0\3\1s\0\v\0\0\0UnitRemoved\0\0\0\0\0"..., iov_len=136}, {iov_base="\17\0\0\0session-3.scope\0002\0\0\0/org/freedesktop/systemd1/unit/session_2d3_2escope\0", iov_len=75}], msg_iovlen=2, msg_controllen=0, msg_flags=0}, MSG_DONTWAIT|MSG_NOSIGNAL <unfinished ...>
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

MAJOR DIFFERENCE: I don't see any UnitNew/UnitRemoved messages on customer's system


Version-Release number of selected component (if applicable):

systemd-239.68.el8
Suspected to be also seen on older systemd (we had a case with another customer in the past, before issue disappeared completely)

How reproducible:

Often/Always on customer system, cannot reproduce locally
Comment 16 Renaud Métrich 2023-01-20 12:38:51 UTC 
UPDATED DESCRIPTION:

The DBus message sent upon mounting a CIFS share can be broken, depending on the output of `/proc/self/mountinfo` and `/run/mount/utab` systemd relies on to build the message:
in case the CIFS share is presented by a NetApp appliance and contains non-ascii characters (e.g. "ü") and charset "iso8859-1" is used, systemd sends a non-UTF8 message through the bus, causing DBus to disconnect it.

Example of CIFS share listed in /proc/self/mountinfo (redacted):
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
//netapp.server/path/to/share/containing/umlaut_xxx�xxx /mount/point cifs rw,relatime,vers=3.0,xxx,iocharset=iso8859-1,xxx 0 0
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

I think we need to ensure that systemd always sends properly formatted messages to avoid any DBus breakage.

See also related BZs:
- #2162660 (DBus)
- #2162655 (Kernel/CIFS)
Comment 17 Renaud Métrich 2023-01-20 14:57:28 UTC 
REPRODUCER BELOW:

We can reproduce through having a CIFS share, which we then hack (using systemtap) to push a non-UTF8 character, see below.

CIFS setup (local):
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# yum -y install samba
# cat >> /etc/samba/smb.conf << EOF
[cifs]
	path = /cifs
	browseable = Yes
	read only = No
	guest ok = Yes
EOF

# mkdir -p /cifs/ssXss
# echo "//localhost/cifs/ssXss	/mnt			cifs	guest,noauto	0 0" >> /etc/fstab

# systemctl enable smb --now
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

SYSTEMTAP SCRIPT (let it run):
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# yum -y install systemtap
# stap-prep

# stap -v -g -e 'probe module("cifs").statement("cifs_show_devname@fs/cifs/cifsfs.c:480") { $devname[19] = 129; printf("new devname: %s\n", kernel_string_quoted($devname)); }'
...
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

The script replaces "ssXss" by "ssüss" once mount is done.

Corresponding source in kernel-4.18.0-425.10.1.el8_7.x86_64 (we are interested in hacking "devname" variable to report something not UTF8 in /proc/mounts):
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
 475 static int cifs_show_devname(struct seq_file *m, struct dentry *root)
 476 {
 477         struct cifs_sb_info *cifs_sb = CIFS_SB(root->d_sb);
 478         char *devname = kstrdup(cifs_sb->ctx->source, GFP_KERNEL);
 479 
 480         if (devname == NULL)
 481                 seq_puts(m, "none");
 482         else {
 483                 convert_delimiter(devname, '/');
 484                 /* escape all spaces in share names */
 485                 seq_escape(m, devname, " \t");
 486                 kfree(devname);
 487         }
 488         return 0;
 489 }
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

####################
 REPRODUCING STEPS:
####################

1. Check there is some "subscribed" client in systemd (i.e. systemd-logind)

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# gdb -ex "set pagination off" -ex "set confirm off" -ex "f 3" -ex "p m->subscribed" -ex "q" /usr/lib/systemd/systemd 1
[...]
#3  0x0000563e699efb62 in manager_loop (m=m@entry=0x563e6a06ae50) at ../src/core/manager.c:2898
2898	                r = sd_event_run(m->event, wait_usec);
$1 = (sd_bus_track *) 0x563e6a238130
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

2. Start systemtap and let it run

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# stap -v -g -e 'probe module("cifs").statement("cifs_show_devname@fs/cifs/cifsfs.c:480") { $devname[19] = 129; printf("new devname: %s\n", kernel_string_quoted($devname)); }'
...
Pass 5: starting run.
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

3. Mount the local CIFS share

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# mount /mnt
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

Systemtap will report:
new devname: "//localhost/cifs/ss\201ss"

showing it's hacking the output as planned.

4. Login on the system as a new user (to trigger some dbus traffic AND new mounts due to the new user)

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
$ ssh admin@localhost true
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

5. Check systemd got disconnected from the bus (it has no "subscribed" clients anymore)

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
# gdb -ex "set pagination off" -ex "set confirm off" -ex "f 3" -ex "p m->subscribed" -ex "q" /usr/lib/systemd/systemd 1
...
#3  0x0000563e699efb62 in manager_loop (m=m@entry=0x563e6a06ae50) at ../src/core/manager.c:2898
2898	                r = sd_event_run(m->event, wait_usec);
$1 = (sd_bus_track *) 0x0
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

At step 5 we see the leaks starts happening, sessions in /run/systemd/sessions are not destroyed anymore since systemd-logind doesn't receive notifications anymore:

# ssh admin@localhost true
# ssh admin@localhost true
# ssh admin@localhost true
# ll /run/systemd/sessions/
total 24
-rw-r--r-- 1 root root 322 Jan 20 15:49 1
-rw-r--r-- 1 root root 322 Jan 20 15:49 2
-rw-r--r-- 1 root root 306 Jan 20 15:54 5
-rw-r--r-- 1 root root 252 Jan 20 15:56 6
-rw-r--r-- 1 root root 252 Jan 20 15:56 7
-rw-r--r-- 1 root root 252 Jan 20 15:56 8
Comment 18 Plumber Bot 2023-07-13 22:12:00 UTC 
fix merged to github main branch -> https://github.com/redhat-plumbers/systemd-rhel8/pull/389
Comment 24 errata-xmlrpc 2023-11-14 15:48:25 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (systemd bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2023:7097