[Bug 1927745] Re: Non-thread-safe functions used in multi-threaded rpc.gssd

Mon May 10 16:24:37 UTC 2021

** Description changed:

  [Impact]
+ rpc-gssd can hang or crash when a kerberos nfsv4 mount point is accessed by multiple users simultaneously. This is caused because the daemon uses the strtok() function which is not thread safe.

-  * An explanation of the effects of the bug on users and
- 
-  * justification for backporting the fix to the stable release.
- 
-  * In addition, it is helpful, but not required, to include an
-    explanation of how the upload fixes this bug.
+ The fix from upstream removes strtok() and uses strsep() instead. These
+ patches are already applied in focal and later, via merges from debian.

  [Test Plan]
  # Create a bionic VM. Login and get its ip, and take note of it:
  export IP=$(ip route get default 8.8.8.8 | grep ^8 | awk '{print $7}')
  echo $IP

  # adjust /etc/hosts:
  echo "$IP $(hostname).example.com" | sudo tee -a /etc/hosts

  # adjust /etc/resolv.conf:
  echo "search example.com" | sudo tee -a /etc/resolv.conf

  # verify hostname -f returns the fqdn of the vm, i.e., a name with the .example.com domain:
  hostname -f

  # Run these commands, and when asked:
  # - for realm: EXAMPLE.COM
  # - for kdc and admin server: use the vm's IP

  sudo apt update && sudo apt install nfs-server krb5-kdc krb5-admin-
  server krb5-user gcc

  # create a kerberos realm. When prompted, use any password you want:
  sudo krb5_newrealm

  # create an nfs service ticket, and store it in the keytab
  sudo kadmin.local -q "addprinc -randkey nfs/$(hostname -f)"
  sudo kadmin.local -q "ktadd nfs/$(hostname -f)"

  # create test directories
  sudo mkdir -p /mnt/test_krb5/
  sudo mkdir -p /export
  sudo touch /export/foo

  # adjust nfs config and restart the nfs server:
  sudo sed -r -i "s,^NEED_SVCGSSD=.*,NEED_SVCGSSD=\"yes\"," /etc/default/nfs-kernel-server
  sudo sed -r -i "s,^NEED_GSSD=.*,NEED_GSSD=\"yes\"," /etc/default/nfs-common
  sudo systemctl restart nfs-server

  # configure an nfs export:
  echo "/export *(sec=krb5,rw,sync,no_subtree_check)" | sudo tee -a /etc/exports
  sudo exportfs -rva

  # confirm it's available
  sudo showmount -e localhost

  # mount it
  sudo mount $(hostname -f):/export /mnt/test_krb5/
  sudo ls -la /mnt/test_krb5

  # download bug attachments
  wget -ct0 https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/1927745/+attachment/5496166/+files/stat_as.c https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/1927745/+attachment/5496167/+files/bz1419280_test_threads
  chmod +x bz1419280_test_threads

  # build reproducer
  gcc stat_as.c -o stat_as

  # run test script as root. It may take a few minutes to trigger the bug
  sudo ./bz1419280_test_threads

  # wait
  # Once you get the confirmation:
  calling stat on '/mnt/test_krb5/foo' with uids 9995 through 10035
  reproduced the bug after 114 iterations

  # Check for a "stat_as" D state process:
  $ ps axw|grep stat_as
  17814 pts/1    D      0:00 ./stat_as /mnt/test_krb5/foo 9995 10035

  # With the updated packages, the script will not detect the bug and
  never stop.

  [Where problems could occur]

   * Think about what the upload changes in the software. Imagine the change is
     wrong or breaks something else: how would this show up?

   * It is assumed that any SRU candidate patch is well-tested before
     upload and has a low overall risk of regression, but it's important
     to make the effort to think about what ''could'' happen in the
     event of a regression.

   * This must '''never''' be "None" or "Low", or entirely an argument as to why
     your upload is low risk.

   * This both shows the SRU team that the risks have been considered,
     and provides guidance to testers in regression-testing the SRU.

  [Other Info]

   * Anything else you think is useful to include
   * Anticipate questions from users, SRU, +1 maintenance, security teams and the Technical Board
   * and address these questions in advance

  [Original Description]

  Fixed in focal and later, due to sync from debian

  Bionic affected.

  I'll add a proper description in a moment.

  RH: https://bugzilla.redhat.com/show_bug.cgi?id=1419280
  Debian BTS: https://bugs.debian.org/895381
  ML: http://www.spinics.net/lists/linux-nfs/msg62111.html
  ML: http://www.spinics.net/lists/linux-nfs/msg62099.html

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https://bugs.launchpad.net/bugs/1927745

Title:
  Non-thread-safe functions used in multi-threaded rpc.gssd

Status in nfs-utils package in Ubuntu:
  Fix Released
Status in nfs-utils source package in Bionic:
  In Progress
Status in nfs-utils package in Debian:
  Fix Released
Status in nfs-utils package in Fedora:
  Fix Released

Bug description:
  [Impact]
  rpc-gssd can hang or crash when a kerberos nfsv4 mount point is accessed by multiple users simultaneously. This is caused because the daemon uses the strtok() function which is not thread safe.

  The fix from upstream removes strtok() and uses strsep() instead.
  These patches are already applied in focal and later, via merges from
  debian.