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Thiago Rafael Becker 6efa994e35 cifs: retry lookup and readdir when EAGAIN is returned.
According to the investigation performed by Jacob Shivers at Red Hat,
cifs_lookup and cifs_readdir leak EAGAIN when the user session is
deleted on the server. Fix this issue by implementing a retry with
limits, as is implemented in cifs_revalidate_dentry_attr.

Reproducer based on the work by Jacob Shivers:

  ~~~
  $ cat readdir-cifs-test.sh
  #!/bin/bash

  # Install and configure powershell and sshd on the windows
  #  server as descibed in
  # https://docs.microsoft.com/en-us/windows-server/administration/openssh/openssh_overview
  # This script uses expect(1)

  USER=dude
  SERVER=192.168.0.2
  RPATH=root
  PASS='password'

  function debug_funcs {
  	for line in $@ ; do
  		echo "func $line +p" > /sys/kernel/debug/dynamic_debug/control
  	done
  }

  function setup {
  	echo 1 > /proc/fs/cifs/cifsFYI
  	debug_funcs wait_for_compound_request \
                smb2_query_dir_first cifs_readdir \
                compound_send_recv cifs_reconnect_tcon \
                generic_ip_connect cifs_reconnect \
                smb2_reconnect_server smb2_reconnect \
                cifs_readv_from_socket cifs_readv_receive
  	tcpdump -i eth0 -w cifs.pcap host 192.168.2.182 & sleep 5
  	dmesg -C
  }

  function test_call {
  	if [[ $1 == 1 ]] ; then
  		tracer="strace -tt -f -s 4096 -o trace-$(date -Iseconds).txt"
  	fi
        # Change the command here to anything appropriate
  	$tracer ls $2 > /dev/null
  	res=$?
  	if [[ $1 == 1 ]] ; then
  		if [[ $res == 0 ]] ; then
  			1>&2 echo success
  		else
  			1>&2 echo "failure ($res)"
  		fi
  	fi
  }

  mountpoint /mnt > /dev/null || mount -t cifs -o username=$USER,pass=$PASS //$SERVER/$RPATH /mnt

  test_call 0 /mnt/

  /usr/bin/expect << EOF
  	set timeout 60

  	spawn ssh $USER@$SERVER

  	expect "yes/no" {
  		send "yes\r"
  		expect "*?assword" { send "$PASS\r" }
  	} "*?assword" { send "$PASS\r" }

  	expect ">" { send "powershell close-smbsession -force\r" }
  	expect ">" { send "exit\r" }
  	expect eof
  EOF

  sysctl -w vm.drop_caches=2 > /dev/null
  sysctl -w vm.drop_caches=2 > /dev/null

  setup

  test_call 1 /mnt/
  ~~~

Signed-off-by: Thiago Rafael Becker <trbecker@gmail.com>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
History 2021-06-20 21:28:17 -05:00
arch A first set of urgent fixes to the FPU/XSTATE handling mess^W code. 2021-06-20 09:09:58 -07:00
block block-5.13-2021-05-22 2021-05-22 07:40:34 -10:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto async_xor: check src_offs is not NULL before updating it 2021-06-10 19:40:14 -07:00
Documentation RISC-V Fixes for 5.13-rc7 2021-06-19 08:45:34 -07:00
drivers A single fix for GICv3 to not take an interrupt in an NMI context. 2021-06-20 09:38:14 -07:00
fs
include cifs: decoding negTokenInit with generic ASN1 decoder 2021-06-20 21:28:17 -05:00
init pid: take a reference when initializing cad_pid 2021-06-05 08:58:11 -07:00
ipc ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry 2021-05-22 15:09:07 -10:00
kernel - A single fix to restore fairness between control groups with equal priority 2021-06-20 09:44:52 -07:00
lib lib: crc64: fix kernel-doc warning 2021-06-05 08:58:12 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm/sparse: fix check_usemap_section_nr warnings 2021-06-16 09:24:43 -07:00
net Networking fixes for 5.13-rc7, including fixes from wireless, bpf, 2021-06-18 18:55:29 -07:00
samples VFIO fixes for v5.13-rc5 2021-06-03 11:52:24 -07:00
scripts recordmcount: Correct st_shndx handling 2021-06-18 09:09:17 -04:00
security trusted-keys: match tpm_get_ops on all return paths 2021-05-12 22:36:37 +03:00
sound sound fixes for 5.13-rc6 2021-06-11 10:47:10 -07:00
tools tools headers UAPI: Sync linux/in.h copy with the kernel sources 2021-06-19 10:15:22 -03:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: VMX: update vcpu posted-interrupt descriptor when assigning device 2021-05-27 07:58:23 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: use private address for Michel Lespinasse 2021-06-05 08:58:12 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 5.13-rc7, including fixes from wireless, bpf, 2021-06-18 18:55:29 -07:00
Makefile Linux 5.13-rc7 2021-06-20 15:03:15 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.