Re: [PATCH] cifs: retry lookup and readdir when EAGAIN is returned.

[ronnie sahlberg <ronniesahlberg@gmail.com>]

Looks good to me.

Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>

On Wed, Jun 16, 2021 at 2:44 AM Thiago Rafael Becker <trbecker@gmail.com> wrote:
>
> 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 apropriate
>         $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>
> ---
>  fs/cifs/dir.c     | 4 ++++
>  fs/cifs/smb2ops.c | 5 +++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
> index 6bcd3e8f7cda..7c641f9a3dac 100644
> --- a/fs/cifs/dir.c
> +++ b/fs/cifs/dir.c
> @@ -630,6 +630,7 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
>         struct inode *newInode = NULL;
>         const char *full_path;
>         void *page;
> +       int retry_count = 0;
>
>         xid = get_xid();
>
> @@ -673,6 +674,7 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
>         cifs_dbg(FYI, "Full path: %s inode = 0x%p\n",
>                  full_path, d_inode(direntry));
>
> +again:
>         if (pTcon->posix_extensions)
>                 rc = smb311_posix_get_inode_info(&newInode, full_path, parent_dir_inode->i_sb, xid);
>         else if (pTcon->unix_ext) {
> @@ -687,6 +689,8 @@ cifs_lookup(struct inode *parent_dir_inode, struct dentry *direntry,
>                 /* since paths are not looked up by component - the parent
>                    directories are presumed to be good here */
>                 renew_parental_timestamps(direntry);
> +       } else if (rc == -EAGAIN && retry_count++ < 10) {
> +               goto again;
>         } else if (rc == -ENOENT) {
>                 cifs_set_time(direntry, jiffies);
>                 newInode = NULL;
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 21ef51d338e0..d241e6af8fe4 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -2325,6 +2325,7 @@ smb2_query_dir_first(const unsigned int xid, struct cifs_tcon *tcon,
>         struct smb2_query_directory_rsp *qd_rsp = NULL;
>         struct smb2_create_rsp *op_rsp = NULL;
>         struct TCP_Server_Info *server = cifs_pick_channel(tcon->ses);
> +       int retry_count = 0;
>
>         utf16_path = cifs_convert_path_to_utf16(path, cifs_sb);
>         if (!utf16_path)
> @@ -2372,10 +2373,14 @@ smb2_query_dir_first(const unsigned int xid, struct cifs_tcon *tcon,
>
>         smb2_set_related(&rqst[1]);
>
> +again:
>         rc = compound_send_recv(xid, tcon->ses, server,
>                                 flags, 2, rqst,
>                                 resp_buftype, rsp_iov);
>
> +       if (rc == -EAGAIN && retry_count++ < 10)
> +               goto again;
> +
>         /* If the open failed there is nothing to do */
>         op_rsp = (struct smb2_create_rsp *)rsp_iov[0].iov_base;
>         if (op_rsp == NULL || op_rsp->sync_hdr.Status != STATUS_SUCCESS) {
> --
> 2.31.1
>