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

[Steve French]

tentatively merged into cifs-2.6.git for-next pending testing and any
more review feedback

On Wed, Jun 16, 2021 at 1:09 AM ronnie sahlberg
<ronniesahlberg@xxxxxxxxx> wrote:
>
> Looks good to me.
>
> Acked-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
>
> On Wed, Jun 16, 2021 at 2:44 AM Thiago Rafael Becker <trbecker@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >  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
> >



-- 
Thanks,

Steve