Re: [screen-devel] screen cannot reattach to previous session

[Petr Hracek]

On 09/08/2015 06:26 PM, Amadeusz Sławiński wrote:
> On Tue, 8 Sep 2015 12:08:54 +0200
> Petr Hracek <address@hidden> wrote:
>
> > On 08/31/2015 07:41 PM, Amadeusz Sławiński wrote:
> > > > I have received a bug
> > > > https://bugzilla.redhat.com/show_bug.cgi?id=1253697
> > > > which causes that screen indefinite hangs.
> > > >
> > > > Strace is a part of the bug.
> > > > Did you ever discover this problem?
> > > >
> > > > This bug was discovered in screen-4.1.0.
> > > Hi,
> > >
> > > I recall that someone on irc had similar problem, it seemed like
> > > his /dev/pts was being mounted with wrong options
> > > it needed something like those mount options to work:
> > > "gid=5,mode=620" (group 5 being tty on my system).
> > >
> > > Amadeusz
> > Hi,
> >
> > they provided a options:
> >
> > /dev/pts mount:
> >
> > $ mount | grep pts
> > devpts on /dev/pts type devpts
> > (rw,nosuid,noexec,relatime,seclabel,gid=5,mode=620,ptmxmode=000)
> >
> > But it seems that it is not working still.
> >
> > What about ptmxmode?
> > Could it be relevant?
> Hi,
>
> I don't think so, mine is also 000.
> As far as I can see from bugreport it happens between updates.
> What was version before and after update?
> Also do you have somewhere diff between those versions?
>
> It can be that there is some difference in "struct msg" between
> versions which causes this problem.
>
> Does it only fails to reattach after update?
> By which I mean, does new sessions after update attach properly?
>
> Amadeusz
Finally I have got the reason why screen hangs.
It is caused by patch "LoginName too long".

See related report https://bugzilla.redhat.com/show_bug.cgi?id=1119794
Patch for this case was mentioned there.

Screen related bug is https://savannah.gnu.org/bugs/?21653
Patch which we used is 
http://www.mail-archive.com/address@hidden/msg00829.html
and another patch. 
https://lists.gnu.org/archive/html/screen-devel/2011-05/msg00000.html'
What is the correct one for this bug?

And unfortunately I have applied the wrong patch like:
diff --git a/acls.c b/acls.c
index b8a5af4..b8ef048 100644
--- a/acls.c
+++ b/acls.c
@@ -182,7 +182,7 @@ struct acluser **up;
 #endif
   (*up)->u_Esc = DefaultEsc;
   (*up)->u_MetaEsc = DefaultMetaEsc;
-  strncpy((*up)->u_name, name, 20);
+  strncpy((*up)->u_name, name, MAXLOGINLEN);
   (*up)->u_password = NULL;
   if (pass)
     (*up)->u_password = SaveStr(pass);
@@ -318,8 +318,8 @@ struct acluser **up;
     return UserAdd(name, pass, up);
   if (!strcmp(name, "nobody"))        /* he remains without password */
     return -1;
-  strncpy((*up)->u_password, pass ? pass : "", 20);
-  (*up)->u_password[20] = '\0';
+  strncpy((*up)->u_password, pass ? pass : "", MAXLOGINLEN);
+  (*up)->u_password[MAXLOGINLEN] = '\0';
   return 0;
 }
 #endif
diff --git a/acls.h b/acls.h
index 907e953..42c7c18 100644
--- a/acls.h
+++ b/acls.h
@@ -78,7 +78,7 @@ struct plop
 typedef struct acluser
 {
   struct acluser *u_next;        /* continue the main user list */
-  char u_name[20+1];        /* login name how he showed up */
+  char u_name[MAXLOGINLEN + 1];        /* login name how he showed up */
   char *u_password;        /* his password (may be NullStr). */
   int  u_checkpassword;        /* nonzero if this u_password is valid */
   int  u_detachwin;        /* the window where he last detached */
diff --git a/comm.c b/comm.c
index 5f4af8a..7705fcb 100644
--- a/comm.c
+++ b/comm.c
@@ -36,6 +36,7 @@
  */

 #include "config.h"
+#include "os.h"
 #include "acls.h"
 #include "comm.h"

diff --git a/display.h b/display.h
index b1ab748..a433e6d 100644
--- a/display.h
+++ b/display.h
@@ -73,7 +73,7 @@ struct display
   struct win *d_other;        /* pointer to other window */
   int   d_nonblock;        /* -1 don't block if obufmax reached */
                 /* >0: block after nonblock secs */
-  char  d_termname[40 + 1];    /* $TERM */
+  char  d_termname[MAXTERMLEN + 1];    /* $TERM */
   char    *d_tentry;        /* buffer for tgetstr */
   char    d_tcinited;        /* termcap inited flag */
   int    d_width, d_height;    /* width/height of the screen */
diff --git a/os.h b/os.h
index 5c17c83..92846ad 100644
--- a/os.h
+++ b/os.h
@@ -521,3 +521,8 @@ typedef struct fd_set { int fds_bits[1]; } fd_set;
  */
 #define IOSIZE        4096

+/* Changing those you won't be able to attach to your old sessions
+ * when changing those values in official tree don't forget to bump
+ * MSG_VERSION */
+#define MAXTERMLEN  50
+#define MAXLOGINLEN 256
diff --git a/process.c b/process.c
index 0769cbe..623bf87 100644
--- a/process.c
+++ b/process.c
@@ -2664,9 +2664,9 @@ int key;
       s = NULL;
       if (ParseSaveStr(act, &s))
     break;
-      if (strlen(s) >= 20)
+      if (strlen(s) >= MAXTERMLEN)
     {
-      OutputMsg(0, "%s: term: argument too long ( < 20)", rc_name);
+     OutputMsg(0, "%s: term: argument too long ( < %d)", rc_name, 
MAXTERMLEN);
       free(s);
       break;
     }
diff --git a/screen.c b/screen.c
index 1c88157..eda16a3 100644
--- a/screen.c
+++ b/screen.c
@@ -995,10 +995,10 @@ char **av;

   if (home == 0 || *home == '\0')
     home = ppp->pw_dir;
-  if (strlen(LoginName) > 20)
 #ifdef MULTIUSER
-  if (multi && strlen(multi) > 20)
+  if (multi && strlen(multi) > MAXLOGINLEN)
     Panic(0, "Screen owner name too long - sorry.");
 #endif
   if (strlen(home) > MAXPATHLEN - 25)
diff --git a/screen.h b/screen.h
index 1a388e3..b95f8a2 100644
--- a/screen.h
+++ b/screen.h
@@ -202,32 +202,32 @@ struct msg
       int nargs;
       char line[MAXPATHLEN];
       char dir[MAXPATHLEN];
-      char screenterm[20];    /* is screen really "screen" ? */
+     char screenterm[MAXTERMLEN];    /* is screen really "screen" ? */
     }
       create;
       struct
     {
-      char auser[20 + 1];    /* username */
+     char auser[MAXLOGINLEN + 1];    /* username */
       int apid;        /* pid of frontend */
       int adaptflag;    /* adapt window size? */
       int lines, columns;    /* display size */
       char preselect[20];
       int esc;        /* his new escape character unless -1 */
       int meta_esc;        /* his new meta esc character unless -1 */
-      char envterm[40 + 1];    /* terminal type */
+     char envterm[MAXTERMLEN + 1];    /* terminal type */
       int encoding;        /* encoding of display */
       int detachfirst;      /* whether to detach remote sessions first */
     }
       attach;
       struct
     {
-      char duser[20 + 1];    /* username */
+     char duser[MAXLOGINLEN + 1];    /* username */
       int dpid;        /* pid of frontend */
     }
       detach;
       struct
     {
-      char auser[20 + 1];    /* username */
+     char auser[MAXLOGINLEN + 1];    /* username */
       int nargs;
       char cmd[MAXPATHLEN];    /* command */
       int apid;        /* pid of frontend */
diff --git a/socket.c b/socket.c
index 45887fb..b4d2400 100644
--- a/socket.c
+++ b/socket.c
@@ -1528,7 +1528,7 @@ static void PasswordProcessInput __P((char *, int));

 struct pwdata {
   int l;
-  char buf[20 + 1];
+  char buf[MAXLOGINLEN + 1];
   struct msg m;
 };


Greetings.


--
Petr Hracek
Software Engineer
Developer Experience
Red Hat, Inc
Mob: +420777056169
email: address@hidden