[BusyBox 0002434]: Segmentation fault ls -l, ps

bugs at busybox.net bugs at busybox.net
Fri May 2 15:49:45 UTC 2008


A NOTE has been added to this issue. 
====================================================================== 
http://busybox.net/bugs/view.php?id=2434 
====================================================================== 
Reported By:                fingar
Assigned To:                BusyBox
====================================================================== 
Project:                    BusyBox
Issue ID:                   2434
Category:                   Other
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     assigned
====================================================================== 
Date Submitted:             03-06-2008 02:19 PST
Last Modified:              05-02-2008 08:49 PDT
====================================================================== 
Summary:                    Segmentation fault ls -l, ps
Description: 
I am running Busybox 1.9.1 on Linux 2.6.21.3. I am using codesourcery
compiler arm-none-linux-gnueabi and running on AT91SAM9260.

When I run ls -l or ps I get segmentation fault. I have tracked the
problem down to get_cached_username in libbb/procps.c but I can't get any
further.

I don't know if it is a problem with my /etc/passwd file or something in
Busybox.

Any help would be appreciated
====================================================================== 

---------------------------------------------------------------------- 
 kienvtran - 05-01-08 09:15  
---------------------------------------------------------------------- 
Ran into the exact same problem on the same HW/SW platform.  Attached is a
fix in the form of an updated libbb/bb_pwd.c source file. 

---------------------------------------------------------------------- 
 vda - 05-01-08 23:58  
---------------------------------------------------------------------- 
/* bb_getpwuid, bb_getgrgid:
  * bb_getXXXid(buf, bufsz, id) - copy user/group name or id
- *               as a string to buf, return user/group name or NULL
- * bb_getXXXid(NULL, 0, id) - return user/group name or NULL
- * bb_getXXXid(NULL, -1, id) - return user/group name or exit
+ *               as a string to buf, return user/group name
+ * bb_getXXXid(NULL, 0, id) - illegal
+ * bb_getXXXid(NULL, -1, id) - illegal
  */

id is broken now - coreutils/id.c:

puts((flags & JUST_USER) ? bb_getpwuid(NULL, -1, uid) : bb_getgrgid(NULL,
-1, gid));

It would be better if instead of half-baked dirty fix you'd actually
debugged the crash. 

---------------------------------------------------------------------- 
 vda - 05-02-08 00:46  
---------------------------------------------------------------------- 
To debug it:

bb_pwd.c:

static char* bb_getug(char *buffer, int bufsize, char *idname, long id,
char prefix)
{
        if (bufsize > 0) {
bb_error_msg("HERE1");
                assert(buffer != NULL);
                if (idname) {
bb_error_msg("HERE2");
                        return safe_strncpy(buffer, idname, bufsize);
                }
bb_error_msg("HERE3");
                snprintf(buffer, bufsize, "%ld", id);
        } else if (bufsize < 0 && !idname) {
bb_error_msg("HERE4");
                bb_error_msg_and_die("unknown %cid %ld", prefix, id);
        }
bb_error_msg("HERE5: return '%s'", idname);
        return idname;
}

Recompile, let it crash, and show the output.

 

---------------------------------------------------------------------- 
 fingar - 05-02-08 05:25  
---------------------------------------------------------------------- 
result of debug

# ps
  PID  Uid        VSZ Stat Command
ps: HERE1
ps: HERE2
Segmentation fault
# 

---------------------------------------------------------------------- 
 vda - 05-02-08 06:32  
---------------------------------------------------------------------- 
Wow... can you replace lines

bb_error_msg("HERE2");
                        return safe_strncpy(buffer, idname, bufsize);

with

bb_error_msg("HERE2 buffer:%p idname:%p bufsize:%d", buffer, idname,
bufsize);
bb_error_msg("HERE21 buffer:'%s'", buffer);
bb_error_msg("HERE22 idname:'%s'", idname);
                        safe_strncpy(buffer, idname, bufsize);
bb_error_msg("HERE23 returning '%s'", buffer);
                        return buffer;

 

---------------------------------------------------------------------- 
 kienvtran - 05-02-08 07:49  
---------------------------------------------------------------------- 
When I inserted debug statements like vda suggested, without modifying the
code, the bug DISAPPEARED.  In that case the outputs of "ls -l" and "ps"
were useless, as they were interspersed with debug statements.

Are there regression tests that I could run to ensure that I don't break
anything else?  Sorry about "id" breaking, I am kind of new at this. 

---------------------------------------------------------------------- 
 fingar - 05-02-08 08:49  
---------------------------------------------------------------------- 
replaced the code with the extra debug messages as vda suggested. output is
now
# ps    
  PID  Uid        VSZ Stat Command                                  
ps: HERE1         
ps: HERE2 buffer:0x944a4 idname 0x94510 bufsize 12                        
                         
ps: HERE21 buffer:''                    
ps: HERE22 idname:'root'
ps: HERE23 returning 'root'
    1 root       3000 S   init
    2 root            SWN [ksoftirqd/0]
    3 root            SW< [events/0]
    4 root            SW< [khelper]
    5 root            SW< [kthread]
   40 root            SW< [kblockd/0]
   44 root            SW< [khubd]
   46 root            SW< [kseriod]
   59 root            SW  [pdflush]
   60 root            SW  [pdflush]
   61 root            SW< [kswapd0]
   62 root            SW< [aio/0]
   64 root            SW< [jfsIO]
   65 root            SW< [jfsCommit]
   66 root            SW< [jfsSync]
  675 root            SW  [mtdblockd]
  712 root            SWN [jffs2_gcd_mtd1]
  720 root       3004 S   /sbin/syslogd -O /var/log/messages
  722 root       3004 S   /sbin/klogd
  728 root       3008 S   /bin/sh
  733 root       3008 R   ps
#

It works now. Is this a toolchain problem. If I remove the debug messages
is it likely other things will be broken? 

Issue History 
Date Modified   Username       Field                    Change               
====================================================================== 
03-06-08 02:19  fingar         New Issue                                    
03-06-08 02:19  fingar         Status                   new => assigned     
03-06-08 02:19  fingar         Assigned To               => BusyBox         
05-01-08 09:15  kienvtran      Note Added: 0007334                          
05-01-08 09:15  kienvtran      File Added: bb_pwd.c                         
05-01-08 23:58  vda            Note Added: 0007344                          
05-02-08 00:19  vda            Note Added: 0007354                          
05-02-08 00:46  vda            Note Edited: 0007354                         
05-02-08 05:25  fingar         Note Added: 0007364                          
05-02-08 06:30  vda            Note Added: 0007374                          
05-02-08 06:32  vda            Note Edited: 0007374                         
05-02-08 07:49  kienvtran      Note Added: 0007384                          
05-02-08 08:49  fingar         Note Added: 0007394                          
======================================================================




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