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Prior to this update, the snmpd daemon did not detect errors when accessing the /proc file system. Consequent to this, an attempt to read information about an exited process while gathering information for a HOST-RESOURCES-MIB::hrSWRunTable table caused the daemon to terminate unexpectedly with a segmentation fault. This update adapts the underlying source code to make sure that such errors are now properly detected, and snmpd no longer crashes when populating HOST-RESOURCES-MIB::hrSWRunTable. (BZ#683563).
Created attachment 483274[details]
patch for reading pid-based /proc files
+++ This bug was initially created as a clone of Bug #683142 +++
Description of problem:
Customer is seeing SEGV in var_hrswrun() in host/hr_swrun.c to to failure to check fgets return code.
Version-Release number of selected component (if applicable):
net-snmp-5.3.2.2-5.el5
How reproducible:
Not easy, it require the tested process to terminate between snmpd opening and reading the status file.
--- Additional comment from mpoole on 2011-03-08 11:43:11 EST ---
-------------------------------------------------------------------------------
Core was generated by `/usr/sbin/snmpd -LS 5d -Lf /dev/null -p /var/run/snmpd.pid -a'.
Program terminated with signal 11, Segmentation fault.
[New process 7428]
[New process 7430]
#0 var_hrswrun (vp=0x7fff2954a070, name=<value optimized out>, length=<value optimized out>,
exact=<value optimized out>, var_len=<value optimized out>, write_method=<value optimized out>)
at host/hr_swrun.c:1152
1152 while (*cp != ' ')
-------------------------------------------------------------------------------
Here is a part of var_hrswrun() to review.
-------------------------------------------------------------------------------
461 u_char *
462 var_hrswrun(struct variable * vp,
463 oid * name,
464 size_t * length,
465 int exact, size_t * var_len, WriteMethod ** write_method)
466 {
<snip>
1143 #elif defined(linux)
1144 sprintf(string, "/proc/%d/stat", pid);
1145 if ((fp = fopen(string, "r")) == NULL) {
1146 long_return = 0;
1147 return (u_char *) & long_return;
1148 }
1149 fgets(buf, sizeof(buf), fp);
1150 cp = buf;
1151 for (i = 0; i < 23; ++i) { /* skip 23 fields */
1152 while (*cp != ' ')
1153 ++cp;
1154 ++cp;
1155 }
1156 long_return = atoi(cp) * (getpagesize() / 1024); /* rss
*/
1157 fclose(fp);
-------------------------------------------------------------------------------
--- Additional comment from mpoole on 2011-03-08 12:27:01 EST ---
Although it is possible to fix just this single error it is but one example of a systemic failure to perform return code checks for a number of other reads of /proc/<pid> files.
I am currently working through the set attempting a composite patch.
--- Additional comment from mpoole on 2011-03-09 10:42:51 EST ---
Created attachment 483247[details]
patch for reading pid-based /proc files
--- Additional comment from mpoole on 2011-03-09 10:45:23 EST ---
Upstream for a single instance fix of the proc race condition is at
http://sourceforge.net/tracker/index.php?func=detail&aid=1774612&group_id=12694&atid=312694
The patch I've just attached here fixes all the /proc/<pid>/? read blocks.
Technical note added. If any revisions are required, please edit the "Technical Notes" field
accordingly. All revisions will be proofread by the Engineering Content Services team.
New Contents:
Prior to this update, the snmpd daemon did not detect errors when accessing the /proc file system. Consequent to this, an attempt to read information about an exited process while gathering information for a HOST-RESOURCES-MIB::hrSWRunTable table caused the daemon to terminate unexpectedly with a segmentation fault. This update adapts the underlying source code to make sure that such errors are now properly detected, and snmpd no longer crashes when populating HOST-RESOURCES-MIB::hrSWRunTable. (BZ#683563).
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHBA-2011-1524.html