Bug 848748 - Malformed xdr request causes reading uninitialize memory and can cause huge memory leaks
Malformed xdr request causes reading uninitialize memory and can cause huge m...
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: glibc (Show other bugs)
Unspecified Linux
unspecified Severity high
: rc
: ---
Assigned To: Patsy Franklin
Arjun Shankar
Depends On: 892777
Blocks: 845283 852661
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Reported: 2012-08-16 06:55 EDT by Honza Horak
Modified: 2016-11-24 10:48 EST (History)
6 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
A defect in the library made it possible for a corrupt NIS request to cause the library to allocate unbounded amounts of memory and eventually crash. The library has been fixed to limit the size of NIS records to at most 16MB and no longer crashes when processing corrupt NIS requests. It is possible that some configurations with very large NIS maps may no longer work if those maps exceed the new NIS record maximum of 16MB.
Story Points: ---
Clone Of:
Last Closed: 2013-11-21 05:39:57 EST
Type: Bug
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
malformed request that can cause huge memory allocations (97 bytes, application/octet-stream)
2012-08-16 07:00 EDT, Honza Horak
no flags Details
proposed patch that uses sane limits while parsing xdr request (1.31 KB, patch)
2012-08-16 07:01 EDT, Honza Horak
no flags Details | Diff

  None (edit)
Description Honza Horak 2012-08-16 06:55:47 EDT
Description of problem:
This issue has been found during analysing of bug #845283.

Let's have NIS client and server configured. glibc's functions like yp_match then send UDP packets to NIS server to ask for network information like login names, passwords etc. Requests are byte strings containing e.g. "...<domainname length><domainname string>...".

When we change length field of the xdr request, while the rest of the string is unchanged and pass such malformed request to the ypserv daemon for example, glibc routine allocates huge memory and then tries to read huge amount of such unallocated memory.

ypserv has a bug #845283, that causes not freeing memory when request is not parsed properly, which results in huge memory leaks and daemon failure. While freeing memory after failed parsing has to be fixed in ypserv, glibc should prevent such behaviour and not allocate more memory than necessary to avoid reading unallocated memory.

There are already limits for NIS fields like domainname, mapname, etc., but they're not used in the parsing functions. Valgrind prints then the following error:

==16566== Conditional jump or move depends on uninitialised value(s)
==16566==    at 0x4A077F9: __GI_strlen (mc_replace_strmem.c:284)
==16566==    by 0x51587F6: xdr_string (xdr.c:680)
==16566==    by 0x4E2D5AD: xdr_ypreq_key (yp_xdr.c:50)
==16566==    by 0x10B092: ypprog_2 (ypserv.c:222)
==16566==    by 0x5156398: svc_getreq_common (svc.c:485)
==16566==    by 0x5155ED0: svc_getreq_poll (svc.c:415)
==16566==    by 0x5156A02: svc_run (svc_run.c:94)
==16566==    by 0x10B84C: main (ypserv.c:726)

Using the following sane limits to NIS fields should prevent such behaviour:
#define YPMAXRECORD 1024
#define YPMAXDOMAIN 64
#define YPMAXMAP 64
#define YPMAXPEER 64

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. start ypserv daemon
2. configure ypbind to use that ypserv daemon
3. create a malformed request string (example of such request will be attached as ypserv-packet-bin)
4. cat ypserv-packet-bin |nc -u 811 ( is where ypserv listens for UDP requests)

Actual results:
huge amount of memory is allocated and then uninitialized memory is read during parsing request

Expected results:
amount of memory allocated during request parsing is limited to a sane amount
Comment 1 Honza Horak 2012-08-16 07:00:30 EDT
Created attachment 604885 [details]
malformed request that can cause huge memory allocations

Use this like this (having ypserv listening for UDP on
cat ypserv-packet-bin |nc -u 788
Comment 2 Honza Horak 2012-08-16 07:01:44 EDT
Created attachment 604886 [details]
proposed patch that uses sane limits while parsing xdr request
Comment 14 Jeff Law 2012-10-01 17:37:28 EDT
Resetting flags for 6.5 consideration.
Comment 16 Jason Montleon 2013-01-08 14:53:34 EST
This approach causes problems with the slapi-nis plugin in IPA.
Comment 18 Carlos O'Donell 2013-02-04 10:57:02 EST
We'll be looking at this issue as part of the review process for the next release. We'll keep the issue updated.
Comment 23 errata-xmlrpc 2013-11-21 05:39:57 EST
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.


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