Bug 1276032 - Crash on QMP input exceeding limits
Summary: Crash on QMP input exceeding limits
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: qemu-kvm-rhev
Version: 7.0
Hardware: Unspecified
OS: Unspecified
Target Milestone: rc
: ---
Assignee: Markus Armbruster
QA Contact: CongLi
Depends On:
Blocks: 1276036 1288337
TreeView+ depends on / blocked
Reported: 2015-10-28 13:02 UTC by Markus Armbruster
Modified: 2016-11-07 20:51 UTC (History)
7 users (show)

Fixed In Version: qemu-kvm-rhev-2.5.0-1.el7
Doc Type: Bug Fix
Doc Text:
Cause: JSON parser's implementation is ridiculously inefficient, and error handling when nesting exceeds limit is flawed. Consequence: excessive memory use when processing QMP input (~500MiB for a test case with ~100k tokens), crash on input exceeding nesting limit (1024 curly braces or 1024 square brackets, counted separately). Fix: use simpler parsing techniques and data structurs, correct input size limiting. Result: reasonable memory use (test case down to ~20MiB), input exceeding nesting limit (1024 braces + brackets, *not* counted separately) is cleanly rejected.
Clone Of:
: 1276036 (view as bug list)
Last Closed: 2016-11-07 20:51:00 UTC
Target Upstream Version:

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2016:2673 0 normal SHIPPED_LIVE qemu-kvm-rhev bug fix and enhancement update 2016-11-08 01:06:13 UTC

Description Markus Armbruster 2015-10-28 13:02:03 UTC
Description of problem:
The QMP parser attempts to limit nesting depth and input size to
defend against input triggering excessive heap or stack memory use.
However, it crashes when the nesting depth limit is exceeded.  I
suspect it also crashes when the input size is exceeded, but haven't
actually tested.

This is a regression since RHEL-6.

How reproducible:

Steps to Reproduce:
1. Run with a QMP monitor, e.g.
   $ qemu-kvm -nodefaults -S -display none -qmp stdio
2. Input at least 1025 left braces

Actual results:
ERROR:/home/armbru/work/qemu-kvm-rhev7/qobject/json-parser.c:295:parser_context_peek_token: assertion failed: (ctxt->tokens.pos < ctxt->tokens.count)
Aborted (core dumped)

Expected results:
Same behavior as in RHEL-6, i.e.
{"error": {"class": "JSONParsing", "desc": "Invalid JSON syntax", "data": {}}}

Additional info:
It's really the 1025-th left brace.  1024 left braces followed by 1024
right braces doesn't crash.

Broken upstream in commit 65c0f1e "json-parser: don't replicate tokens
at each level of recursion", v1.2.0.

Comment 2 Markus Armbruster 2015-11-20 07:29:31 UTC
Proposed upstream fix:

Related bug: the parser is a ridiculous memory hog.  If we get that fixed upstream together with this bug, I'll widen this bug's scope to cover it.  If not, I'll file a new one.

Comment 3 Markus Armbruster 2015-11-30 08:49:23 UTC
Both the crash and the excessive memory use have been fixed upstream:
df64983 qjson: Limit number of tokens in addition to total size
9bada89 qjson: surprise, allocating 6 QObjects per token is expensive
95385fe qjson: store tokens in a GQueue
d538b25 qjson: Convert to parser to recursive descent
d2ca7c0 qjson: replace QString in JSONLexer with GString
6b9606f qjson: Inline token_is_escape() and simplify
50e2a46 qjson: Inline token_is_keyword() and simplify
c546166 qjson: Give each of the six structural chars its own token type
b8d3b1d qjson: Spell out some silent assumptions
f0ae030 check-qjson: Add test for JSON nesting depth limit
0753113 qjson: Don't crash when input exceeds nesting limit
4f2d31f qjson: Apply nesting limit more sanely

Comment 5 CongLi 2016-08-10 08:26:26 UTC
Reproduce this bug on:

1. Run qemu with a qmp monitor. 
# /usr/libexec/qemu-kvm -nodefaults -S -display none -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 0, "minor": 3, "major": 2}, "package": " (qemu-kvm-rhev-2.3.0-31.el7)"}, "capabilities": []}}

2. Input 1025 left braces.

Qemu aborted with following error.
ERROR:qobject/json-parser.c:295:parser_context_peek_token: assertion failed: (ctxt->tokens.pos < ctxt->tokens.count)
Aborted (core dumped)

Verify this bug on:

1. Run qemu with a qmp monitor.
# /usr/libexec/qemu-kvm -nodefaults -S -display none -qmp stdio{"QMP": {"version": {"qemu": {"micro": 0, "minor": 6, "major": 2}, "package": " (qemu-kvm-rhev-2.6.0-19.el7)"}, "capabilities": []}}

2. Input 1025 left braces.

1. qemu not aborted and there is error in qmp.
{"error": {"class": "GenericError", "desc": "Invalid JSON syntax"}}
2. qemu not crash with 1025 left braces and 1024 right braces,
   got same error as above.

Please be free to correct if there is any problem.


Comment 6 Gu Nini 2016-09-01 02:25:11 UTC
Change the bug status to verified according to comment #5.

Comment 8 errata-xmlrpc 2016-11-07 20:51:00 UTC
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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