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Re: [Qemu-devel] [PATCH 2/8] job: Fix off-by-one accesses to JobSTT and

From: Liam Merwick
Subject: Re: [Qemu-devel] [PATCH 2/8] job: Fix off-by-one accesses to JobSTT and JobVerbTable
Date: Fri, 31 Aug 2018 14:22:04 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 30/08/18 19:34, Eric Blake wrote:
On 08/30/2018 10:47 AM, Liam Merwick wrote:
In the array dereference of JobVerbTable[verb] in job_apply_verb()
the check of the index, verb, allows an overrun because an index
equal to the array size is permitted.

Similarly, in the array dereference of JobSTT[s0][s1] with index s1
in job_state_transition(), an off-by-one overrun is possible.

Fortunately, these are just assertions that are too weak; we don't have any actual callers passing the __MAX entry to cause an actual overrun.

True. In v2 I'll clarify that in the commit message

Signed-off-by: Liam Merwick <address@hidden>
Reviewed-by: Darren Kenny <address@hidden>
Reviewed-by: Mark Kanda <address@hidden>
  job.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Eric Blake <address@hidden>


diff --git a/job.c b/job.c
index e36ebaafd81c..40320566f43b 100644
--- a/job.c
+++ b/job.c
@@ -166,7 +166,7 @@ bool job_is_internal(Job *job)
  static void job_state_transition(Job *job, JobStatus s1)
      JobStatus s0 = job->status;
-    assert(s1 >= 0 && s1 <= JOB_STATUS__MAX);
+    assert(s1 >= 0 && s1 < JOB_STATUS__MAX);
      trace_job_state_transition(job, job->ret,
                                 JobSTT[s0][s1] ? "allowed" : "disallowed",
                                 JobStatus_str(s0), JobStatus_str(s1));
@@ -181,7 +181,7 @@ static void job_state_transition(Job *job, JobStatus s1)
  int job_apply_verb(Job *job, JobVerb verb, Error **errp)
      JobStatus s0 = job->status;
-    assert(verb >= 0 && verb <= JOB_VERB__MAX);
+    assert(verb >= 0 && verb < JOB_VERB__MAX);
      trace_job_apply_verb(job, JobStatus_str(s0), JobVerb_str(verb),
                           JobVerbTable[verb][s0] ? "allowed" : "prohibited");
      if (JobVerbTable[verb][s0]) {

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