From: George Dunlap <george.dunlap@citrix.com>
To: Ian Campbell <ian.campbell@citrix.com>,
George Dunlap <george.dunlap@eu.citrix.com>,
Harmandeep Kaur <write.harmandeep@gmail.com>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Wei Liu <wei.liu2@citrix.com>,
xen-devel <xen-devel@lists.xen.org>
Subject: Re: New Defects reported by Coverity Scan for XenProject
Date: Thu, 25 Feb 2016 10:06:45 +0000 [thread overview]
Message-ID: <56CED235.7000506@citrix.com> (raw)
In-Reply-To: <1456394431.6225.182.camel@citrix.com>
On 25/02/16 10:00, Ian Campbell wrote:
>
> On Wed, 2016-02-24 at 21:02 -0800, scan-admin@coverity.com wrote:
>> Hi,
>>
>> Please find the latest report on new defect(s) introduced to XenProject found with Coverity Scan.
>>
>> 2 new defect(s) introduced to XenProject found with Coverity Scan.
>> 12 defect(s), reported by Coverity Scan earlier, were marked fixed in the recent build analyzed by Coverity Scan.
>>
>> New defect(s) Reported-by: Coverity Scan
>> Showing 2 of 2 defect(s)
>>
>>
>> ** CID 1354244: Null pointer dereferences (FORWARD_NULL)
>> /tools/libxc/xc_tbuf.c: 72 in xc_tbuf_get_size()
>>
>>
>> ________________________________________________________________________________________________________
>> *** CID 1354244: Null pointer dereferences (FORWARD_NULL)
>> /tools/libxc/xc_tbuf.c: 72 in xc_tbuf_get_size()
>> 66 return rc;
>> 67
>> 68 t_info = xc_map_foreign_range(xch, DOMID_XEN,
>> 69 sysctl.u.tbuf_op.size, PROT_READ | PROT_WRITE,
>> 70 sysctl.u.tbuf_op.buffer_mfn);
>> 71
>>>>> CID 1354244: Null pointer dereferences (FORWARD_NULL)
>>>>> Comparing "t_info" to null implies that "t_info" might be null.
>> 72 if ( t_info == NULL || t_info->tbuf_size == 0 )
>> 73 rc = -1;
>> 74 else
>> 75 *size = t_info->tbuf_size;
>> 76
>> 77 xenforeignmemory_unmap(xch->fmem, t_info, sysctl.u.tbuf_op.size);
>
> This is complaining about the eventual munmap(t_info) => munmap(NULL) which
> is behind xenforeignmemory_unmap().
>
> Looks like it was newly added by the fix to CID 1351228 in 7c479883b04a
> ("libxc: fix leak of t_info in xc_tbuf_get_size()").
> xenforeignmemory_unmap() should behave like munmap WRT tollerance of NULL,
> I'm not 100% sure what that behaviour is since 0 is a valid address.
> xenforeignmemory.h no doubt wants updating with the desired semantics and
> either this code of the implementation adjusting to match.
>
> While here I notice that using xc_map_*() to create the mapping and
> xenforeignmemory_unmap() to destroy it is a bit odd since they are strictly
> two separate APIs, even if one happens to be implemented in terms of the
> other. Being libxc internal this code is at liberty to use xc_map_* but
> should then use plain munmap to undo it, or it would also be reasonable to
> port this code fully to the xenforeignmemory interface.
>
>>
>> ** CID 1354243: Control flow issues (DEADCODE)
>> /tools/xentrace/xenalyze.c: 4148 in cr3_dump_list()
>>
>>
>> ________________________________________________________________________________________________________
>> *** CID 1354243: Control flow issues (DEADCODE)
>> /tools/xentrace/xenalyze.c: 4148 in cr3_dump_list()
>> 4142
>> 4143 /* Count the number of elements */
>> 4144 for(p=head; p; p=p->next)
>> 4145 N++;
>> 4146
>> 4147 if(!N)
>>>>> CID 1354243: Control flow issues (DEADCODE)
>>>>> Execution cannot reach this statement: "return;".
>
> Here it has observed that due to the (above, just out of the context given
> here) "if (!head) return" that the for loop must run at least once, so N
> cannot be 0.
>
> My guess is that this is a prexisting issue which was exposed to coverities
> beady eye somehow by 28ab9f3d0e7c ("tools/xenalyze: Fix build with clang").
> Or maybe this was previous marked deliberate but the change has caused
> coverity to think this is a different instance of the same thing, eitherway
> I don't think the issue itself is new.
>
> FWIW having both if (!head) return and if (!N) return looks redundant to
> me, the other two similar looking instances (from grepping for N++) have
> only the latter check.
Yes, they're certainly redundant, and I definitely prefer the latter
check rather than the former. I'll send a patch.
-George
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next prev parent reply other threads:[~2016-02-25 10:06 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <56ce8ad13abd2_bd9abd33094410@ss1435.mail>
2016-02-25 10:00 ` New Defects reported by Coverity Scan for XenProject Ian Campbell
2016-02-25 10:06 ` George Dunlap [this message]
[not found] <664dc165759df_5e9362b92d249399c762@prd-scan-dashboard-0.mail>
2024-05-22 10:05 ` Jan Beulich
2024-05-22 13:49 ` Andrew Cooper
[not found] <6637576caf98c_10d9e42c57d37559ac60499@prd-scan-dashboard-0.mail>
2024-05-06 7:46 ` Jan Beulich
[not found] <6547674e54da3_1c3af2c62521719a8359bc@prd-scan-dashboard-0.mail>
2023-11-06 7:36 ` Jan Beulich
[not found] <64859cf3a1e46_712752abb10eab98834b9@prd-scan-dashboard-0.mail>
2023-06-12 10:54 ` Jan Beulich
2023-06-12 11:06 ` Andrew Cooper
[not found] <600d4d7f99bc3_241662b17c874cf6097f1@prd-scan-dashboard-0.mail>
2021-01-25 10:14 ` Jan Beulich
[not found] <5700f7b3e7d5c_3fdf4db3186252@ss1435.mail>
2016-04-04 15:07 ` Ian Jackson
[not found] <551be9e0474d8_2970d1331454394@scan.coverity.com.mail>
2015-04-02 14:32 ` Ian Campbell
2015-04-02 15:43 ` Charles Arnold
[not found] <E1Vgaam-0000UH-GS@build-l3.scan.coverity.com>
2013-11-13 13:51 ` Ian Campbell
2013-11-13 14:01 ` David Vrabel
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