Re: libxt_string: fix undefined behavior/incorrect patlen calculation

Re: libxt_string: fix undefined behavior/incorrect patlen calculation

[pud]

(sorry, msg-id lost)

> commit 19b0cd770d1e042c85bf0b278261a61d4cea8193
> Author: Jan Engelhardt <jeng...@medozas.de>
> Date: Thu Feb 12 01:18:35 2009 +0100
...
> - stringinfo->patlen=strlen((char *)&stringinfo->pattern);
> + stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
> +                           sizeof(stringinfo->patlen));

sorry, this doesn't work here, did you mean
sizeof(stringinfo->pattern)?


=;p/ud aka nerdpunk

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gpg-key #C3B04767

Re: libxt_string: fix undefined behavior/incorrect patlen calculation

[Jan Engelhardt]

On Sunday 2009-03-01 23:37, pud wrote:
>(sorry, msg-id lost)
>
>> commit 19b0cd770d1e042c85bf0b278261a61d4cea8193
>> Author: Jan Engelhardt <jeng...@medozas.de>
>> Date: Thu Feb 12 01:18:35 2009 +0100
>...
>> - stringinfo->patlen=strlen((char *)&stringinfo->pattern);
>> + stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
>> +                           sizeof(stringinfo->patlen));
>
>sorry, this doesn't work here, did you mean
>sizeof(stringinfo->pattern)?

What do you mean "doesnot work"?

Re: libxt_string: fix undefined behavior/incorrect patlen calculation

[John Haxby]

Jan Engelhardt wrote:
> On Sunday 2009-03-01 23:37, pud wrote:
>   
>> (sorry, msg-id lost)
>>
>>     
>>> commit 19b0cd770d1e042c85bf0b278261a61d4cea8193
>>> Author: Jan Engelhardt <jeng...@medozas.de>
>>> Date: Thu Feb 12 01:18:35 2009 +0100
>>>       
>> ...
>>     
>>> - stringinfo->patlen=strlen((char *)&stringinfo->pattern);
>>> + stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
>>> +                           sizeof(stringinfo->patlen));
>>>       
>> sorry, this doesn't work here, did you mean
>> sizeof(stringinfo->pattern)?
>>     
>
> What do you mean "doesnot work"?
>   

It looks very weird to me as well.   I may well be confused, but

    stringinfo->patlen = strnlen((char *)&stringinfo->pattern, 
sizeof(stringinfo->patlen))

looks like something roughly equivalent to this:

    char pattern[256];
    int patlen;
    patlen = strlen(pattern, 4);

The "4" is sizeof(int) rather than the size of "pattern"

jch
   

Re: libxt_string: fix undefined behavior/incorrect patlen calculation

[Pablo Neira Ayuso]

[-- Attachment #1: Type: text/plain, Size: 1266 bytes --]

John Haxby wrote:
> Jan Engelhardt wrote:
>> On Sunday 2009-03-01 23:37, pud wrote:
>>  
>>> (sorry, msg-id lost)
>>>
>>>    
>>>> commit 19b0cd770d1e042c85bf0b278261a61d4cea8193
>>>> Author: Jan Engelhardt <jeng...@medozas.de>
>>>> Date: Thu Feb 12 01:18:35 2009 +0100
>>>>       
>>> ...
>>>    
>>>> - stringinfo->patlen=strlen((char *)&stringinfo->pattern);
>>>> + stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
>>>> +                           sizeof(stringinfo->patlen));
>>>>       
>>> sorry, this doesn't work here, did you mean
>>> sizeof(stringinfo->pattern)?
>>>     
>>
>> What do you mean "doesnot work"?
>>   
> 
> It looks very weird to me as well.   I may well be confused, but
> 
>    stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
> sizeof(stringinfo->patlen))
> 
> looks like something roughly equivalent to this:
> 
>    char pattern[256];
>    int patlen;
>    patlen = strlen(pattern, 4);
> 
> The "4" is sizeof(int) rather than the size of "pattern"

Indeed. This was broken in:

http://git.netfilter.org/cgi-bin/gitweb.cgi?p=iptables.git;a=commitdiff;h=37b4bde745698bf140d74e59a2561f34deeb8726;hp=41f03ba382dfd26e7db939fd02447058b1c56f7b

Fix is attached.

-- 
"Los honestos son inadaptados sociales" -- Les Luthiers

[-- Attachment #2: fix-string.patch --]
[-- Type: text/x-diff, Size: 1640 bytes --]

string: fix wrong pattern length calculation

This fixes a problem introduced in 37b4bde745698bf140d74e59a2561f34deeb8726
that leads to the wrong calculation of the pattern length in the
string match.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---

 extensions/libxt_string.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)


diff --git a/extensions/libxt_string.c b/extensions/libxt_string.c
index 5ea529e..ba4b720 100644
--- a/extensions/libxt_string.c
+++ b/extensions/libxt_string.c
@@ -64,9 +64,10 @@ static void string_init(struct xt_entry_match *m)
 static void
 parse_string(const char *s, struct xt_string_info *info)
 {	
+	/* xt_string does not need \0 at the end of the pattern */
 	if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
 		strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
-		info->patlen = strlen(s);
+		info->patlen = strnlen(s, XT_STRING_MAX_PATTERN_SIZE);
 		return;
 	}
 	xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
@@ -75,7 +76,8 @@ parse_string(const char *s, struct xt_string_info *info)
 static void
 parse_algo(const char *s, struct xt_string_info *info)
 {
-	if (strlen(s) <= XT_STRING_MAX_ALGO_NAME_SIZE) {
+	/* xt_string needs \0 for algo name */
+	if (strlen(s) < XT_STRING_MAX_ALGO_NAME_SIZE) {
 		strncpy(info->algo, s, XT_STRING_MAX_ALGO_NAME_SIZE);
 		return;
 	}
@@ -208,8 +210,6 @@ string_parse(int c, char **argv, int invert, unsigned int *flags,
 			else
 				stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
 		}
-		stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
-			sizeof(stringinfo->patlen));
 		*flags |= STRING;
 		break;
 

libxt_string: fix undefined behavior/incorrect patlen calculation

[Jan Engelhardt]

commit 19b0cd770d1e042c85bf0b278261a61d4cea8193
Author: Jan Engelhardt <jengelh@medozas.de>
Date:   Thu Feb 12 01:18:35 2009 +0100

libxt_string: fix undefined behavior/incorrect patlen calculation

strlen ran over the end of the string. Use strnlen to bound it.

Reference: http://bugs.debian.org/513516
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
---
 extensions/libxt_string.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/extensions/libxt_string.c b/extensions/libxt_string.c
index 6bd27c0..aa52fa8 100644
--- a/extensions/libxt_string.c
+++ b/extensions/libxt_string.c
@@ -20,6 +20,7 @@
  *             updated to work with slightly modified
  *             ipt_string_info.
  */
+#define _GNU_SOURCE 1
 #include <stdio.h>
 #include <netdb.h>
 #include <string.h>
@@ -207,7 +208,8 @@ string_parse(int c, char **argv, int invert, unsigned int *flags,
 			else
 				stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
 		}
-		stringinfo->patlen=strlen((char *)&stringinfo->pattern);
+		stringinfo->patlen = strnlen((char *)&stringinfo->pattern,
+			sizeof(stringinfo->patlen));
 		*flags |= STRING;
 		break;
 
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