Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1628268

Re: [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in kprobe_lookup_name()

Show all headers | View raw

Sent too soon.  The suggestions don't guarantee null termination.  Refined, below. (Sorry for the noise.)

On 04/21/2017 08:33 AM, Paul Clarke wrote:
> On 04/21/2017 07:33 AM, Naveen N. Rao wrote:
>> Convert usage of strchr()/strncpy()/strncat() to
>> strnchr()/memcpy()/strlcat() for simpler and safer string manipulation.

>> diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
>> index 97b5eed1f76d..c73fb6e3b43f 100644
>> --- a/arch/powerpc/kernel/kprobes.c
>> +++ b/arch/powerpc/kernel/kprobes.c
>> @@ -65,28 +65,27 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
>>  	char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
>>  	const char *modsym;
>>  	bool dot_appended = false;
>> -	if ((modsym = strchr(name, ':')) != NULL) {
>> +	if ((modsym = strnchr(name, ':', MODULE_NAME_LEN)) != NULL) {
>>  		modsym++;
>>  		if (*modsym != '\0' && *modsym != '.') {
>>  			/* Convert to <module:.symbol> */
>> -			strncpy(dot_name, name, modsym - name);
>> +			memcpy(dot_name, name, modsym - name);
>>  			dot_name[modsym - name] = '.';
>>  			dot_name[modsym - name + 1] = '\0';
>> -			strncat(dot_name, modsym,
>> -				sizeof(dot_name) - (modsym - name) - 2);
>> +			strlcat(dot_name, modsym, sizeof(dot_name));
> 
> Would it be more efficient here to replace this:
> --
> dot_name[modsym - name + 1] = '\0';
> strlcat(dot_name, modsym, sizeof(dot_name));
> --
> 
> with this:
> strncpy(&dot_name[modsym - name + 1], modsym, KSYM_NAME_LEN);

keep the null termination, and just adjust the starting point for strlcat:
--
dot_name[modsym - name + 1] = '\0';
strlcat(&dot_name[modsym - name + 1], modsym, KSYM_NAME_LEN);
--

> (So you aren't rescanning dot_name to find the end, when you already know the end position?)
> 
>>  			dot_appended = true;
>>  		} else {
>>  			dot_name[0] = '\0';
>> -			strncat(dot_name, name, sizeof(dot_name) - 1);
>> +			strlcat(dot_name, name, sizeof(dot_name));
> 
> and here do:
> strncpy(dot_name, name, sizeof(dot_name));
> 
> (and remove the null termination immediately above)

nevermind.  :-)

> 
>>  		}
>>  	} else if (name[0] != '.') {
>>  		dot_name[0] = '.';
>>  		dot_name[1] = '\0';
>> -		strncat(dot_name, name, KSYM_NAME_LEN - 2);
>> +		strlcat(dot_name, name, sizeof(dot_name));
> 
> and here do:
> strncpy(&dot_name[1], name, sizeof(dot_name));
> 
> (and remove the null termination immediately above)
> 

nevermind.  :-)

>>  		dot_appended = true;
>>  	} else {
>>  		dot_name[0] = '\0';
>> -		strncat(dot_name, name, KSYM_NAME_LEN - 1);
>> +		strlcat(dot_name, name, sizeof(dot_name));
> 
> and here do:
> strncpy(dot_name, name, sizeof(dot_name));
> 
> (and remove the null termination immediately above)
> 
>>  	}

nevermind.  :-)

PC

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v3 3/7] kprobes: validate the symbol name length "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-19 15:00 +0200
  Re: [PATCH v3 3/7] kprobes: validate the symbol name length Masami Hiramatsu <mhiramat@kernel.org> - 2017-04-19 17:40 +0200
    Re: [PATCH v3 3/7] kprobes: validate the symbol name length "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-19 18:40 +0200
      Re: [PATCH v3 3/7] kprobes: validate the symbol name length Masami Hiramatsu <mhiramat@kernel.org> - 2017-04-21 15:50 +0200
        Re: [PATCH v3 3/7] kprobes: validate the symbol name length "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-23 17:50 +0200
  Re: [PATCH v3 3/7] kprobes: validate the symbol name length Michael Ellerman <mpe@ellerman.id.au> - 2017-04-20 08:10 +0200
    Re: [PATCH v3 3/7] kprobes: validate the symbol name length "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-20 09:30 +0200
  [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in kprobe_lookup_name() "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-21 14:40 +0200
    Re: [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in  kprobe_lookup_name() Paul Clarke <pc@us.ibm.com> - 2017-04-21 15:40 +0200
      Re: [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in  kprobe_lookup_name() Paul Clarke <pc@us.ibm.com> - 2017-04-21 15:40 +0200
      Re: [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in  kprobe_lookup_name() Paul Clarke <pc@us.ibm.com> - 2017-04-21 16:00 +0200
        Re: [PATCH v4 4/7] powerpc/kprobes: Use safer string functions in  kprobe_lookup_name() "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-23 19:20 +0200
  [PATCH v4 3/7] kprobes: validate the symbol name provided during probe registration "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-21 14:40 +0200
    Re: [PATCH v4 3/7] kprobes: validate the symbol name provided during  probe registration Paul Clarke <pc@us.ibm.com> - 2017-04-21 15:20 +0200
      Re: [PATCH v4 3/7] kprobes: validate the symbol name provided during  probe registration "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-21 15:30 +0200
    Re: [PATCH v4 3/7] kprobes: validate the symbol name provided  during probe registration Masami Hiramatsu <mhiramat@kernel.org> - 2017-04-21 16:00 +0200
    Re: [PATCH v4 3/7] kprobes: validate the symbol name provided during probe registration Michael Ellerman <mpe@ellerman.id.au> - 2017-04-22 08:00 +0200
      Re: [PATCH v4 3/7] kprobes: validate the symbol name provided during  probe registration "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> - 2017-04-23 19:50 +0200

csiph-web