linux-kernel - Re: [PATCH v2] kdb: Use strscpy with destination buffer size

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Date:   Thu, 4 Oct 2018 08:25:30 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>,
        linux-kernel@...r.kernel.org
Cc:     Jonathan Toppins <jtoppins@...hat.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net
Subject: Re: [PATCH v2] kdb: Use strscpy with destination buffer size



On 10/02/2018 11:53 AM, Daniel Thompson wrote:
> On 20/09/2018 13:59, Prarit Bhargava wrote:
>> gcc 8.1.0 warns with:
>>
>> kernel/debug/kdb/kdb_support.c: In function ‘kallsyms_symbol_next’:
>> kernel/debug/kdb/kdb_support.c:239:4: warning: ‘strncpy’ specified bound
>> depends on the length of the source argument [-Wstringop-overflow=]
>>       strncpy(prefix_name, name, strlen(name)+1);
>>       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> kernel/debug/kdb/kdb_support.c:239:31: note: length computed here
>>
>> Use strscpy() with the destination buffer size, and use ellipses when
>> displaying truncated symbols.
>>
>> v2: Use strscpy()
>>
>> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
>> Cc: Jonathan Toppins <jtoppins@...hat.com>
>> Cc: Jason Wessel <jason.wessel@...driver.com>
>> Cc: Daniel Thompson <daniel.thompson@...aro.org>
>> Cc: kgdb-bugreport@...ts.sourceforge.net
>> ---
>>   kernel/debug/kdb/kdb_io.c      | 15 +++++++++------
>>   kernel/debug/kdb/kdb_private.h |  2 +-
>>   kernel/debug/kdb/kdb_support.c | 10 +++++-----
>>   3 files changed, 15 insertions(+), 12 deletions(-)
>>
>> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
>> index ed5d34925ad0..6a4b41484afe 100644
>> --- a/kernel/debug/kdb/kdb_io.c
>> +++ b/kernel/debug/kdb/kdb_io.c
>> @@ -216,7 +216,7 @@ static char *kdb_read(char *buffer, size_t bufsize)
>>       int count;
>>       int i;
>>       int diag, dtab_count;
>> -    int key;
>> +    int key, buf_size, ret;
>>           diag = kdbgetintenv("DTABCOUNT", &dtab_count);
>> @@ -336,9 +336,8 @@ static char *kdb_read(char *buffer, size_t bufsize)
>>           else
>>               p_tmp = tmpbuffer;
>>           len = strlen(p_tmp);
>> -        count = kallsyms_symbol_complete(p_tmp,
>> -                         sizeof(tmpbuffer) -
>> -                         (p_tmp - tmpbuffer));
>> +        buf_size = sizeof(tmpbuffer) - (p_tmp - tmpbuffer);
>> +        count = kallsyms_symbol_complete(p_tmp, buf_size);
>>           if (tab == 2 && count > 0) {
>>               kdb_printf("\n%d symbols are found.", count);
>>               if (count > dtab_count) {
>> @@ -350,9 +349,13 @@ static char *kdb_read(char *buffer, size_t bufsize)
>>               }
>>               kdb_printf("\n");
>>               for (i = 0; i < count; i++) {
>> -                if (WARN_ON(!kallsyms_symbol_next(p_tmp, i)))
>> +                ret = kallsyms_symbol_next(p_tmp, i, buf_size);
>> +                if (WARN_ON(!ret))
>>                       break;
> I'm getting confused by having two different branches on ret.
> 
> Don't get a WARN_ON() when ret == -E2BIG?
> 
> 

Should we WARN on a really long symbol?  I don't think we should as we're
handling that by truncating the output and adding ellipses below.

P.

> Daniel.
> 
> 
>> -                kdb_printf("%s ", p_tmp);
>> +                if (ret != -E2BIG)
>> +                    kdb_printf("%s ", p_tmp);
>> +                else
>> +                    kdb_printf("%s... ", p_tmp);
>>                   *(p_tmp + len) = '\0';
>>               }
>>               if (i >= dtab_count)