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

[Prarit Bhargava]

On 10/04/2018 08:45 AM, Daniel Thompson wrote:
> On Thu, Oct 04, 2018 at 08:25:30AM -0400, Prarit Bhargava wrote:
>> 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 âkallsyms_symbol_nextâ:
>>>> kernel/debug/kdb/kdb_support.c:239:4: warning: âstrncpyâ specified bound
>>>> depends on the length of the source argument [-Wstringop-overflow=]
>>>> ÂÂÂÂÂ strncpy(prefix_name, name, strlen(name)+1);
>>>> ÂÂÂÂÂ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>> 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@xxxxxxxxxx>
>>>> Cc: Jonathan Toppins <jtoppins@xxxxxxxxxx>
>>>> Cc: Jason Wessel <jason.wessel@xxxxxxxxxxxxx>
>>>> Cc: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
>>>> Cc: kgdb-bugreport@xxxxxxxxxxxxxxxxxxxxx
>>>> ---
>>>> Â kernel/debug/kdb/kdb_io.cÂÂÂÂÂ | 15 +++++++++------
>>>> Â kernel/debug/kdb/kdb_private.h |Â 2 +-
>>>> Â kernel/debug/kdb/kdb_support.c | 10 +++++-----
>>>> Â 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)
>>>> ÂÂÂÂÂ int count;
>>>> ÂÂÂÂÂ int i;
>>>> ÂÂÂÂÂ int diag, dtab_count;
>>>> -ÂÂÂ int key;
>>>> +ÂÂÂ int key, buf_size, ret;
>>>> Â Â ÂÂÂÂÂ diag = kdbgetintenv("DTABCOUNT", &dtab_count);
>>>> @@ -336,9 +336,8 @@ static char *kdb_read(char *buffer, size_t bufsize)
>>>> ÂÂÂÂÂÂÂÂÂ else
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ p_tmp = tmpbuffer;
>>>> ÂÂÂÂÂÂÂÂÂ len = strlen(p_tmp);
>>>> -ÂÂÂÂÂÂÂ count = kallsyms_symbol_complete(p_tmp,
>>>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ sizeof(tmpbuffer) -
>>>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ (p_tmp - tmpbuffer));
>>>> +ÂÂÂÂÂÂÂ buf_size = sizeof(tmpbuffer) - (p_tmp - tmpbuffer);
>>>> +ÂÂÂÂÂÂÂ count = kallsyms_symbol_complete(p_tmp, buf_size);
>>>> ÂÂÂÂÂÂÂÂÂ if (tab == 2 && count > 0) {
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ kdb_printf("\n%d symbols are found.", count);
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ if (count > dtab_count) {
>>>> @@ -350,9 +349,13 @@ static char *kdb_read(char *buffer, size_t bufsize)
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ }
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ kdb_printf("\n");
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ for (i = 0; i < count; i++) {
>>>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (WARN_ON(!kallsyms_symbol_next(p_tmp, i)))
>>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ret = kallsyms_symbol_next(p_tmp, i, buf_size);
>>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ if (WARN_ON(!ret))
>>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 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.
> 
> It's OK. You describe the behaviour I expect but I was misreading the
> code (not realizing that kallsyms_symbol_next() had not become a 0 on
> success success function).
> 
> However after reviewing the code (properly this time) I wonder if the
> WARN_ON() should be improved to match the return value for the function:
> 
>   WARN_ON(ret >= 0 && ret < len)
> 
> That said, checking the symbol length is pretty paranoid and getting
> close to nitpicking so I'll leave it up to you and, with or without, the
> change:
> 
> Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> 
> 

I think we should leave it as is for now.  OOC was this patch picked up by
anyone's repo for staging for 4.20?

P.

> Daniel.
>