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Message-ID: <8c6b6666-e5fd-49cd-b357-f491b517d4a3@redhat.com>
Date: Thu, 18 Oct 2018 08:15:04 -0400
From: Prarit Bhargava <prarit@...hat.com>
To: Daniel Thompson <daniel.thompson@...aro.org>
Cc: linux-kernel@...r.kernel.org,
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 10/04/2018 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 ‘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.
>
> 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@...aro.org>
>
>
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.
>
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