From: Matan Azrad <matan@mellanox.com>
To: "Gaëtan Rivet" <gaetan.rivet@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>, Ori Kam <orika@mellanox.com>,
"stable@dpdk.org" <stable@dpdk.org>
Subject: Re: [dpdk-stable] [PATCH] net/failsafe: fix parameters parsing
Date: Thu, 17 Aug 2017 18:52:48 +0000 [thread overview]
Message-ID: <DB6PR0502MB30488298FA30A2DF5E9EDD0CD2830@DB6PR0502MB3048.eurprd05.prod.outlook.com> (raw)
In-Reply-To: <20170817162458.GQ8124@bidouze.vm.6wind.com>
Hi Gaetan
> -----Original Message-----
> From: Gaëtan Rivet [mailto:gaetan.rivet@6wind.com]
> Sent: Thursday, August 17, 2017 7:25 PM
> To: Matan Azrad <matan@mellanox.com>
> Cc: dev@dpdk.org; Ori Kam <orika@mellanox.com>; stable@dpdk.org
> Subject: Re: [PATCH] net/failsafe: fix parameters parsing
>
> On Thu, Aug 17, 2017 at 03:54:23PM +0000, Matan Azrad wrote:
> >
> >
> > > -----Original Message-----
> > > From: Gaëtan Rivet [mailto:gaetan.rivet@6wind.com]
> > > Sent: Thursday, August 17, 2017 6:26 PM
> > > To: Matan Azrad <matan@mellanox.com>
> > > Cc: dev@dpdk.org; Ori Kam <orika@mellanox.com>; stable@dpdk.org
> > > Subject: Re: [PATCH] net/failsafe: fix parameters parsing
> > >
> > > Hi Matan,
> > >
> > > Thanks for spotting the bug.
> > >
> > > On Thu, Aug 17, 2017 at 05:19:41PM +0300, Matan Azrad wrote:
> > > > The corrupted code used wrongly snprintf return value as the
> > > > number of characters actually copied, in spite of the meanning is
> > > > the number of characters which would be generated for the given
> input.
> > > >
> > > > It caused to remain zerod bytes between the failsafe command line
> > > > non sub device parameters indicates end of string.
> > > >
> > > > Hence, when rte_kvargs_parse tried to parse all parameters, it got
> > > > end of string after the first one and the others weren't parsed.
> > > >
> > > > So, if the mac parameters was the first in command line it was
> > > > taken while hotplug_poll was left default, and vice versa.
> > > >
> > > > The fix updates the buffer index by dedicated variable contains
> > > > the copy size, by the way uses memcpy instead of snprintf which is
> > > > good enouth for this copy scenario.
> > >
> > > Actually snprintf should still be used.
> > >
> > Why?
> > We just want to copy from buffer to buffer, no needs snprintf
> > overheads If actually we are not using complicated format.
> >
>
> snprintf plays nice with strings and ensure that it will be terminated by a '\0'.
> It is generally preferable, particularly considering that the parameter string
> we are building here is meant to be parsed by another lib (rte_kvargs).
>
In this specific scenario it is not needed because we for sure know that the length doesn't pass after '\0'.
By using memcpy we can prevent format parsing and other checks done by snprintf.
> > > >
> > > > Fixes: a46f8d584eb8 ("net/failsafe: add fail-safe PMD")
> > > > Cc: stable@dpdk.org
> > > >
> > > > Signed-off-by: Matan Azrad <matan@mellanox.com>
> > > > ---
> > > > drivers/net/failsafe/failsafe_args.c | 14 ++++++++------
> > > > 1 file changed, 8 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/drivers/net/failsafe/failsafe_args.c
> > > > b/drivers/net/failsafe/failsafe_args.c
> > > > index 1f22416..0a98b04 100644
> > > > --- a/drivers/net/failsafe/failsafe_args.c
> > > > +++ b/drivers/net/failsafe/failsafe_args.c
> > > > @@ -271,7 +271,7 @@ static int
> > > > fs_remove_sub_devices_definition(char params[DEVARGS_MAXLEN])
> {
> > > > char buffer[DEVARGS_MAXLEN] = {0};
> > > > - size_t a, b;
> > > > + size_t a, b, temp;
> > >
> > > temp is not descriptive enough.
> >
> > What are about a, b, i ?
> >
> > > You are declaring this variable here because you want to re-use it
> > > instead of `start`. This is an overreach however, this fix must be
> > > restricted to the actual bug.
> >
> > temp is helping to address the original bug, don't we want to reuse
> > variable Instead of 2 if statement variables, maybe other name for all?
> >
>
> The compiler should be able to see that their use does not overlap.
>
This is new for me, thanks for the lesson.
I will update it to len & start as you suggested.
> The issue is that temp is meant to describe a length limit in one branch and
> be a marker of a starting point in another. Thus both variable should be
> named differently to make the intent clear.
>
> When declaring temp (or saved_val) in the higher-scope, you are thus forced
> to use generic, non-descriptive name precisely because you are sharing the
> variable between two different uses.
>
> > Something like:
> > a=> start
> > b=> end
> > i => next
> > temp=> saved_val
> >
> >
You didn't answer what are about my suggestions for new names instead of
a,b and I which are not descriptive too (like temp :))
> > >
> > > > int i;
> > > >
> > > > a = 0;
> > > > @@ -286,12 +286,14 @@ fs_remove_sub_devices_definition(char
> > > params[DEVARGS_MAXLEN])
> > > > ERROR("Invalid parameter");
> > > > return -EINVAL;
> > > > }
> > > > - if (params[b] == ',' || params[b] == '\0')
> > >
> > > Declare the temporary variable in this scope, with a descriptive
> > > name such as "len", "length", "param_len" or something close.
> > >
> > > > - i += snprintf(&buffer[i], b - a + 1, "%s", ¶ms[a]);
> > > > - if (params[b] == '(') {
> > > > - size_t start = b;
> > > > + if (params[b] == ',' || params[b] == '\0') {
> > > > + temp = b - a + 1;
> > >
> > > The value here should be "b - a".
> > > If a != 0 however, then we are parsing a new parameter and buffer
> > > already contains at least one. A comma should be added to separate the
> two.
> > >
> > > An example might clarify what I mean:
> > >
> > > if (params[b] == ',' || params[b] == '\0') {
> > > size_t param_len = b - a;
> > >
> > > if (a)
> > > param_len += 1;
> > > snprintf(&buffer[i], param_len + 1, "%s%s",
> > > a ? "," : "", ¶ms[a]);
> > > i += param_len;
> > > }
> > >
> > > The conditionals about `a` are ugly however, if you find a better
> > > way to write those you are most welcome :).
> > >
> > > > + memcpy(&buffer[i], ¶ms[a], temp);
> > > > + i += temp;
> > > > + } else if (params[b] == '(') {
> > > > + temp = b;
> > > > b += closing_paren(¶ms[b]);
> > > > - if (b == start)
> > >
> >
> > I think the last comma is harmless for next parse But I can just
> > change the last coma to '\0' in the end of function(if exists).
> > But, This solves another issue, don't it? Maybe in different patch?
> >
>
> It might be harmless, but I prefer having a clean output.
> Which other issue? Handling the commas seems in line with properly copying
> regular parameters.
Yes, but it is another issue in this specific copy (don't refer to snprintf return value)
But, it's OK, I think them both can be handle by this patch :)
>
> You could certainly check for the presence of a comma, but you already see
> how ugly the code flow would be ("if it exists"), and you will keep a dirty
> string between two loops, with possibly other branches wanting to return on
> error.
>
> I prefer having a compact, self-contained logic addressing kvargs which
> should not leak conceptual gotcha that the next programmer would need to
> be wary of when trying to touch the code in other parts of the function.
>
If we leave always b-a+1 we potentially can get the next buffer strings:
p1,p2...pN,
or
p1,p2,pN(\0)
while i is the index of the character after a comma or '\0'
so, for prevent the last comma we can override always in the end of function(not between 2 loops) '\0' like this:
if (i >0 )
/* For prevent last comma. */
buffer[i-1] = '\0';
instead of using 2 conditions per non sub device param - 'if(a)' and 'a ? "," : ""'
I think each future programmer can easily understand it.
> > > The changes should be limited to the actual bug. No need to change this.
> > >
> > > > + if (b == temp)
> > > > return -EINVAL;
> > > > b += 1;
> > > > if (params[b] == '\0')
> > > > --
> > > > 2.7.4
> > > >
> > >
> > > Thanks again for the debug and sorry for being nitpicky.
> > >
> > > --
> > > Gaëtan Rivet
> > > 6WIND
> >
> > Regards,
> > Matan Azrad.
>
> --
> Gaëtan Rivet
> 6WIND
Regards
Matan Azrad.
next prev parent reply other threads:[~2017-08-17 18:52 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-17 14:19 Matan Azrad
2017-08-17 15:25 ` Gaëtan Rivet
2017-08-17 15:54 ` Matan Azrad
2017-08-17 16:24 ` Gaëtan Rivet
2017-08-17 18:52 ` Matan Azrad [this message]
2017-08-18 9:03 ` Gaëtan Rivet
2017-08-19 21:24 ` Matan Azrad
2017-08-19 22:07 ` [dpdk-stable] [PATCH v2] " Matan Azrad
2017-08-21 9:34 ` Gaëtan Rivet
2017-08-21 12:02 ` Matan Azrad
2017-08-21 13:25 ` Gaëtan Rivet
2017-08-27 7:23 ` [dpdk-stable] [PATCH v3] " Matan Azrad
2017-08-28 7:52 ` Gaëtan Rivet
2017-08-29 17:05 ` Ferruh Yigit
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