From: Jakob Koschel <jakobkoschel@gmail.com>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Andrew Lunn <andrew@lunn.ch>,
Vivien Didelot <vivien.didelot@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
Lars Povlsen <lars.povlsen@microchip.com>,
Steen Hegelund <Steen.Hegelund@microchip.com>,
UNGLinuxDriver@microchip.com, Ariel Elior <aelior@marvell.com>,
Manish Chopra <manishc@marvell.com>,
Edward Cree <ecree.xilinx@gmail.com>,
Martin Habets <habetsm.xilinx@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>, Jiri Pirko <jiri@resnulli.us>,
Casper Andersson <casper.casan@gmail.com>,
Bjarni Jonasson <bjarni.jonasson@microchip.com>,
Colin Ian King <colin.king@intel.com>,
Michael Walle <michael@walle.cc>,
Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
Arnd Bergmann <arnd@arndb.de>, Eric Dumazet <edumazet@google.com>,
Di Zhu <zhudi21@huawei.com>, Xu Wang <vulab@iscas.ac.cn>,
Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Mike Rapoport <rppt@kernel.org>,
Brian Johannesmeyer <bjohannesmeyer@gmail.com>,
Cristiano Giuffrida <c.giuffrida@vu.nl>,
"Bos, H.J." <h.j.bos@vu.nl>
Subject: Re: [PATCH net-next 03/15] net: dsa: mv88e6xxx: Replace usage of found with dedicated iterator
Date: Sat, 9 Apr 2022 01:44:00 +0200 [thread overview]
Message-ID: <C2AFC0FB-08EC-4421-AF44-8C485BF48879@gmail.com> (raw)
In-Reply-To: <20220408123101.p33jpynhqo67hebe@skbuf>
Hi Vladimir,
> On 8. Apr 2022, at 14:31, Vladimir Oltean <olteanv@gmail.com> wrote:
>
> Hi Jakob,
>
> On Thu, Apr 07, 2022 at 12:28:48PM +0200, Jakob Koschel wrote:
>> To move the list iterator variable into the list_for_each_entry_*()
>> macro in the future it should be avoided to use the list iterator
>> variable after the loop body.
>>
>> To *never* use the list iterator variable after the loop it was
>> concluded to use a separate iterator variable instead of a
>> found boolean [1].
>>
>> This removes the need to use a found variable and simply checking if
>> the variable was set, can determine if the break/goto was hit.
>>
>> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
>> Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
>> ---
>> drivers/net/dsa/mv88e6xxx/chip.c | 21 ++++++++++-----------
>> 1 file changed, 10 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
>> index 64f4fdd02902..f254f537c357 100644
>> --- a/drivers/net/dsa/mv88e6xxx/chip.c
>> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
>> @@ -1381,28 +1381,27 @@ static int mv88e6xxx_set_mac_eee(struct dsa_switch *ds, int port,
>> /* Mask of the local ports allowed to receive frames from a given fabric port */
>> static u16 mv88e6xxx_port_vlan(struct mv88e6xxx_chip *chip, int dev, int port)
>> {
>> + struct dsa_port *dp = NULL, *iter, *other_dp;
>> struct dsa_switch *ds = chip->ds;
>> struct dsa_switch_tree *dst = ds->dst;
>> - struct dsa_port *dp, *other_dp;
>> - bool found = false;
>> u16 pvlan;
>>
>> /* dev is a physical switch */
>> if (dev <= dst->last_switch) {
>> - list_for_each_entry(dp, &dst->ports, list) {
>> - if (dp->ds->index == dev && dp->index == port) {
>> - /* dp might be a DSA link or a user port, so it
>> + list_for_each_entry(iter, &dst->ports, list) {
>> + if (iter->ds->index == dev && iter->index == port) {
>> + /* iter might be a DSA link or a user port, so it
>> * might or might not have a bridge.
>> - * Use the "found" variable for both cases.
>> + * Set the "dp" variable for both cases.
>> */
>> - found = true;
>> + dp = iter;
>> break;
>> }
>> }
>> /* dev is a virtual bridge */
>> } else {
>> - list_for_each_entry(dp, &dst->ports, list) {
>> - unsigned int bridge_num = dsa_port_bridge_num_get(dp);
>> + list_for_each_entry(iter, &dst->ports, list) {
>> + unsigned int bridge_num = dsa_port_bridge_num_get(iter);
>>
>> if (!bridge_num)
>> continue;
>> @@ -1410,13 +1409,13 @@ static u16 mv88e6xxx_port_vlan(struct mv88e6xxx_chip *chip, int dev, int port)
>> if (bridge_num + dst->last_switch != dev)
>> continue;
>>
>> - found = true;
>> + dp = iter;
>> break;
>> }
>> }
>>
>> /* Prevent frames from unknown switch or virtual bridge */
>> - if (!found)
>> + if (!dp)
>> return 0;
>>
>> /* Frames from DSA links and CPU ports can egress any local port */
>> --
>> 2.25.1
>>
>
> Let's try to not make convoluted code worse. Do the following 2 patches
> achieve what you are looking for? Originally I had a single patch (what
> is now 2/2) but I figured it would be cleaner to break out the unrelated
> change into what is now 1/2.
I do agree with not making convoluted code worse, but I was reluctant with
e.g. introducing new functions for this because others essentially
have the opposite opinion on this.
I however like solving it that way, it makes it a lot cleaner.
>
> If you want I can submit these changes separately.
Sure if you want to submit them separately, go ahead. Otherwise I can
integrate it into a v2, whatever you prefer essentially.
>
> -----------------------------[ cut here ]-----------------------------
> From 2d84ecd87566b1535a04526b4ebb2764e764625f Mon Sep 17 00:00:00 2001
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> Date: Fri, 8 Apr 2022 15:15:30 +0300
> Subject: [PATCH 1/2] net: dsa: mv88e6xxx: remove redundant check in
> mv88e6xxx_port_vlan()
>
> We know that "dev > dst->last_switch" in the "else" block.
> In other words, that "dev - dst->last_switch" is > 0.
>
> dsa_port_bridge_num_get(dp) can be 0, but the check
> "if (bridge_num + dst->last_switch != dev) continue", rewritten as
> "if (bridge_num != dev - dst->last_switch) continue", aka
> "if (bridge_num != something which cannot be 0) continue",
> makes it redundant to have the extra "if (!bridge_num) continue" logic,
> since a bridge_num of zero would have been skipped anyway.
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
> drivers/net/dsa/mv88e6xxx/chip.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index 64f4fdd02902..b3aa0e5bc842 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -1404,9 +1404,6 @@ static u16 mv88e6xxx_port_vlan(struct mv88e6xxx_chip *chip, int dev, int port)
> list_for_each_entry(dp, &dst->ports, list) {
> unsigned int bridge_num = dsa_port_bridge_num_get(dp);
>
> - if (!bridge_num)
> - continue;
> -
> if (bridge_num + dst->last_switch != dev)
> continue;
>
> -----------------------------[ cut here ]-----------------------------
>
> -----------------------------[ cut here ]-----------------------------
> From dabafdbe38b408f7c563ad91fc6e57791055fed7 Mon Sep 17 00:00:00 2001
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> Date: Fri, 8 Apr 2022 14:57:45 +0300
> Subject: [PATCH 2/2] net: dsa: mv88e6xxx: refactor mv88e6xxx_port_vlan()
>
> To avoid bugs and speculative execution exploits due to type-confused
> pointers at the end of a list_for_each_entry() loop, one measure is to
> restrict code to not use the iterator variable outside the loop block.
>
> In the case of mv88e6xxx_port_vlan(), this isn't a problem, as we never
> let the loops exit through "natural causes" anyway, by using a "found"
> variable and then using the last "dp" iterator prior to the break, which
> is a safe thing to do.
>
> Nonetheless, with the expected new syntax, this pattern will no longer
> be possible.
>
> Profit off of the occasion and break the two port finding methods into
> smaller sub-functions. Somehow, returning a copy of the iterator pointer
> is still accepted.
>
> This change makes it redundant to have a "bool found", since the "dp"
> from mv88e6xxx_port_vlan() now holds NULL if we haven't found what we
> were looking for.
>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
> drivers/net/dsa/mv88e6xxx/chip.c | 54 ++++++++++++++++++--------------
> 1 file changed, 31 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> index b3aa0e5bc842..1f35e89053e6 100644
> --- a/drivers/net/dsa/mv88e6xxx/chip.c
> +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> @@ -1378,42 +1378,50 @@ static int mv88e6xxx_set_mac_eee(struct dsa_switch *ds, int port,
> return 0;
> }
>
> +static struct dsa_port *mv88e6xxx_find_port(struct dsa_switch_tree *dst,
> + int sw_index, int port)
> +{
> + struct dsa_port *dp;
> +
> + list_for_each_entry(dp, &dst->ports, list)
> + if (dp->ds->index == sw_index && dp->index == port)
> + return dp;
> +
> + return NULL;
> +}
> +
> +static struct dsa_port *
> +mv88e6xxx_find_port_by_bridge_num(struct dsa_switch_tree *dst,
> + unsigned int bridge_num)
> +{
> + struct dsa_port *dp;
> +
> + list_for_each_entry(dp, &dst->ports, list)
> + if (dsa_port_bridge_num_get(dp) == bridge_num)
> + return dp;
> +
> + return NULL;
> +}
> +
> /* Mask of the local ports allowed to receive frames from a given fabric port */
> static u16 mv88e6xxx_port_vlan(struct mv88e6xxx_chip *chip, int dev, int port)
> {
> struct dsa_switch *ds = chip->ds;
> struct dsa_switch_tree *dst = ds->dst;
> struct dsa_port *dp, *other_dp;
> - bool found = false;
> u16 pvlan;
>
> - /* dev is a physical switch */
> if (dev <= dst->last_switch) {
> - list_for_each_entry(dp, &dst->ports, list) {
> - if (dp->ds->index == dev && dp->index == port) {
> - /* dp might be a DSA link or a user port, so it
> - * might or might not have a bridge.
> - * Use the "found" variable for both cases.
> - */
> - found = true;
> - break;
> - }
> - }
> - /* dev is a virtual bridge */
> + /* dev is a physical switch */
> + dp = mv88e6xxx_find_port(dst, dev, port);
> } else {
> - list_for_each_entry(dp, &dst->ports, list) {
> - unsigned int bridge_num = dsa_port_bridge_num_get(dp);
> -
> - if (bridge_num + dst->last_switch != dev)
> - continue;
> -
> - found = true;
> - break;
> - }
> + /* dev is a virtual bridge */
> + dp = mv88e6xxx_find_port_by_bridge_num(dst,
> + dev - dst->last_switch);
> }
>
> /* Prevent frames from unknown switch or virtual bridge */
> - if (!found)
> + if (!dp)
> return 0;
>
> /* Frames from DSA links and CPU ports can egress any local port */
> -----------------------------[ cut here ]-----------------------------
Thanks,
Jakob
next prev parent reply other threads:[~2022-04-08 23:44 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-07 10:28 [PATCH net-next 00/15] net: Remove use of list iterator after loop body Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 01/15] connector: Replace usage of found with dedicated list iterator variable Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 02/15] net: dsa: sja1105: Remove usage of iterator for list_add() after loop Jakob Koschel
2022-04-08 3:54 ` Jakub Kicinski
2022-04-08 23:58 ` Jakob Koschel
2022-04-09 0:04 ` Jakub Kicinski
2022-04-09 0:08 ` Vladimir Oltean
2022-04-08 7:47 ` Christophe Leroy
2022-04-08 23:49 ` Jakob Koschel
2022-04-08 11:41 ` Vladimir Oltean
2022-04-08 23:54 ` Jakob Koschel
2022-04-10 10:51 ` Jakob Koschel
2022-04-10 11:05 ` Vladimir Oltean
2022-04-10 12:39 ` Jakob Koschel
2022-04-10 18:24 ` Jakob Koschel
2022-04-10 20:02 ` Vladimir Oltean
2022-04-10 20:30 ` Jakob Koschel
2022-04-10 20:34 ` Vladimir Oltean
2022-04-07 10:28 ` [PATCH net-next 03/15] net: dsa: mv88e6xxx: Replace usage of found with dedicated iterator Jakob Koschel
2022-04-08 12:31 ` Vladimir Oltean
2022-04-08 23:44 ` Jakob Koschel [this message]
2022-04-08 23:50 ` Vladimir Oltean
2022-04-09 0:00 ` Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 04/15] net: dsa: Replace usage of found with dedicated list iterator variable Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 05/15] net: sparx5: " Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 06/15] qed: Use " Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 07/15] qed: Replace usage of found with " Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 08/15] qed: Remove usage of list iterator variable after the loop Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 09/15] net: qede: Replace usage of found with dedicated list iterator variable Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 10/15] net: qede: Remove check of list iterator against head past the loop body Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 11/15] sfc: Remove usage of list iterator for list_add() after " Jakob Koschel
2022-04-07 17:42 ` Edward Cree
2022-04-09 0:10 ` Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 12/15] net: netcp: Remove usage of list iterator for list_add() after " Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 13/15] ps3_gelic: Replace usage of found with dedicated list iterator variable Jakob Koschel
2022-04-07 10:28 ` [PATCH net-next 14/15] ipvlan: Remove usage of list iterator variable for the loop body Jakob Koschel
2022-04-07 10:29 ` [PATCH net-next 15/15] team: Remove use of list iterator variable for list_for_each_entry_from() Jakob Koschel
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