[PATCH net-next] net: phylink: fix NULL pl->pcs dereference during phylink_pcs_poll_start

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/phy/phylink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 1a7550f5fdf5..48f0b9b39491 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c

@@ -766,7 +766,7 @@ static void phylink_pcs_poll_stop(struct phylink *pl)
 
 static void phylink_pcs_poll_start(struct phylink *pl)
 {
-	if (pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
+	if (pl->pcs && pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
 		mod_timer(&pl->link_poll, jiffies + HZ);
 }
 

-- 
2.25.1

On Wed, Jun 29, 2022 at 10:33:58PM +0300, Vladimir Oltean wrote:

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Thanks.

Reviewed-by: Russell King (Oracle) <redacted>

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On 29.06.22 21:42, Russell King (Oracle) wrote:

On Wed, Jun 29, 2022 at 10:33:58PM +0300, Vladimir Oltean wrote:

quoted

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Thanks.

Reviewed-by: Russell King (Oracle) <redacted>

Fixes the problem on my side.

Tested-by: Gerhard Engleder <redacted>

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Tested-by: Michael Walle <redacted> # on kontron-kbox-a-230-ls

-michael

Vladimir, Russell,

On 29/06/2022 at 21:33, Vladimir Oltean wrote:

Fixes the NULL pointer on my boards:
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sam9x60ek

Best regards,
   Nicolas


-- 
Nicolas Ferre

On Thu, Jun 30, 2022 at 03:46:54PM +0200, Nicolas Ferre wrote:

Vladimir, Russell,

On 29/06/2022 at 21:33, Vladimir Oltean wrote:

quoted

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

Fixes: bfac8c490d60 ("net: phylink: disable PCS polling over major configuration")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
  drivers/net/phy/phylink.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 1a7550f5fdf5..48f0b9b39491 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c

@@ -766,7 +766,7 @@ static void phylink_pcs_poll_stop(struct phylink *pl)
  static void phylink_pcs_poll_start(struct phylink *pl)
  {
-	if (pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
+	if (pl->pcs && pl->pcs->poll && pl->cfg_link_an_mode == MLO_AN_INBAND)
  		mod_timer(&pl->link_poll, jiffies + HZ);
  }

Fixes the NULL pointer on my boards:
Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com> # on sam9x60ek

Thanks all, hopefully it'll get applied to net-next soon.

Sadly, this slipped through my testing, as the only platform I have
access to at the moment always supplies a PCS (mvneta based) so there's
no way my testing would ever have caught this. Sorry for the problems.

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Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski [off-list ref]:

On Wed, 29 Jun 2022 22:33:58 +0300 you wrote:

The current link mode of the phylink instance may not require an
attached PCS. However, phylink_major_config() unconditionally
dereferences this potentially NULL pointer when restarting the link poll
timer, which will panic the kernel.

Fix the problem by checking whether a PCS exists in phylink_pcs_poll_start(),
otherwise do nothing. The code prior to the blamed patch also only
looked at pcs->poll within an "if (pcs)" block.

[...]

Here is the summary with links:
  - [net-next] net: phylink: fix NULL pl->pcs dereference during phylink_pcs_poll_start
    https://git.kernel.org/netdev/net-next/c/b7d78b46d5e8

You are awesome, thank you!
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