net: mvpp2: guard flow control update with global_tx_fc in buffer switching

Overview

In the Linux kernel, the following vulnerability has been resolved:

net: mvpp2: guard flow control update with global_tx_fc in buffer switching

mvpp2_bm_switch_buffers() unconditionally calls mvpp2_bm_pool_update_priv_fc() when switching between per-cpu and shared buffer pool modes. This function programs CM3 flow control registers via mvpp2_cm3_read()/mvpp2_cm3_write(), which dereference priv->cm3_base without any NULL check.

When the CM3 SRAM resource is not present in the device tree (the third reg entry added by commit 60523583b07c ("dts: marvell: add CM3 SRAM memory to cp11x ethernet device tree")), priv->cm3_base remains NULL and priv->global_tx_fc is false. Any operation that triggers mvpp2_bm_switch_buffers(), for example an MTU change that crosses the jumbo frame threshold, will crash:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Mem abort info: ESR = 0x0000000096000006 EC = 0x25: DABT (current EL), IL = 32 bits pc : readl+0x0/0x18 lr : mvpp2_cm3_read.isra.0+0x14/0x20 Call trace: readl+0x0/0x18 mvpp2_bm_pool_update_fc+0x40/0x12c mvpp2_bm_pool_update_priv_fc+0x94/0xd8 mvpp2_bm_switch_buffers.isra.0+0x80/0x1c0 mvpp2_change_mtu+0x140/0x380 __dev_set_mtu+0x1c/0x38 dev_set_mtu_ext+0x78/0x118 dev_set_mtu+0x48/0xa8 dev_ifsioc+0x21c/0x43c dev_ioctl+0x2d8/0x42c sock_ioctl+0x314/0x378

Every other flow control call site in the driver already guards hardware access with either priv->global_tx_fc or port->tx_fc. mvpp2_bm_switch_buffers() is the only place that omits this check.

Add the missing priv->global_tx_fc guard to both the disable and re-enable calls in mvpp2_bm_switch_buffers(), consistent with the rest of the driver.

Affected

• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < 0cfcd31f98fc608dc9406bff3fee3a9dd364d014
• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < da089f74a993f846685067b14158cb41b879ff29
• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < ff0c54f088f7ab91dbbf47cf8244460f99122750
• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < 7bd20f4b3ef3044dc55acd5b8ef748a70d29d03f
• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < 7df2b50cae1a76cbb90b294f3edb61e3e10bf2e9
• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < 8baced53a35fc9710f80d6ca016a2c418dc3231f
• Linux >= 3a616b92a9d17448d96a33bf58e69f01457fd43a < 8a63baadf08453f66eb582fdb6dd234f72024723
• Linux 5.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.