This is a note to let you know that I've just added the patch titled firmware: arm_scmi: Fix NULL pointer dereference in mailbox_chan_free to the 5.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: firmware-arm_scmi-fix-null-pointer-dereference-in-ma.patch and it can be found in the queue-5.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 735d9dc71927cf15b81a28b531802959b12b9f5d Author: Sudeep Holla <sudeep.holla@xxxxxxx> Date: Tue Sep 8 12:26:11 2020 +0100 firmware: arm_scmi: Fix NULL pointer dereference in mailbox_chan_free [ Upstream commit 6ed6c558234f0b6c22e47a3c2feddce3d02324dd ] scmi_mailbox is obtained from cinfo->transport_info and the first call to mailbox_chan_free frees the channel and sets cinfo->transport_info to NULL. Care is taken to check for non NULL smbox->chan but smbox can itself be NULL. Fix it by checking for it without which, kernel crashes with below NULL pointer dereference and eventually kernel panic. Unable to handle kernel NULL pointer dereference at virtual address 0000000000000038 Modules linked in: scmi_module(-) Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Sep 2 2020 pstate: 80000005 (Nzcv daif -PAN -UAO BTYPE=--) pc : mailbox_chan_free+0x2c/0x70 [scmi_module] lr : idr_for_each+0x6c/0xf8 Call trace: mailbox_chan_free+0x2c/0x70 [scmi_module] idr_for_each+0x6c/0xf8 scmi_remove+0xa8/0xf0 [scmi_module] platform_drv_remove+0x34/0x58 device_release_driver_internal+0x118/0x1f0 driver_detach+0x58/0xe8 bus_remove_driver+0x64/0xe0 driver_unregister+0x38/0x68 platform_driver_unregister+0x1c/0x28 scmi_driver_exit+0x38/0x44 [scmi_module] ---[ end trace 17bde19f50436de9 ]--- Kernel panic - not syncing: Fatal exception SMP: stopping secondary CPUs Kernel Offset: 0x1d0000 from 0xffff800010000000 PHYS_OFFSET: 0x80000000 CPU features: 0x0240022,25806004 Memory Limit: none ---[ end Kernel panic - not syncing: Fatal exception ]--- Link: https://lore.kernel.org/r/20200908112611.31515-1-sudeep.holla@xxxxxxx Fixes: 5c8a47a5a91d ("firmware: arm_scmi: Make scmi core independent of the transport type") Cc: Cristian Marussi <cristian.marussi@xxxxxxx> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx> Tested-by: Cristian Marussi <cristian.marussi@xxxxxxx> Reviewed-by: Cristian Marussi <cristian.marussi@xxxxxxx> Reviewed-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/firmware/arm_scmi/mailbox.c b/drivers/firmware/arm_scmi/mailbox.c index 6998dc86b5ce8..b797a713c3313 100644 --- a/drivers/firmware/arm_scmi/mailbox.c +++ b/drivers/firmware/arm_scmi/mailbox.c @@ -110,7 +110,7 @@ static int mailbox_chan_free(int id, void *p, void *data) struct scmi_chan_info *cinfo = p; struct scmi_mailbox *smbox = cinfo->transport_info; - if (!IS_ERR(smbox->chan)) { + if (smbox && !IS_ERR(smbox->chan)) { mbox_free_channel(smbox->chan); cinfo->transport_info = NULL; smbox->chan = NULL;