pinmux: Use sequential access to access desc->pinmux data

Overview

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

pinmux: Use sequential access to access desc->pinmux data

When two client of the same gpio call pinctrl_select_state() for the same functionality, we are seeing NULL pointer issue while accessing desc->mux_owner.

Let's say two processes A, B executing in pin_request() for the same pin and process A updates the desc->mux_usecount but not yet updated the desc->mux_owner while process B see the desc->mux_usecount which got updated by A path and further executes strcmp and while accessing desc->mux_owner it crashes with NULL pointer.

Serialize the access to mux related setting with a mutex lock.

cpu0 (process A)			cpu1(process B)

pinctrl_select_state() { pinctrl_select_state() { pin_request() { pin_request() { ... .... } else { desc->mux_usecount++; desc->mux_usecount && strcmp(desc->mux_owner, owner)) {

     if (desc->mux_usecount > 1)
           return 0;
     desc->mux_owner = owner;

} }

Affected

• Linux >= 42fed7ba44e4e8c1fb27b28ad14490cb1daff3c7 < d25e45dcf8e32062f7935e4ba154869043812ab6
• Linux >= 42fed7ba44e4e8c1fb27b28ad14490cb1daff3c7 < 2da32aed4a97ca1d70fb8b77926f72f30ce5fb4b
• Linux >= 42fed7ba44e4e8c1fb27b28ad14490cb1daff3c7 < c11e2ec9a780f54982a187ee10ffd1b810715c85
• Linux >= 42fed7ba44e4e8c1fb27b28ad14490cb1daff3c7 < 5a3e85c3c397c781393ea5fb2f45b1f60f8a4e6e
• Linux 3.10

Remediation

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