drm/exec: don't immediately add prelocked obj to array of locked objs
Impact
In the Linux kernel, the following vulnerability has been resolved:
Source excerpt · LinuxAffected packages
Affected products
Vendor version evidence. Product records are separate from automatic dependency matching.
Linux · Linux
Other versions: unaffected
| Version / range | Source status |
|---|---|
| 09593216bff15866f95c8ad406cb7fdcec1ee40a to before 96d9996e5dbcfabed052c0d9377a382c95fed607 | affected |
| 09593216bff15866f95c8ad406cb7fdcec1ee40a to before 7a10cd79c4d9a90334fece32fef3a8e5b1a9727b | affected |
| 09593216bff15866f95c8ad406cb7fdcec1ee40a to before 26401a4999f1596a515b2e704e7066ac09306488 | affected |
Linux · Linux
Other versions: affected
| Version / range | Source status |
|---|---|
| 6.6 | affected |
| 0 to before 6.6 | unaffected |
| 6.18.59 through 6.18.* (inclusive) | unaffected |
| 7.2.13 through 7.2.* (inclusive) | unaffected |
| 7.3 through * (inclusive) | unaffected |
Original source description
In the Linux kernel, the following vulnerability has been resolved:
drm/exec: don't immediately add prelocked obj to array of locked objs
When a contention is detected the drm_exec object grabs a reference to the contended object, unlocks all other objects and pre-locks the contended one before anything else.
The problem is that it is possible that this pre-locked object was about to be destroyed and drm_exec is now holding the last reference to it.
So we never actually see this pre-locked object again to be explicitly locked and so also never reserve a slot for a dma_fence object on it.
Should the driver now use drm_exec_for_each_locked_object() to add a new fence to all locked objects we eventually see a warning or even a BUG_ON() to prevent random memory corruption.
Fix this by keeping the prelocked object out of the array of locked objs until it was explicitly mentioned by the driver again.
If the prelocked object is never mentioned again by the driver just unlock and drop the reference at the end of the locking loop.