Comment 0 for bug 1859522

Quan Luo and ycq from Codesafe Team of Legendsec at Qi'anxin Group reported a use-after-free issue in the i915 driver. This issue has been fixed in the upstream kernel starting in v5.2 with the following commit:

 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7dc40713618c884bf07c030d1ab1f47a9dc1f310

The flaw was introduced in v4.14 with this change:

 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1acfc104cdf8a3408f0e83b4115d4419c6315005

The problem can be fixed by expanding the usage of struct_mutex to include the GEM context lookup.