[PATCH] drm/i915/gem: Don't use VMA from wrong VM in EXECBUF

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

Do not pick VMA with non-matching VM (ppGTT) on quick path
of BO handle lookup for a given EXECBUF call. VMA from wrong VM
could be picked if same BO is repeatedly used in EXECBUF
calls on same context with alternating VMs (ppGTTs).

Also avoids returning a VMA without increasing the refcount,
which may potentially lead to UAF.

References: https://lore.kernel.org/all/20260324151741.29338-1-sosohero200@gmail.com/
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index bd608cea396f..7463c3262651 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -897,6 +897,8 @@ static struct i915_vma *eb_lookup_vma(struct i915_execbuffer *eb, u32 handle)
 		vma = radix_tree_lookup(&eb->gem_context->handles_vma, handle);
 		if (likely(vma && vma->vm == vm))
 			vma = i915_vma_tryget(vma);
+		else
+			vma = NULL;
 		rcu_read_unlock();
 		if (likely(vma))
 			return vma;
-- 
2.53.0