In the Linux kernel, the following vulnerability has been resolved:
drm/gem: Try to fix change_handle ioctl, attempt 4
[airlied: just added some comments on how to reenable]
On-list because the cat is out of the bag and we're clearly not good
enough to figure this out in private. The story thus far:
5e28b7b94408 ("drm: Set old handle to NULL before prime swap in
change_handle") tried to fix a race condition between the gem_close and
gem_change_handle ioctls, but got a few things wrong:
- There's a confusion with the local variable handle, which is actually
the new handle, and so the two-stage trick was actually applied to the
wrong idr slot. 7164d78559b0 ("drm/gem: fix race between
change_handle and handle_delete") tried to fix that by adding yet
another code block, but forgot to add the error handling. Which meant
we now have two paths, both kinda wrong.
- dc366607c41c ("drm: Replace old pointer to new idr") tried to apply
another fix, but inconsistently, again because of the handle confusion
- this would be the right fix (kinda, somewhat, it's a mess) if we'd
do the two-stage approach for the new handle. Except that wasn't the
intent of the original fix.
We also didn't have an igt merged for the original ioctl, which is a big
no-go. This was attempted to address off-list in the original bugfix,
and amd QA people claimed the bug was fixed now. Very clearly that's not
the case. Here's my attempt to sort this out:
- Rename the local variable to new_handle, the old aliasing with
args->handle is just too dangerously confusing.
- Merge the gem obj lookup with the two-stage idr_replace so that we
avoid getting ourselves confused there.
- This means we don't have a surplus temporary reference anymore, only
an inherited from the idr. A concurrent gem_close on the new_handle
could steal that. Fix that with the same two-stage approach
create_tail uses. This is a bit overkill as documented in the comment,
but I also don't trust my ability to understand this all correctly, so
go with the established pattern we have from other ioctls instead for
maximum paranoia.
- Adjust error paths. I've tried to make the error and success paths
common, because they are identical except for which handle is removed
and on which we call idr_replace to (re)install the object again. But
that made things messier to read, so I've left it at the more verbose
version, which unfortunately hides the symmetry in the entire code
flow a bit.
- While at it, also replace the 7 space indent with 1 tab.
And finally, because I flat out don't trust my abilities here at all
anymore:
- Disable the ioctl until we have the igt situation and everything else
sorted out on-list and with full consensus.
v2:
Sashiko noticed that I didn't handle the error path for idr_replace
correctly, it must be checked with IS_ERR_OR_NULL like in
gem_handle_delete. So yeah, definitely should just the existing paths
1:1 because this is endless amounts of tricky.
Also add the Fixes: line for the original ioctl, I forgot that too.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.8): severity, escalated by confirmed exploitation. This CVE's 7.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.1% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-09). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it