drm/drm_file: Fix pid refcounting race

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2024-39486
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2024-07-06 10:15:03 UTC
Updated2026-08-04 11:18:59 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: drm/drm_file: Fix pid refcounting race <[email protected]>, Maxime Ripard <[email protected]>, Thomas Zimmermann <[email protected]> filp->pid is supposed to be a refcounted pointer; however, before this patch, drm_file_update_pid() only increments the refcount of a struct pid after storing a pointer to it in filp->pid and dropping the dev->filelist_mutex, making the following race possible: process A process B ========= ========= begin drm_file_update_pid mutex_lock(&dev->filelist_mutex) rcu_replace_pointer(filp->pid, <pid B>, 1) mutex_unlock(&dev->filelist_mutex) begin drm_file_update_pid mutex_lock(&dev->filelist_mutex) rcu_replace_pointer(filp->pid, <pid A>, 1) mutex_unlock(&dev->filelist_mutex) get_pid(<pid A>) synchronize_rcu() put_pid(<pid B>) *** pid B reaches refcount 0 and is freed here *** get_pid(<pid B>) *** UAF *** synchronize_rcu() put_pid(<pid A>) As far as I know, this race can only occur with CONFIG_PREEMPT_RCU=y because it requires RCU to detect a quiescent state in code that is not explicitly calling into the scheduler. This race leads to use-after-free of a "struct pid". It is probably somewhat hard to hit because process A has to pass through a synchronize_rcu() operation while process B is between mutex_unlock() and get_pid(). Fix it by ensuring that by the time a pointer to the current task's pid is stored in the file, an extra reference to the pid has been taken. This fix also removes the condition for synchronize_rcu(); I think that optimization is unnecessary complexity, since in that case we would usually have bailed out on the lockless check above.

Risk And Classification

Primary CVSS: v3.1 7 HIGH from [email protected]

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Problem Types: CWE-416

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary7HIGHCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 031ddd28008971cce0b5626379b910d0a05fb4dd 16682588ead4a593cf1aebb33b36df4d1e9e4ffa git Not specified
CNA Linux Linux affected 1c7a387ffef894b1ab3942f0482dac7a6e0a909c 0acce2a5c619ef1abdee783d7fea5eac78ce4844 git Not specified
CNA Linux Linux affected 1c7a387ffef894b1ab3942f0482dac7a6e0a909c 4f2a129b33a2054e62273edd5a051c34c08d96e9 git Not specified
CNA Linux Linux affected 6.6.9 6.6.37 semver Not specified
CNA Linux Linux affected 6.7 Not specified
CNA Linux Linux unaffected 6.7 semver Not specified
CNA Linux Linux unaffected 6.6.37 6.6.* semver Not specified
CNA Linux Linux unaffected 6.9.8 6.9.* semver Not specified
CNA Linux Linux unaffected 6.10 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0acce2a5c619ef1abdee783d7fea5eac78ce4844 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/16682588ead4a593cf1aebb33b36df4d1e9e4ffa af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/4f2a129b33a2054e62273edd5a051c34c08d96e9 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
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