CVE-2024-39486 (GCVE-0-2024-39486)

Vulnerability from cvelistv5 – Published: 2024-07-06 09:25 – Updated: 2025-05-04 09:16
VLAI?
Title
drm/drm_file: Fix pid refcounting race
Summary
In the Linux kernel, the following vulnerability has been resolved: drm/drm_file: Fix pid refcounting race <maarten.lankhorst@linux.intel.com>, Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de> 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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 031ddd28008971cce0b5626379b910d0a05fb4dd , < 16682588ead4a593cf1aebb33b36df4d1e9e4ffa (git)
Affected: 1c7a387ffef894b1ab3942f0482dac7a6e0a909c , < 0acce2a5c619ef1abdee783d7fea5eac78ce4844 (git)
Affected: 1c7a387ffef894b1ab3942f0482dac7a6e0a909c , < 4f2a129b33a2054e62273edd5a051c34c08d96e9 (git)
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    Linux Linux Affected: 6.7
Unaffected: 0 , < 6.7 (semver)
Unaffected: 6.6.37 , ≤ 6.6.* (semver)
Unaffected: 6.9.8 , ≤ 6.9.* (semver)
Unaffected: 6.10 , ≤ * (original_commit_for_fix)
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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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