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High severity7.8NVD Advisory· Published Jul 6, 2024· Updated Aug 4, 2026

CVE-2024-39486

CVE-2024-39486

Description

In 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, , 1) mutex_unlock(&dev->filelist_mutex) begin drm_file_update_pid mutex_lock(&dev->filelist_mutex) rcu_replace_pointer(filp->pid, , 1) mutex_unlock(&dev->filelist_mutex) get_pid() synchronize_rcu() put_pid() * pid B reaches refcount 0 and is freed here * get_pid() * UAF * synchronize_rcu() put_pid()

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.

Affected products

59

Patches

Vulnerability mechanics

References

3

News mentions

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