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Vulnerability CVE-2024-39486
Published: 2024-07-06
| Description: |
In the Linux kernel, the following vulnerability has been resolved:
drm/drm_file: Fix pid refcounting race
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. |
See advisories in our WLB2 database: | Topic | Author | Date |
High |
| Jann Horn | 06.08.2024 |
Type:
CWE-362
References: |
https://git.kernel.org/stable/c/16682588ead4a593cf1aebb33b36df4d1e9e4ffa
https://git.kernel.org/stable/c/0acce2a5c619ef1abdee783d7fea5eac78ce4844
https://git.kernel.org/stable/c/4f2a129b33a2054e62273edd5a051c34c08d96e9
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