CVE-2023-52854 Information

Description

In the Linux kernel the following vulnerability has been resolved:

padata: Fix refcnt handling in padata_free_shell()

In a high-load arm64 environment the pcrypt_aead01 test in LTP can lead to system UAF (Use-After-Free) issues. Due to the lengthy analysis of the pcrypt_aead01 function call I’ll describe the problem scenario using a simplified model:

Suppose there’s a user of padata named user_function that adheres to the padata requirement of calling padata_free_shell after serial() has been invoked as demonstrated in the following code:

struct request 
    struct padata_priv padata;
    struct completion done;
;

void parallel(struct padata_priv padata) 
    do_something();


void serial(struct padata_priv padata) 
    struct request request = container_of(padata
    				struct request
				padata);
    complete(request->done);


void user_function() 
    DECLARE_COMPLETION(done)
    padata->parallel = parallel;
    padata->serial = serial;
    padata_do_parallel();
    wait_for_completion(&done);
    padata_free_shell();

In the corresponding padata.c file there’s the following code:

static void padata_serial_worker(struct work_struct serial_work) 
    ...
    cnt = 0;

    while (!list_empty(&local_list)) 
        ...
        padata->serial(padata);
        cnt++;
    

    local_bh_enable();

    if (refcount_sub_and_test(cnt &pd->refcnt))
        padata_free_pd(pd);

Because of the high system load and the accumulation of unexecuted softirq at this moment local_bh_enable() in padata takes longer to execute than usual. Subsequently when accessing pd->refcnt pd has already been released by padata_free_shell() resulting in a UAF issue with pd->refcnt.

The fix is straightforward: add refcount_dec_and_test before calling padata_free_pd in padata_free_shell.

Reference

https://git.kernel.org/stable/c/41aad9d6953984d134fc50f631f24ef476875d4d https://git.kernel.org/stable/c/0dd34a7ad395dbcf6ae60e48e9786050e25b9bc5 https://git.kernel.org/stable/c/c7c26d0ef5d20f00dbb2ae3befcabbe0efa77275 https://git.kernel.org/stable/c/1e901bcb8af19416b65f5063a4af7996e5a51d7f https://git.kernel.org/stable/c/1734a79e951914f1db2c65e635012a35db1c674b https://git.kernel.org/stable/c/7ddc21e317b360c3444de3023bcc83b85fabae2f