Description

In the Linux kernel, the following vulnerability has been resolved: fs/proc: fix uaf in proc_readdir_de() Pde is erased from subdir rbtree through rb_erase(), but not set the node to EMPTY, which may result in uaf access. We should use RB_CLEAR_NODE() set the erased node to EMPTY, then pde_subdir_next() will return NULL to avoid uaf access. We found an uaf issue while using stress-ng testing, need to run testcase getdent and tun in the same time. The steps of the issue is as follows: 1) use getdent to traverse dir /proc/pid/net/dev_snmp6/, and current pde is tun3; 2) in the [time windows] unregister netdevice tun3 and tun2, and erase them from rbtree. erase tun3 first, and then erase tun2. the pde(tun2) will be released to slab; 3) continue to getdent process, then pde_subdir_next() will return pde(tun2) which is released, it will case uaf access. CPU 0 | CPU 1 ------------------------------------------------------------------------- traverse dir /proc/pid/net/dev_snmp6/ | unregister_netdevice(tun->dev) //tun3 tun2 sys_getdents64() | iterate_dir() | proc_readdir() | proc_readdir_de() | snmp6_unregister_dev() pde_get(de); | proc_remove() read_unlock(&proc_subdir_lock); | remove_proc_subtree() | write_lock(&proc_subdir_lock); [time window] | rb_erase(&root->subdir_node, &parent->subdir); | write_unlock(&proc_subdir_lock); read_lock(&proc_subdir_lock); | next = pde_subdir_next(de); | pde_put(de); | de = next; //UAF | rbtree of dev_snmp6 | pde(tun3) / \ NULL pde(tun2)

References 9

• cert-portal.siemens.com https://cert-portal.siemens.com/productcert/html/ssa-253495.html
• git.kernel.org https://git.kernel.org/stable/c/03de7ff197a3d0e17d0d5c58fdac99a63cba8110
• git.kernel.org https://git.kernel.org/stable/c/1d1596d68a6f11d28f677eedf6cf5b17dbfeb491
• git.kernel.org https://git.kernel.org/stable/c/4cba73c4c89219beef7685a47374bf88b1022369
• git.kernel.org https://git.kernel.org/stable/c/623bb26127fb581a741e880e1e1a47d79aecb6f8
• git.kernel.org https://git.kernel.org/stable/c/67272c11f379d9aa5e0f6b16286b9d89b3f76046
• git.kernel.org https://git.kernel.org/stable/c/6f2482745e510ae1dacc9b090194b9c5f918d774
• git.kernel.org https://git.kernel.org/stable/c/895b4c0c79b092d732544011c3cecaf7322c36a1
• git.kernel.org https://git.kernel.org/stable/c/c81d0385500446efe48c305bbb83d47f2ae23a50

Remediation