Entreprise française de cybersécurité depuis 2004
☎ 03 60 47 09 81 - info@securiteinfo.com
☎ 03 60 47 09 81 - info@securiteinfo.com
In the Linux kernel, the following vulnerability has been resolved:net: Fix null-ptr-deref by sock_lock_init_class_and_name() and rmmod.When I ran the repro [0] and waited a few seconds, I observed twoLOCKDEP splats: a warning immediately followed by a null-ptr-deref. [1]Reproduction Steps: 1) Mount CIFS 2) Add an iptables rule to drop incoming FIN packets for CIFS 3) Unmount CIFS 4) Unload the CIFS module 5) Remove the iptables ruleAt step 3), the CIFS module calls sock_release() for the underlyingTCP socket, and it returns quickly. However, the socket remains inFIN_WAIT_1 because incoming FIN packets are dropped.At this point, the module's refcnt is 0 while the socket is stillalive, so the following rmmod command succeeds. # ss -tan State Recv-Q Send-Q Local Address:Port Peer Address:Port FIN-WAIT-1 0 477 10.0.2.15:51062 10.0.0.137:445 # lsmod | grep cifs cifs 1159168 0This highlights a discrepancy between the lifetime of the CIFS moduleand the underlying TCP socket. Even after CIFS calls sock_release()and it returns, the TCP socket does not die immediately in order toclose the connection gracefully.While this is generally fine, it causes an issue with LOCKDEP becauseCIFS assigns a different lock class to the TCP socket's sk->sk_lockusing sock_lock_init_class_and_name().Once an incoming packet is processed for the socket or a timer fires,sk->sk_lock is acquired.Then, LOCKDEP checks the lock context in check_wait_context(), wherehlock_class() is called to retrieve the lock class. However, sincethe module has already been unloaded, hlock_class() logs a warningand returns NULL, triggering the null-ptr-deref.If LOCKDEP is enabled, we must ensure that a module callingsock_lock_init_class_and_name() (CIFS, NFS, etc) cannot be unloadedwhile such a socket is still alive to prevent this issue.Let's hold the module reference in sock_lock_init_class_and_name()and release it when the socket is freed in sk_prot_free().Note that sock_lock_init() clears sk->sk_owner for svc_create_socket()that calls sock_lock_init_class_and_name() for a listening socket,which clones a socket by sk_clone_lock() without GFP_ZERO.[0]:CIFS_SERVER="10.0.0.137"CIFS_PATH="//${CIFS_SERVER}/Users/Administrator/Desktop/CIFS_TEST"DEV="enp0s3"CRED="/root/WindowsCredential.txt"MNT=$(mktemp -d /tmp/XXXXXX)mount -t cifs ${CIFS_PATH} ${MNT} -o vers=3.0,credentials=${CRED},cache=none,echo_interval=1iptables -A INPUT -s ${CIFS_SERVER} -j DROPfor i in $(seq 10);do umount ${MNT} rmmod cifs sleep 1donerm -r ${MNT}iptables -D INPUT -s ${CIFS_SERVER} -j DROP[1]:DEBUG_LOCKS_WARN_ON(1)WARNING: CPU: 10 PID: 0 at kernel/locking/lockdep.c:234 hlock_class (kernel/locking/lockdep.c:234 kernel/locking/lockdep.c:223)Modules linked in: cifs_arc4 nls_ucs2_utils cifs_md4 [last unloaded: cifs]CPU: 10 UID: 0 PID: 0 Comm: swapper/10 Not tainted 6.14.0 #36Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014RIP: 0010:hlock_class (kernel/locking/lockdep.c:234 kernel/locking/lockdep.c:223)...Call Trace:
No PoCs from references.
- https://github.com/fkie-cad/nvd-json-data-feeds
- https://github.com/w4zu/Debian_security