Re: [PATCH net v3 1/3] vsock: Fix transport_{g2h,h2g} TOCTOU
From: Stefano Garzarella <sgarzare@redhat.com>
Date: 2025-07-03 08:18:48
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On Wed, Jul 02, 2025 at 03:38:43PM +0200, Michal Luczaj wrote:
vsock_find_cid() and vsock_dev_do_ioctl() may race with module unload.
transport_{g2h,h2g} may become NULL after the NULL check.
Introduce vsock_transport_local_cid() to protect from a potential
null-ptr-deref.
KASAN: null-ptr-deref in range [0x0000000000000118-0x000000000000011f]
RIP: 0010:vsock_find_cid+0x47/0x90
Call Trace:
__vsock_bind+0x4b2/0x720
vsock_bind+0x90/0xe0
__sys_bind+0x14d/0x1e0
__x64_sys_bind+0x6e/0xc0
do_syscall_64+0x92/0x1c0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
KASAN: null-ptr-deref in range [0x0000000000000118-0x000000000000011f]
RIP: 0010:vsock_dev_do_ioctl.isra.0+0x58/0xf0
Call Trace:
__x64_sys_ioctl+0x12d/0x190
do_syscall_64+0x92/0x1c0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Michal Luczaj <redacted>
---
net/vmw_vsock/af_vsock.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Thanks! Stefano
quoted hunk ↗ jump to hunk
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 2e7a3034e965db30b6ee295370d866e6d8b1c341..39473b9e0829f240045262aef00cbae82a425dcc 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c@@ -531,9 +531,25 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)} EXPORT_SYMBOL_GPL(vsock_assign_transport); +/* + * Provide safe access to static transport_{h2g,g2h,dgram,local} callbacks. + * Otherwise we may race with module removal. Do not use on `vsk->transport`. + */ +static u32 vsock_registered_transport_cid(const struct vsock_transport **transport) +{ + u32 cid = VMADDR_CID_ANY; + + mutex_lock(&vsock_register_mutex); + if (*transport) + cid = (*transport)->get_local_cid(); + mutex_unlock(&vsock_register_mutex); + + return cid; +} + bool vsock_find_cid(unsigned int cid) { - if (transport_g2h && cid == transport_g2h->get_local_cid()) + if (cid == vsock_registered_transport_cid(&transport_g2h)) return true; if (transport_h2g && cid == VMADDR_CID_HOST)@@ -2536,18 +2552,17 @@ static long vsock_dev_do_ioctl(struct file *filp,unsigned int cmd, void __user *ptr) { u32 __user *p = ptr; - u32 cid = VMADDR_CID_ANY; int retval = 0; + u32 cid; switch (cmd) { case IOCTL_VM_SOCKETS_GET_LOCAL_CID: /* To be compatible with the VMCI behavior, we prioritize the * guest CID instead of well-know host CID (VMADDR_CID_HOST). */ - if (transport_g2h) - cid = transport_g2h->get_local_cid(); - else if (transport_h2g) - cid = transport_h2g->get_local_cid(); + cid = vsock_registered_transport_cid(&transport_g2h); + if (cid == VMADDR_CID_ANY) + cid = vsock_registered_transport_cid(&transport_h2g); if (put_user(cid, p) != 0) retval = -EFAULT; -- 2.49.0