Patch "vmci_host: fix a race condition in vmci_host_poll() causing GPF" has been added to the 6.2-stable tree

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This is a note to let you know that I've just added the patch titled

    vmci_host: fix a race condition in vmci_host_poll() causing GPF

to the 6.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     vmci_host-fix-a-race-condition-in-vmci_host_poll-cau.patch
and it can be found in the queue-6.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8df62758a90931fc3b95bd905e9c2c9eec962bf4
Author: Dae R. Jeong <threeearcat@xxxxxxxxx>
Date:   Mon Mar 27 21:01:53 2023 +0900

    vmci_host: fix a race condition in vmci_host_poll() causing GPF
    
    [ Upstream commit ae13381da5ff0e8e084c0323c3cc0a945e43e9c7 ]
    
    During fuzzing, a general protection fault is observed in
    vmci_host_poll().
    
    general protection fault, probably for non-canonical address 0xdffffc0000000019: 0000 [#1] PREEMPT SMP KASAN
    KASAN: null-ptr-deref in range [0x00000000000000c8-0x00000000000000cf]
    RIP: 0010:__lock_acquire+0xf3/0x5e00 kernel/locking/lockdep.c:4926
    <- omitting registers ->
    Call Trace:
     <TASK>
     lock_acquire+0x1a4/0x4a0 kernel/locking/lockdep.c:5672
     __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
     _raw_spin_lock_irqsave+0xb3/0x100 kernel/locking/spinlock.c:162
     add_wait_queue+0x3d/0x260 kernel/sched/wait.c:22
     poll_wait include/linux/poll.h:49 [inline]
     vmci_host_poll+0xf8/0x2b0 drivers/misc/vmw_vmci/vmci_host.c:174
     vfs_poll include/linux/poll.h:88 [inline]
     do_pollfd fs/select.c:873 [inline]
     do_poll fs/select.c:921 [inline]
     do_sys_poll+0xc7c/0x1aa0 fs/select.c:1015
     __do_sys_ppoll fs/select.c:1121 [inline]
     __se_sys_ppoll+0x2cc/0x330 fs/select.c:1101
     do_syscall_x64 arch/x86/entry/common.c:51 [inline]
     do_syscall_64+0x4e/0xa0 arch/x86/entry/common.c:82
     entry_SYSCALL_64_after_hwframe+0x46/0xb0
    
    Example thread interleaving that causes the general protection fault
    is as follows:
    
    CPU1 (vmci_host_poll)               CPU2 (vmci_host_do_init_context)
    -----                               -----
    // Read uninitialized context
    context = vmci_host_dev->context;
                                        // Initialize context
                                        vmci_host_dev->context = vmci_ctx_create();
                                        vmci_host_dev->ct_type = VMCIOBJ_CONTEXT;
    
    if (vmci_host_dev->ct_type == VMCIOBJ_CONTEXT) {
        // Dereferencing the wrong pointer
        poll_wait(..., &context->host_context);
    }
    
    In this scenario, vmci_host_poll() reads vmci_host_dev->context first,
    and then reads vmci_host_dev->ct_type to check that
    vmci_host_dev->context is initialized. However, since these two reads
    are not atomically executed, there is a chance of a race condition as
    described above.
    
    To fix this race condition, read vmci_host_dev->context after checking
    the value of vmci_host_dev->ct_type so that vmci_host_poll() always
    reads an initialized context.
    
    Reported-by: Dae R. Jeong <threeearcat@xxxxxxxxx>
    Fixes: 8bf503991f87 ("VMCI: host side driver implementation.")
    Signed-off-by: Dae R. Jeong <threeearcat@xxxxxxxxx>
    Link: https://lore.kernel.org/r/ZCGFsdBAU4cYww5l@dragonet
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/misc/vmw_vmci/vmci_host.c b/drivers/misc/vmw_vmci/vmci_host.c
index 857b9851402a6..abe79f6fd2a79 100644
--- a/drivers/misc/vmw_vmci/vmci_host.c
+++ b/drivers/misc/vmw_vmci/vmci_host.c
@@ -165,10 +165,16 @@ static int vmci_host_close(struct inode *inode, struct file *filp)
 static __poll_t vmci_host_poll(struct file *filp, poll_table *wait)
 {
 	struct vmci_host_dev *vmci_host_dev = filp->private_data;
-	struct vmci_ctx *context = vmci_host_dev->context;
+	struct vmci_ctx *context;
 	__poll_t mask = 0;
 
 	if (vmci_host_dev->ct_type == VMCIOBJ_CONTEXT) {
+		/*
+		 * Read context only if ct_type == VMCIOBJ_CONTEXT to make
+		 * sure that context is initialized
+		 */
+		context = vmci_host_dev->context;
+
 		/* Check for VMCI calls to this VM context. */
 		if (wait)
 			poll_wait(filp, &context->host_context.wait_queue,



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