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In the Linux kernel, the following vulnerability has been resolved: xhci: Fix Panther point NULL pointer deref at full-speed re-enumeration re-enumerating full-speed devices after a failed address device command can trigger a NULL pointer dereference. Full-speed devices may need to reconfigure the endpoint 0 Max Packet Size value during enumeration. Usb core calls usb_ep0_reinit() in this case, which ends up calling xhci_configure_endpoint(). On Panther point xHC the xhci_configure_endpoint() function will additionally check and reserve bandwidth in software. Other hosts do this in hardware If xHC address device command fails then a new xhci_virt_device structure is allocated as part of re-enabling the slot, but the bandwidth table pointers are not set up properly here. This triggers the NULL pointer dereference the next time usb_ep0_reinit() is called and xhci_configure_endpoint() tries to check and reserve bandwidth [46710.713538] usb 3-1: new full-speed USB device number 5 using xhci_hcd [46710.713699] usb 3-1: Device not responding to setup address. [46710.917684] usb 3-1: Device not responding to setup address. [46711.125536] usb 3-1: device not accepting address 5, error -71 [46711.125594] BUG: kernel NULL pointer dereference, address: 0000000000000008 [46711.125600] #PF: supervisor read access in kernel mode [46711.125603] #PF: error_code(0x0000) - not-present page [46711.125606] PGD 0 P4D 0 [46711.125610] Oops: Oops: 0000 [#1] PREEMPT SMP PTI [46711.125615] CPU: 1 PID: 25760 Comm: kworker/1:2 Not tainted 6.10.3_2 #1 [46711.125620] Hardware name: Gigabyte Technology Co., Ltd. [46711.125623] Workqueue: usb_hub_wq hub_event [usbcore] [46711.125668] RIP: 0010:xhci_reserve_bandwidth (drivers/usb/host/xhci.c Fix this by making sure bandwidth table pointers are set up correctly after a failed address device command, and additionally by avoiding checking for bandwidth in cases like this where no actual endpoints are added or removed, i.e. only context for default control endpoint 0 is evaluated.
CVSS 3.1 Base Score 5.5. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).
While there are no complete fixes aside from conscientious programming, the following steps will go a long way to ensure that NULL pointer dereferences do not occur.
}
/* make use of pointer1 *//* ... */If you are working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished.
This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.
}
strcpy(hostname, hp->h_name);/*routine that ensures user_supplied_addr is in the right format for conversion */If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference would then occur in the call to strcpy().
Note that this example is also vulnerable to a buffer overflow (see CWE-119).
In the following code, the programmer assumes that the system always has a property named "cmd" defined. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method.
cmd = cmd.trim();This application has registered to handle a URL when sent an intent:
}......
}
}int length = URL.length();...The application assumes the URL will always be included in the intent. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called.
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