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In the Linux kernel, the following vulnerability has been resolved: PCI: Hold rescan lock while adding devices during host probe Since adding the PCI power control code, we may end up with a race between the pwrctl platform device rescanning the bus and host controller probe functions. The latter need to take the rescan lock when adding devices or we may end up in an undefined state having two incompletely added devices and hit the following crash when trying to remove the device over sysfs: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Internal error: Oops: 0000000096000004 [#1] SMP Call trace: __pi_strlen+0x14/0x150 kernfs_find_ns+0x80/0x13c kernfs_remove_by_name_ns+0x54/0xf0 sysfs_remove_bin_file+0x24/0x34 pci_remove_resource_files+0x3c/0x84 pci_remove_sysfs_dev_files+0x28/0x38 pci_stop_bus_device+0x8c/0xd8 pci_stop_bus_device+0x40/0xd8 pci_stop_and_remove_bus_device_locked+0x28/0x48 remove_store+0x70/0xb0 dev_attr_store+0x20/0x38 sysfs_kf_write+0x58/0x78 kernfs_fop_write_iter+0xe8/0x184 vfs_write+0x2dc/0x308 ksys_write+0x7c/0xec
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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