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In the Linux kernel, the following vulnerability has been resolved: iommufd: Require drivers to supply the cache_invalidate_user ops If drivers don't do this then iommufd will oops invalidation ioctls with something like: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Mem abort info: ESR = 0x0000000086000004 EC = 0x21: IABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x04: level 0 translation fault user pgtable: 4k pages, 48-bit VAs, pgdp=0000000101059000 [0000000000000000] pgd=0000000000000000, p4d=0000000000000000 Internal error: Oops: 0000000086000004 [#1] PREEMPT SMP Modules linked in: CPU: 2 PID: 371 Comm: qemu-system-aar Not tainted 6.8.0-rc7-gde77230ac23a #9 Hardware name: linux,dummy-virt (DT) pstate: 81400809 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=-c) pc : 0x0 lr : iommufd_hwpt_invalidate+0xa4/0x204 sp : ffff800080f3bcc0 x29: ffff800080f3bcf0 x28: ffff0000c369b300 x27: 0000000000000000 x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 x23: 0000000000000000 x22: 00000000c1e334a0 x21: ffff0000c1e334a0 x20: ffff800080f3bd38 x19: ffff800080f3bd58 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000ffff8240d6d8 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000 x8 : 0000001000000002 x7 : 0000fffeac1ec950 x6 : 0000000000000000 x5 : ffff800080f3bd78 x4 : 0000000000000003 x3 : 0000000000000002 x2 : 0000000000000000 x1 : ffff800080f3bcc8 x0 : ffff0000c6034d80 Call trace: 0x0 iommufd_fops_ioctl+0x154/0x274 __arm64_sys_ioctl+0xac/0xf0 invoke_syscall+0x48/0x110 el0_svc_common.constprop.0+0x40/0xe0 do_el0_svc+0x1c/0x28 el0_svc+0x34/0xb4 el0t_64_sync_handler+0x120/0x12c el0t_64_sync+0x190/0x194 All existing drivers implement this op for nesting, this is mostly a bisection aid.
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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