CVE-2022-49393

In the Linux kernel, the following vulnerability has been resolved:

misc: fastrpc: fix list iterator in fastrpc_req_mem_unmap_impl

This is another instance of incorrect use of list iterator and

checking it for NULL.

The list iterator value 'map' will *always* be set and non-NULL

by list_for_each_entry(), so it is incorrect to assume that the

iterator value will be NULL if the list is empty (in this case, the

check 'if (!map) {' will always be false and never exit as expected).

To fix the bug, use a new variable 'iter' as the list iterator,

while use the original variable 'map' as a dedicated pointer to

point to the found element.

Without this patch, Kernel crashes with below trace:

Unable to handle kernel access to user memory outside uaccess routines

at virtual address 0000ffff7fb03750

...

Call trace:

fastrpc_map_create+0x70/0x290 [fastrpc]

fastrpc_req_mem_map+0xf0/0x2dc [fastrpc]

fastrpc_device_ioctl+0x138/0xc60 [fastrpc]

__arm64_sys_ioctl+0xa8/0xec

invoke_syscall+0x48/0x114

el0_svc_common.constprop.0+0xd4/0xfc

do_el0_svc+0x28/0x90

el0_svc+0x3c/0x130

el0t_64_sync_handler+0xa4/0x130

el0t_64_sync+0x18c/0x190

Code: 14000016 f94000a5 eb05029f 54000260 (b94018a6)

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