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) —[ end trace 0000000000000000 ]—

Weakness

The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.

Affected Software

References

• https://git.kernel.org/stable/c/2d12905aad462383f4e7a5fdb024d2b7ae2d10cf
• https://git.kernel.org/stable/c/c5c07c5958cf0c9af6e76813e6de15d42ee49822