CVE-2022-49196

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> powerpc/pseries: Fix use after free in remove_phb_dynamic()<br /> <br /> In remove_phb_dynamic() we use &amp;phb-&gt;io_resource, after we&amp;#39;ve called<br /> device_unregister(&amp;host_bridge-&gt;dev). But the unregister may have freed<br /> phb, because pcibios_free_controller_deferred() is the release function<br /> for the host_bridge.<br /> <br /> If there are no outstanding references when we call device_unregister()<br /> then phb will be freed out from under us.<br /> <br /> This has gone mainly unnoticed, but with slub_debug and page_poison<br /> enabled it can lead to a crash:<br /> <br /> PID: 7574 TASK: c0000000d492cb80 CPU: 13 COMMAND: "drmgr"<br /> #0 [c0000000e4f075a0] crash_kexec at c00000000027d7dc<br /> #1 [c0000000e4f075d0] oops_end at c000000000029608<br /> #2 [c0000000e4f07650] __bad_page_fault at c0000000000904b4<br /> #3 [c0000000e4f076c0] do_bad_slb_fault at c00000000009a5a8<br /> #4 [c0000000e4f076f0] data_access_slb_common_virt at c000000000008b30<br /> Data SLB Access [380] exception frame:<br /> R0: c000000000167250 R1: c0000000e4f07a00 R2: c000000002a46100<br /> R3: c000000002b39ce8 R4: 00000000000000c0 R5: 00000000000000a9<br /> R6: 3894674d000000c0 R7: 0000000000000000 R8: 00000000000000ff<br /> R9: 0000000000000100 R10: 6b6b6b6b6b6b6b6b R11: 0000000000008000<br /> R12: c00000000023da80 R13: c0000009ffd38b00 R14: 0000000000000000<br /> R15: 000000011c87f0f0 R16: 0000000000000006 R17: 0000000000000003<br /> R18: 0000000000000002 R19: 0000000000000004 R20: 0000000000000005<br /> R21: 000000011c87ede8 R22: 000000011c87c5a8 R23: 000000011c87d3a0<br /> R24: 0000000000000000 R25: 0000000000000001 R26: c0000000e4f07cc8<br /> R27: c00000004d1cc400 R28: c0080000031d00e8 R29: c00000004d23d800<br /> R30: c00000004d1d2400 R31: c00000004d1d2540<br /> NIP: c000000000167258 MSR: 8000000000009033 OR3: c000000000e9f474<br /> CTR: 0000000000000000 LR: c000000000167250 XER: 0000000020040003<br /> CCR: 0000000024088420 MQ: 0000000000000000 DAR: 6b6b6b6b6b6b6ba3<br /> DSISR: c0000000e4f07920 Syscall Result: fffffffffffffff2<br /> [NIP : release_resource+56]<br /> [LR : release_resource+48]<br /> #5 [c0000000e4f07a00] release_resource at c000000000167258 (unreliable)<br /> #6 [c0000000e4f07a30] remove_phb_dynamic at c000000000105648<br /> #7 [c0000000e4f07ab0] dlpar_remove_slot at c0080000031a09e8 [rpadlpar_io]<br /> #8 [c0000000e4f07b50] remove_slot_store at c0080000031a0b9c [rpadlpar_io]<br /> #9 [c0000000e4f07be0] kobj_attr_store at c000000000817d8c<br /> #10 [c0000000e4f07c00] sysfs_kf_write at c00000000063e504<br /> #11 [c0000000e4f07c20] kernfs_fop_write_iter at c00000000063d868<br /> #12 [c0000000e4f07c70] new_sync_write at c00000000054339c<br /> #13 [c0000000e4f07d10] vfs_write at c000000000546624<br /> #14 [c0000000e4f07d60] ksys_write at c0000000005469f4<br /> #15 [c0000000e4f07db0] system_call_exception at c000000000030840<br /> #16 [c0000000e4f07e10] system_call_vectored_common at c00000000000c168<br /> <br /> To avoid it, we can take a reference to the host_bridge-&gt;dev until we&amp;#39;re<br /> done using phb. Then when we drop the reference the phb will be freed.