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

mm/mempolicy: do not allow illegal MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()

syzbot reported access to unitialized memory in mbind() [1]

Issue came with commit bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes")

This commit added a new bit in MPOL_MODE_FLAGS, but only checked valid combination (MPOL_F_NUMA_BALANCING can only be used with MPOL_BIND) in do_set_mempolicy()

This patch moves the check in sanitize_mpol_flags() so that it is also used by mbind()

[1] BUG: KMSAN: uninit-value in __mpol_equal+0x567/0x590 mm/mempolicy.c:2260 __mpol_equal+0x567/0x590 mm/mempolicy.c:2260 mpol_equal include/linux/mempolicy.h:105 [inline] vma_merge+0x4a1/0x1e60 mm/mmap.c:1190 mbind_range+0xcc8/0x1e80 mm/mempolicy.c:811 do_mbind+0xf42/0x15f0 mm/mempolicy.c:1333 kernel_mbind mm/mempolicy.c:1483 [inline] __do_sys_mbind mm/mempolicy.c:1490 [inline] __se_sys_mbind+0x437/0xb80 mm/mempolicy.c:1486 __x64_sys_mbind+0x19d/0x200 mm/mempolicy.c:1486 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82 entry_SYSCALL_64_after_hwframe+0x44/0xae

Uninit was created at: slab_alloc_node mm/slub.c:3221 [inline] slab_alloc mm/slub.c:3230 [inline] kmem_cache_alloc+0x751/0xff0 mm/slub.c:3235 mpol_new mm/mempolicy.c:293 [inline] do_mbind+0x912/0x15f0 mm/mempolicy.c:1289 kernel_mbind mm/mempolicy.c:1483 [inline] __do_sys_mbind mm/mempolicy.c:1490 [inline] __se_sys_mbind+0x437/0xb80 mm/mempolicy.c:1486 __x64_sys_mbind+0x19d/0x200 mm/mempolicy.c:1486 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82 entry_SYSCALL_64_after_hwframe+0x44/0xae

Kernel panic - not syncing: panic_on_kmsan set ... CPU: 0 PID: 15049 Comm: syz-executor.0 Tainted: G B 5.15.0-rc2-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x1ff/0x28e lib/dump_stack.c:106 dump_stack+0x25/0x28 lib/dump_stack.c:113 panic+0x44f/0xdeb kernel/panic.c:232 kmsan_report+0x2ee/0x300 mm/kmsan/report.c:186 __msan_warning+0xd7/0x150 mm/kmsan/instrumentation.c:208 __mpol_equal+0x567/0x590 mm/mempolicy.c:2260 mpol_equal include/linux/mempolicy.h:105 [inline] vma_merge+0x4a1/0x1e60 mm/mmap.c:1190 mbind_range+0xcc8/0x1e80 mm/mempolicy.c:811 do_mbind+0xf42/0x15f0 mm/mempolicy.c:1333 kernel_mbind mm/mempolicy.c:1483 [inline] __do_sys_mbind mm/mempolicy.c:1490 [inline] __se_sys_mbind+0x437/0xb80 mm/mempolicy.c:1486 __x64_sys_mbind+0x19d/0x200 mm/mempolicy.c:1486 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82 entry_SYSCALL_64_after_hwframe+0x44/0xae