The patch titled Subject: sched/numa: fix the potential null pointer dereference in task_numa_work() has been added to the -mm mm-hotfixes-unstable branch. Its filename is sched-numa-fix-the-potential-null-pointer-dereference-in-task_numa_work.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Shawn Wang shawnwang@linux.alibaba.com Subject: sched/numa: fix the potential null pointer dereference in task_numa_work() Date: Fri, 25 Oct 2024 10:22:08 +0800

When running stress-ng-vm-segv test, we found a null pointer dereference error in task_numa_work(). Here is the backtrace:

[323676.066985] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020 ...... [323676.067108] CPU: 35 PID: 2694524 Comm: stress-ng-vm-se ...... [323676.067113] pstate: 23401009 (nzCv daif +PAN -UAO +TCO +DIT +SSBS BTYPE=--) [323676.067115] pc : vma_migratable+0x1c/0xd0 [323676.067122] lr : task_numa_work+0x1ec/0x4e0 [323676.067127] sp : ffff8000ada73d20 [323676.067128] x29: ffff8000ada73d20 x28: 0000000000000000 x27: 000000003e89f010 [323676.067130] x26: 0000000000080000 x25: ffff800081b5c0d8 x24: ffff800081b27000 [323676.067133] x23: 0000000000010000 x22: 0000000104d18cc0 x21: ffff0009f7158000 [323676.067135] x20: 0000000000000000 x19: 0000000000000000 x18: ffff8000ada73db8 [323676.067138] x17: 0001400000000000 x16: ffff800080df40b0 x15: 0000000000000035 [323676.067140] x14: ffff8000ada73cc8 x13: 1fffe0017cc72001 x12: ffff8000ada73cc8 [323676.067142] x11: ffff80008001160c x10: ffff000be639000c x9 : ffff8000800f4ba4 [323676.067145] x8 : ffff000810375000 x7 : ffff8000ada73974 x6 : 0000000000000001 [323676.067147] x5 : 0068000b33e26707 x4 : 0000000000000001 x3 : ffff0009f7158000 [323676.067149] x2 : 0000000000000041 x1 : 0000000000004400 x0 : 0000000000000000 [323676.067152] Call trace: [323676.067153] vma_migratable+0x1c/0xd0 [323676.067155] task_numa_work+0x1ec/0x4e0 [323676.067157] task_work_run+0x78/0xd8 [323676.067161] do_notify_resume+0x1ec/0x290 [323676.067163] el0_svc+0x150/0x160 [323676.067167] el0t_64_sync_handler+0xf8/0x128 [323676.067170] el0t_64_sync+0x17c/0x180 [323676.067173] Code: d2888001 910003fd f9000bf3 aa0003f3 (f9401000) [323676.067177] SMP: stopping secondary CPUs [323676.070184] Starting crashdump kernel...

stress-ng-vm-segv in stress-ng is used to stress test the SIGSEGV error handling function of the system, which tries to cause a SIGSEGV error on return from unmapping the whole address space of the child process.

Normally this program will not cause kernel crashes. But before the munmap system call returns to user mode, a potential task_numa_work() for numa balancing could be added and executed. In this scenario, since the child process has no vma after munmap, the vma_next() in task_numa_work() will return a null pointer even if the vma iterator restarts from 0.

Recheck the vma pointer before dereferencing it in task_numa_work().

Link: https://lkml.kernel.org/r/20241025022208.125527-1-shawnwang@linux.alibaba.co... Fixes: 214dbc428137 ("sched: convert to vma iterator") Signed-off-by: Shawn Wang shawnwang@linux.alibaba.com Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Ben Segall bsegall@google.com Cc: Dietmar Eggemann dietmar.eggemann@arm.com Cc: Ingo Molnar mingo@redhat.com Cc: Juri Lelli juri.lelli@redhat.com Cc: Mel Gorman mgorman@suse.de Cc: Peter Zijlstra peterz@infradead.org Cc: Steven Rostedt (Google) rostedt@goodmis.org Cc: Valentin Schneider vschneid@redhat.com Cc: Vincent Guittot vincent.guittot@linaro.org Cc: stable@vger.kernel.org [6.2+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/sched/fair.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/sched/fair.c~sched-numa-fix-the-potential-null-pointer-dereference-in-task_numa_work +++ a/kernel/sched/fair.c @@ -3369,7 +3369,7 @@ retry_pids: vma = vma_next(&vmi); }

- do { + for (; vma; vma = vma_next(&vmi)) { if (!vma_migratable(vma) || !vma_policy_mof(vma) || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_MIXEDMAP)) { trace_sched_skip_vma_numa(mm, vma, NUMAB_SKIP_UNSUITABLE); @@ -3491,7 +3491,7 @@ retry_pids: */ if (vma_pids_forced) break; - } for_each_vma(vmi, vma); + }

/* * If no VMAs are remaining and VMAs were skipped due to the PID _

Patches currently in -mm which might be from shawnwang@linux.alibaba.com are

sched-numa-fix-the-potential-null-pointer-dereference-in-task_numa_work.patch