[PATCH] nvme-multipath: fix flex array size in struct nvme_ns_head

[Mukesh Kumar Chaurasiya]

On Wed, May 27, 2026 at 11:50:00AM +0530, Nilay Shroff wrote:
> struct nvme_ns_head contains a flexible array member, current_path[],
> which is indexed using the NUMA node ID:
> head->current_path[numa_node_id()]
> 
> The structure is currently allocated as:
> size = sizeof(struct nvme_ns_head) +
>        (num_possible_nodes() * sizeof(struct nvme_ns *));
> head = kzalloc(size, GFP_KERNEL);
> 
> This allocation assumes that NUMA node IDs are sequential and densely
> packed from 0 .. num_possible_nodes() - 1. While this assumption holds
> on many systems, it is not always true on some architectures such as
> powerpc.
> 
> On some powerpc systems, NUMA node IDs can be sparse. For example:
> NUMA:
>   NUMA node(s):              6
>   NUMA node0 CPU(s):         80-159
>   NUMA node8 CPU(s):         0-79
>   NUMA node252 CPU(s):
>   NUMA node253 CPU(s):
>   NUMA node254 CPU(s):
>   NUMA node255 CPU(s):
> 
> That is, the possible/online NUMA node IDs are: 0, 8, 252, 253, 254, 255
> In this case: num_possible_nodes() = 6
> 
> So memory is allocated for only 6 entries in current_path[]. However,
> the array is later indexed using the actual NUMA node ID. As a result,
> accesses such as:
> head->current_path[8] or
> head->current_path[252]
> goes out of bounds, leading to the following KASAN splat:
> 
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in nvme_mpath_revalidate_paths+0x22c/0x290 [nvme_core]
> Write of size 8 at addr c00020003bda35b8 by task kworker/u641:2/1997
> 
> CPU: 1 UID: 0 PID: 1997 Comm: kworker/u641:2 Not tainted 7.1.0-rc5-dirty #14 PREEMPT(lazy)
> Hardware name: 8335-GTH POWER9 0x4e1202 opal:skiboot-v6.5.3-35-g1851b2a06 PowerNV
> Workqueue: async async_run_entry_fn
> Call Trace:
> [c000200037fa7510] [c0000000021c23d4] dump_stack_lvl+0x88/0xdc (unreliable)
> [c000200037fa7540] [c0000000009fda90] print_report+0x22c/0x67c
> [c000200037fa7630] [c0000000009fd508] kasan_report+0x108/0x220
> [c000200037fa7740] [c0000000009fff48] __asan_store8+0xe8/0x120
> [c000200037fa7760] [c008000018e76474] nvme_mpath_revalidate_paths+0x22c/0x290 [nvme_core]
> [c000200037fa7800] [c008000018e6556c] nvme_update_ns_info+0x4a4/0x5e0 [nvme_core]
> [c000200037fa7a50] [c008000018e66270] nvme_alloc_ns+0x6d8/0x1a70 [nvme_core]
> [c000200037fa7c20] [c008000018e679fc] nvme_scan_ns+0x3f4/0x630 [nvme_core]
> [c000200037fa7d10] [c00000000031f22c] async_run_entry_fn+0x9c/0x3a0
> [c000200037fa7db0] [c0000000002fa544] process_one_work+0x414/0xa10
> [c000200037fa7ec0] [c0000000002fbf00] worker_thread+0x320/0x640
> [c000200037fa7f80] [c00000000030d0f8] kthread+0x278/0x290
> [c000200037fa7fe0] [c00000000000ded8] start_kernel_thread+0x14/0x18
> 
> Allocated by task 1997 on cpu 1 at 35.928317s:
> 
> The buggy address belongs to the object at c00020003bda3000
>  which belongs to the cache kmalloc-rnd-15-2k of size 2048
> The buggy address is located 16 bytes to the right of
>  allocated 1448-byte region [c00020003bda3000, c00020003bda35a8)
> 
> The buggy address belongs to the physical page:
> 
> Memory state around the buggy address:
>  c00020003bda3480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  c00020003bda3500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >c00020003bda3580: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
>                                         ^
>  c00020003bda3600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>  c00020003bda3680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
> 
> Fix this by allocating the flexible array using nr_node_ids instead
> of num_possible_nodes(). Since nr_node_ids represents the maximum
> possible NUMA node IDs, indexing current_path[] using numa_node_id()
> becomes safe even on systems with sparse node IDs.
> 
> Fixes: f333444708f8 ("nvme: take node locality into account when selecting a path")
> Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
> ---
>  drivers/nvme/host/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index c3032d6ad6b1..96809227a0e2 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -3926,7 +3926,7 @@ static struct nvme_ns_head *nvme_alloc_ns_head(struct nvme_ctrl *ctrl,
>  	int ret = -ENOMEM;
>  
>  #ifdef CONFIG_NVME_MULTIPATH
> -	size += num_possible_nodes() * sizeof(struct nvme_ns *);
> +	size += nr_node_ids * sizeof(struct nvme_ns *);
>  #endif
>  
>  	head = kzalloc(size, GFP_KERNEL);
> -- 
> 2.53.0
> 
> 
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras at gmail.com>
Tested-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras at gmail.com>