Re: [PATCH V1] nvmem: core: fix memory abort in cleanup path

[Thierry Reding <treding@nvidia.com>]

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On Sat, Dec 28, 2019 at 08:02:42PM -0800, Bitan Biswas wrote:
> nvmem_cell_info_to_nvmem_cell implementation has static
> allocation of name. nvmem_add_cells_from_of() call may
> return error and kfree name results in memory abort. Use
> kasprintf() instead of assigning pointer and prevent kfree crash.
> 
> [    8.076461] Unable to handle kernel paging request at virtual address ffffffffffe44888
> [    8.084762] Mem abort info:
> [    8.087694]   ESR = 0x96000006
> [    8.090906]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    8.096476]   SET = 0, FnV = 0
> [    8.099683]   EA = 0, S1PTW = 0
> [    8.102976] Data abort info:
> [    8.106004]   ISV = 0, ISS = 0x00000006
> [    8.110026]   CM = 0, WnR = 0
> [    8.113154] swapper pgtable: 64k pages, 48-bit VAs, pgdp=00000000815d0000
> [    8.120279] [ffffffffffe44888] pgd=0000000081d30803, pud=0000000081d30803, pmd=0000000000000000
> [    8.129429] Internal error: Oops: 96000006 [#1] PREEMPT SMP
> [    8.135257] Modules linked in:
> [    8.138456] CPU: 2 PID: 43 Comm: kworker/2:1 Tainted: G S                5.5.0-rc3-tegra-00051-g6989dd3-dirty #3   [    8.149098] Hardware name: quill (DT)
> [    8.152968] Workqueue: events deferred_probe_work_func
> [    8.158350] pstate: a0000005 (NzCv daif -PAN -UAO)
> [    8.163386] pc : kfree+0x38/0x278
> [    8.166873] lr : nvmem_cell_drop+0x68/0x80
> [    8.171154] sp : ffff80001284f9d0
> [    8.174620] x29: ffff80001284f9d0 x28: ffff0001f677e830
> [    8.180189] x27: ffff800011b0b000 x26: ffff0001c36e1008
> [    8.185755] x25: ffff8000112ad000 x24: ffff8000112c9000
> [    8.191311] x23: ffffffffffffffea x22: ffff800010adc7f0
> [    8.196865] x21: ffffffffffe44880 x20: ffff800011b0b068
> [    8.202424] x19: ffff80001122d380 x18: ffffffffffffffff
> [    8.207987] x17: 00000000d5cb4756 x16: 0000000070b193b8
> [    8.213550] x15: ffff8000119538c8 x14: 0720072007200720
> [    8.219120] x13: 07200720076e0772 x12: 07750762072d0765
> [    8.224685] x11: 0773077507660765 x10: 072f073007300730
> [    8.230253] x9 : 0730073207380733 x8 : 0000000000000151
> [    8.235818] x7 : 07660765072f0720 x6 : ffff0001c00e0f00
> [    8.241382] x5 : 0000000000000000 x4 : ffff0001c0b43800
> [    8.247007] x3 : ffff800011b0b068 x2 : 0000000000000000
> [    8.252567] x1 : 0000000000000000 x0 : ffffffdfffe00000
> [    8.258126] Call trace:
> [    8.260705]  kfree+0x38/0x278
> [    8.263827]  nvmem_cell_drop+0x68/0x80
> [    8.267773]  nvmem_device_remove_all_cells+0x2c/0x50
> [    8.272988]  nvmem_register.part.9+0x520/0x628
> [    8.277655]  devm_nvmem_register+0x48/0xa0
> [    8.281966]  tegra_fuse_probe+0x140/0x1f0
> [    8.286181]  platform_drv_probe+0x50/0xa0
> [    8.290397]  really_probe+0x108/0x348
> [    8.294243]  driver_probe_device+0x58/0x100
> [    8.298618]  __device_attach_driver+0x90/0xb0
> [    8.303172]  bus_for_each_drv+0x64/0xc8
> [    8.307184]  __device_attach+0xd8/0x138
> [    8.311195]  device_initial_probe+0x10/0x18
> [    8.315562]  bus_probe_device+0x90/0x98
> [    8.319572]  deferred_probe_work_func+0x74/0xb0
> [    8.324304]  process_one_work+0x1e0/0x358
> [    8.328490]  worker_thread+0x208/0x488
> [    8.332411]  kthread+0x118/0x120
> [    8.335783]  ret_from_fork+0x10/0x18
> [    8.339561] Code: d350feb5 f2dffbe0 aa1e03f6 8b151815 (f94006a0)
> [    8.345939] ---[ end trace 49b1303c6b83198e ]---
> 
> Fixes: badcdff107cbf ("nvmem: Convert to using %pOFn instead of device_node.name")
> 
> Signed-off-by: Bitan Biswas <bbiswas@nvidia.com>
> ---
>  drivers/nvmem/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 9f1ee9c..0fc66e1 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -110,7 +110,7 @@ static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
>  	cell->nvmem = nvmem;
>  	cell->offset = info->offset;
>  	cell->bytes = info->bytes;
> -	cell->name = info->name;
> +	cell->name = kasprintf(GFP_KERNEL, "%s", info->name);

kstrdup() seems more appropriate here.

A slightly more efficient way to do this would be to use a combination
of kstrdup_const() and kfree_const(), which would allow read-only
strings to be replicated by simple assignment rather than duplication.
Note that in that case you'd need to carefully replace all kfree() calls
on cell->name by a kfree_const() to ensure they do the right thing.

Thierry

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