RE: [PATCH v2] mpt3sas: Avoid test/set_bit() operating in non-allocated memory

[David Laight]

From: Breno Leitao <leitao@xxxxxxxxxx>
> Sent: 05 June 2024 09:55
> 
> There is a potential out-of-bounds access when using test_bit() on a
> single word. The test_bit() and set_bit() functions operate on long
> values, and when testing or setting a single word, they can exceed the
> word boundary. KASAN detects this issue and produces a dump:
> 
> 	 BUG: KASAN: slab-out-of-bounds in _scsih_add_device.constprop.0
> (./arch/x86/include/asm/bitops.h:60 ./include/asm-generic/bitops/instrumented-atomic.h:29
> drivers/scsi/mpt3sas/mpt3sas_scsih.c:7331) mpt3sas
> 
> 	 Write of size 8 at addr ffff8881d26e3c60 by task kworker/u1536:2/2965
> 
> For full log, please look at [1].
> 
> Make the allocation at least the size of sizeof(unsigned long) so that
> set_bit() and test_bit() have sufficient room for read/write operations
> without overwriting unallocated memory.
> 
...
> @@ -8512,6 +8512,12 @@ mpt3sas_base_attach(struct MPT3SAS_ADAPTER *ioc)
>  	ioc->pd_handles_sz = (ioc->facts.MaxDevHandle / 8);
>  	if (ioc->facts.MaxDevHandle % 8)
>  		ioc->pd_handles_sz++;
> +	/* pd_handles_sz should have, at least, the minimal room
> +	 * for set_bit()/test_bit(), otherwise out-of-memory touch
> +	 * may occur
> +	 */
> +	ioc->pd_handles_sz = ALIGN(ioc->pd_handles_sz, sizeof(unsigned long));
> +
>  	ioc->pd_handles = kzalloc(ioc->pd_handles_sz,
>  	    GFP_KERNEL);

That is entirely stupid code.
IIRC there is a BITMAP_SIZE() that does ((x) + 63u) & ~63)/8
(on 64bit systems).

	David

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