Fixed NULL pointer deref in BYT/CHT boards

CVE-2024-46793

What is CVE-2024-46793?

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

ASoC: Intel: Boards: Fix NULL pointer deref in BYT/CHT boards harder

Since commit 13f58267cda3 ("ASoC: soc.h: don't create dummy Component via COMP_DUMMY()") dummy codecs declared like this:

SND_SOC_DAILINK_DEF(dummy, DAILINK_COMP_ARRAY(COMP_DUMMY()));

expand to:

static struct snd_soc_dai_link_component dummy[] = { };

Which means that dummy is a zero sized array and thus dais[i].codecs should not be dereferenced at all since it points to the address of the next variable stored in the data section as the "dummy" variable has an address but no size, so even dereferencing dais[0] is already an out of bounds array reference.

Which means that the if (dais[i].codecs->name) check added in commit 7d99a70b6595 ("ASoC: Intel: Boards: Fix NULL pointer deref in BYT/CHT boards") relies on that the part of the next variable which the name member maps to just happens to be NULL.

Which apparently so far it usually is, except when it isn't and then it results in crashes like this one:

[ 28.795659] BUG: unable to handle page fault for address: 0000000000030011 ... [ 28.795780] Call Trace: [ 28.795787] ... [ 28.795862] ? strcmp+0x18/0x40 [ 28.795872] 0xffffffffc150c605 [ 28.795887] platform_probe+0x40/0xa0 ... [ 28.795979] ? __pfx_init_module+0x10/0x10 [snd_soc_sst_bytcr_wm5102]

Really fix things this time around by checking dais.num_codecs != 0.

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References