[PATCH] mtd: intel-dg: fix array-index-out-of-bounds in intel_dg_mtd_probe()

[Gustavo A. R. Silva]

Fix the UBSAN: array-index-out-of-bounds issue below by updating
counter nvm->nregions before the first access to flexible-array
member nvm->regions[].

from kernel bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=220823

Dec 15 22:01:52 orpheus kernel: UBSAN: array-index-out-of-bounds in /var/tmp/portage/sys-kernel/gentoo-kernel-6.18.1/work/linux-6.18/drivers/mtd/devices/mtd_intel_dg.c:750:15

Notice that this flexible array is annotated with the counted_by()
attribute, hence the counter must always be updated before the
first access to the array.

Cc: stable at vger.kernel.org
Fixes: ceb5ab3cb646 ("mtd: add driver for intel graphics non-volatile memory device")
Reported-by: Randy Dunlap <rdunlap at infradead.org>
Closes: https://lore.kernel.org/linux-hardening/90e419ad-4036-4669-a4cc-8ce5d29e464b@infradead.org/
Signed-off-by: Gustavo A. R. Silva <gustavoars at kernel.org>
---
 drivers/mtd/devices/mtd_intel_dg.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mtd/devices/mtd_intel_dg.c b/drivers/mtd/devices/mtd_intel_dg.c
index 2bab30dcd35f..d3e89fe324b8 100644
--- a/drivers/mtd/devices/mtd_intel_dg.c
+++ b/drivers/mtd/devices/mtd_intel_dg.c
@@ -768,6 +768,9 @@ static int intel_dg_mtd_probe(struct auxiliary_device *aux_dev,
 	if (!nvm)
 		return -ENOMEM;
 
+	/* Update nvm->nregions before first access to nvm->regions[] below. */
+	nvm->nregions = nregions;
+
 	kref_init(&nvm->refcnt);
 	mutex_init(&nvm->lock);
 
-- 
2.43.0