MIPS: mm: Fix out-of-bounds write in maar_res_walk()

[ Upstream commit 1b001b1 ]

maar_res_walk() uses wi->num_cfg as the index into the fixed-size
wi->cfg array, but checks whether the array is full only after it has
filled the selected entry. If walk_system_ram_range() reports more than
16 memory ranges, the overflow call writes one struct maar_config past
the end of the array before WARN_ON() prevents num_cfg from advancing.

Move the full-array check before taking the array slot and return non-zero
when the scratch array is full, so walk_system_ram_range() terminates the
walk instead of invoking the callback for further ranges.

Fixes: a5718fe ("MIPS: mm: Drop boot_mem_map")

Signed-off-by: Yadan Fan <ydfan@suse.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: yadan-fan

arch/mips/mm/init.c

@@ -281,9 +281,15 @@ static int maar_res_walk(unsigned long start_pfn, unsigned long nr_pages,
 			 void *data)
 {
 	struct maar_walk_info *wi = data;
-	struct maar_config *cfg = &wi->cfg[wi->num_cfg];
+	struct maar_config *cfg;
 	unsigned int maar_align;
 
+	/* Ensure we don't overflow the cfg array */
+	if (WARN_ON(wi->num_cfg >= ARRAY_SIZE(wi->cfg)))
+		return -1;
+
+	cfg = &wi->cfg[wi->num_cfg];
+
 	/* MAAR registers hold physical addresses right shifted by 4 bits */
 	maar_align = BIT(MIPS_MAAR_ADDR_SHIFT + 4);
 
@@ -292,9 +298,7 @@ static int maar_res_walk(unsigned long start_pfn, unsigned long nr_pages,
 	cfg->upper = ALIGN_DOWN(PFN_PHYS(start_pfn + nr_pages), maar_align) - 1;
 	cfg->attrs = MIPS_MAAR_S;
 
-	/* Ensure we don't overflow the cfg array */
-	if (!WARN_ON(wi->num_cfg >= ARRAY_SIZE(wi->cfg)))
-		wi->num_cfg++;
+	wi->num_cfg++;
 
 	return 0;
 }