[PATCH v1 3/4] powerpc/pseries: energy: bound H_BEST_ENERGY cnt and sysfs output

The H_BEST_ENERGY sysfs path takes cnt from the hypercall return buffer
and walks buf_page[2*i+1] without checking that cnt fits in the single
page allocated for the hcall, and sprintf()s into the PAGE_SIZE sysfs
buffer without remaining-space checks.

Clamp cnt to the number of u32 pairs that fit in the page, and stop
formatting before overflowing the sysfs page.

Signed-off-by: Xixin Liu <[email protected]>
---
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/pseries_energy.c b/arch/powerpc/platforms/pseries/pseries_energy.c
index fdaf85ecd39b..8344f00656e5 100644
--- a/arch/powerpc/platforms/pseries/pseries_energy.c
+++ b/arch/powerpc/platforms/pseries/pseries_energy.c
@@ -209,16 +209,28 @@
 		return -EINVAL;
 	}
 
+	/*
+	 * Each entry occupies two u32s in buf_page. Never walk past the
+	 * page, and never sprintf past the PAGE_SIZE sysfs buffer.
+	 */
 	cnt = retbuf[0];
+	if (cnt > (PAGE_SIZE / sizeof(u32)) / 2)
+		cnt = (PAGE_SIZE / sizeof(u32)) / 2;
+
 	for (i = 0; i < cnt; i++) {
 		cpu = drc_index_to_cpu(buf_page[2*i+1]);
 		if ((cpu_online(cpu) && !activate) ||
-		    (!cpu_online(cpu) && activate))
+		    (!cpu_online(cpu) && activate)) {
+			if (s - page >= PAGE_SIZE - 16)
+				break;
 			s += sprintf(s, "%d,", cpu);
+		}
 	}
 	if (s > page) { /* Something to show */
 		s--; /* Suppress last comma */
-		s += sprintf(s, "\n");
+		/* sprintf needs room for '\n' and trailing NUL. */
+		if (s - page < PAGE_SIZE - 1)
+			s += sprintf(s, "\n");
 	}
 
 	free_page((unsigned long) buf_page);
-- 
2.43.0