[PATCH v2 02/10] soundwire: sysfs: Use sysfs_emit_at() in array show callbacks

[Lee Jones]

words_show() and the show callbacks generated by sdw_dpn_array_attr()
format firmware-supplied property arrays into the sysfs buffer using
unbounded sprintf(buf + size, ...) loops.  If firmware provides a large
array count, sprintf() can write past PAGE_SIZE and corrupt kernel
memory.

Replace the sprintf(buf + size, ...) calls with bounds-checked
sysfs_emit_at() calls.

Closes: https://sashiko.dev/#/bug/linux-543ff498-3bed-412d-8972-4855c5aa6008
Signed-off-by: Lee Jones <lee@xxxxxxxxxx>
---

v1 => v2: Drop Fixes and Stable tags

 drivers/soundwire/sysfs_slave.c     | 6 +++---
 drivers/soundwire/sysfs_slave_dpn.c | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/soundwire/sysfs_slave.c b/drivers/soundwire/sysfs_slave.c
index a2ee064147e0..35272cfe9fc8 100644
--- a/drivers/soundwire/sysfs_slave.c
+++ b/drivers/soundwire/sysfs_slave.c
@@ -161,9 +161,9 @@ static ssize_t words_show(struct device *dev,
 	int i;
 
 	for (i = 0; i < slave->prop.dp0_prop->num_words; i++)
-		size += sprintf(buf + size, "%d ",
-				slave->prop.dp0_prop->words[i]);
-	size += sprintf(buf + size, "\n");
+		size += sysfs_emit_at(buf, size, "%d ",
+				      slave->prop.dp0_prop->words[i]);
+	size += sysfs_emit_at(buf, size, "\n");
 
 	return size;
 }
diff --git a/drivers/soundwire/sysfs_slave_dpn.c b/drivers/soundwire/sysfs_slave_dpn.c
index d2561400da77..16872ea64b1f 100644
--- a/drivers/soundwire/sysfs_slave_dpn.c
+++ b/drivers/soundwire/sysfs_slave_dpn.c
@@ -134,10 +134,10 @@ static ssize_t field##_dpn_show(struct sdw_slave *slave,		\
 	for_each_set_bit(bit, &mask, 32) {				\
 		if (bit == N) {						\
 			for (j = 0; j < dpn[i].num_##field; j++)	\
-				size += sprintf(buf + size,		\
-						format_string,		\
-						dpn[i].field[j]);	\
-			size += sprintf(buf + size, "\n");		\
+				size += sysfs_emit_at(buf, size,	\
+						      format_string,	\
+						      dpn[i].field[j]);	\
+			size += sysfs_emit_at(buf, size, "\n");		\
 			return size;					\
 		}							\
 		i++;							\
-- 
2.56.0.385.gac671c819a-goog