[PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split

[Luis Chamberlain]

If the file entry is too long we may easily end up going out of bounds
and crash after strsep() on sscanf(). To avoid this ensure we bound the
string to an expected length before we use sscanf() on it.

Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
 mm/huge_memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9e9879d2f501..8386d24a163e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3623,6 +3623,7 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
 		char file_path[MAX_INPUT_BUF_SZ];
 		pgoff_t off_start = 0, off_end = 0;
 		size_t input_len = strlen(input_buf);
+		size_t max_left_over;
 
 		tok = strsep(&buf, ",");
 		if (tok) {
@@ -3632,6 +3633,14 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
 			goto out;
 		}
 
+		max_left_over = MAX_INPUT_BUF_SZ - strlen(file_path);
+		if (!buf ||
+		    strnlen(buf, max_left_over) < 7 ||
+		    strnlen(buf, max_left_over) > max_left_over) {
+			ret = -EINVAL;
+			goto out;
+		}
+
 		ret = sscanf(buf, "0x%lx,0x%lx,%d", &off_start, &off_end, &new_order);
 		if (ret != 2 && ret != 3) {
 			ret = -EINVAL;
-- 
2.43.0