kernfs: Fix range checks in kernfs_get_target_path

The terminating NUL byte is only there because the buffer is allocated with kzalloc(PAGE_SIZE, GFP_KERNEL), but since the range-check is off-by-one, and PAGE_SIZE==PATH_MAX, the returned string may not be zero-terminated if it is exactly PATH_MAX characters long. Furthermore also the initial loop may theoretically exceed PATH_MAX and cause a fault. Signed-off-by: Bernd Edlinger <[email protected]> Acked-by: Tejun Heo <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
chewitt · Sep 16, 2018 · a75e78f · a75e78f
1 parent bdae566
commit a75e78f
Showing 1 changed file with 4 additions and 1 deletion.
diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
@@ -72,6 +72,9 @@ static int kernfs_get_target_path(struct kernfs_node *parent,
 		if (base == kn)
 			break;
 
+		if ((s - path) + 3 >= PATH_MAX)
+			return -ENAMETOOLONG;
+
 		strcpy(s, "../");
 		s += 3;
 		base = base->parent;
@@ -88,7 +91,7 @@ static int kernfs_get_target_path(struct kernfs_node *parent,
 	if (len < 2)
 		return -EINVAL;
 	len--;
-	if ((s - path) + len > PATH_MAX)
+	if ((s - path) + len >= PATH_MAX)
 		return -ENAMETOOLONG;
 
 	/* reverse fillup of target string from target to base */