of: module: add buffer overflow check in of_modalias()

In of_modalias(), if the buffer happens to be too small even for the 1st
snprintf() call, the len parameter will become negative and str parameter
(if not NULL initially) will point beyond the buffer's end. Add the buffer
overflow check after the 1st snprintf() call and fix such check after the
strlen() call (accounting for the terminating NUL char).

Fixes: bc575064d688 ("of/device: use of_property_for_each_string to parse compatible strings")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/bbfc6be0-c687-62b6-d015-5141b93f313e@omp.ru
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/drivers/of/module.c b/drivers/of/module.c
index 0e8aa974f0f2bb5262dfbc8b03978b6381bfd61e..6c2c3e91f7ed88be3c3be3dab82fa40d9ec178bf 100644 (file)
--- a/drivers/of/module.c
+++ b/drivers/of/module.c
@@ -21,14 +21,15 @@ ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
        csize = snprintf(str, len, "of:N%pOFn%c%s", np, 'T',
                         of_node_get_device_type(np));
        tsize = csize;
+       if (csize >= len)
+               csize = len > 0 ? len - 1 : 0;
        len -= csize;
-       if (str)
-               str += csize;
+       str += csize;
 
        of_property_for_each_string(np, "compatible", p, compat) {
                csize = strlen(compat) + 1;
                tsize += csize;
-               if (csize > len)
+               if (csize >= len)
                        continue;
 
                csize = snprintf(str, len, "C%s", compat);