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

[ Upstream commit cf7385cb26ac4f0ee6c7385960525ad534323252 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/of/module.c b/drivers/of/module.c
index f58e624953a20f25f058841b70eb9468d6f5d11e..780fd82a7ecc58c796fccba37883aa938481eb69 100644 (file)
--- a/drivers/of/module.c
+++ b/drivers/of/module.c
@@ -29,14 +29,15 @@ 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);