[RFC PATCH 1/1] lib/vsprintf: Limit the returning size to INT_MAX

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

There seems a design flaw of vsnprintf() whose return value can
overflow the INT_MAX even on 32bit arch, because the buffer size is
passed by 'size_t' but it returns the printed or required size in 'int'.

The size_t is unsigned long, thus the caller can pass bigger than INT_MAX
as the size of buffer (that is OK). But even the vsnprintf calculates
the required/printed length correctly, if it overflows the INT_MAX,
it can not return the size correctly by int.

This should never happen but it should be checked and limited.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 drivers/firmware/efi/libstub/vsprintf.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/vsprintf.c b/drivers/firmware/efi/libstub/vsprintf.c
index 71c71c222346..1713cacecc25 100644
--- a/drivers/firmware/efi/libstub/vsprintf.c
+++ b/drivers/firmware/efi/libstub/vsprintf.c
@@ -549,7 +549,7 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list ap)
 	if (size)
 		buf[min(pos, size-1)] = '\0';
 
-	return pos;
+	return (pos > INT_MAX) ? INT_MAX : pos;
 }
 
 int snprintf(char *buf, size_t size, const char *fmt, ...)