efi/printf: Turn vsprintf into vsnprintf

Implement vsnprintf instead of vsprintf to avoid the possibility of a
buffer overflow.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200518190716.751506-17-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 56b3b84fd3bd..5ecafc57619a 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -60,10 +60,14 @@ int efi_printk(const char *fmt, ...)
 	int printed;
 
 	va_start(args, fmt);
-	printed = vsprintf(printf_buf, fmt, args);
+	printed = vsnprintf(printf_buf, sizeof(printf_buf), fmt, args);
 	va_end(args);
 
 	efi_puts(printf_buf);
+	if (printed >= sizeof(printf_buf)) {
+		efi_puts("[Message truncated]\n");
+		return -1;
+	}
 
 	return printed;
 }