s390-tools/s390-tools-sles15sp2-02-zipl-libc-Fix-potential-buffer-overflow-in-printf.patch

Subject: [PATCH] [BZ 184060] zipl/libc: Fix potential buffer overflow in printf
From: Philipp Rudo <prudo@linux.ibm.com>

Description:   zipl/libc: Fix potential buffer overflow in printf
Symptom:       Crash of the zipl boot loader during boot.
Problem:       The zipl boot loaders have their own minimalistic libc
               implementation. In it printf and sprintf use vsprintf for string
               formatting. Per definition vsprintf assumes that the buffer it
               writes to is large enough to contain the formatted string and
               performs no size checks. This is problematic for the boot
               loaders because the buffer they use are often allocated on the
               stack. Thus even small changes to the string format can
               potentially cause buffer overflows on the stack.
Solution:      Implement vsnprintf and make use of it.
Reproduction:  Use printf to print a string with >81 characters (exact number
               depends on the stack layout/compiler used).
Upstream-ID:   8874b908254c47c8a6fd7a1aca2c7371c11035c4
Problem-ID:    184060

Upstream-Description:

              zipl/libc: Fix potential buffer overflow in printf

              Per definition vsprint assumes that the provided buffer it writes to is
              large enough to contain the formatted string. As printf uses a fixed
              sized buffer (81 bytes) and has no size checks the use of vsprintf can
              easily cause buffer overflows. Protect against these buffer overflows by
              using vsnprintf instead.

              While at it fix a typo in the comment.

              Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
              Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
              Reviewed-by: Marc Hartmayer <mhartmay@linux.ibm.com>
              Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
              Signed-off-by: Jan Hoeppner <hoeppner@linux.ibm.com>


Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
---
 zipl/boot/libc.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/zipl/boot/libc.c
+++ b/zipl/boot/libc.c
@@ -530,7 +530,7 @@ void sprintf(char *str, const char *fmt,
 }
 
 /*
- * Print formated string
+ * Print formatted string to console
  */
 void printf(const char *fmt, ...)
 {
@@ -538,7 +538,7 @@ void printf(const char *fmt, ...)
 	va_list va;
 
 	va_start(va, fmt);
-	vsprintf(buf, fmt, va);
+	vsnprintf(buf, sizeof(buf), fmt, va);
 	sclp_print(buf);
 	va_end(va);
 }