Re: [PATCH v3 1/2] vsprintf: Add %p[mM]U for uppercase MAC address

Hello Rasmus, Konrad, *,

On Thu, 27 Apr 2023 14:35:19 +0200, Rasmus Villemoes linux@rasmusvillemoes.dk wrote:

On 27/04/2023 13.51, Konrad Gräfe wrote:

...

The CDC-ECM specification requires an USB gadget to send the host MAC address as uppercase hex string. This change adds the appropriate modifier.

Cc: stable@vger.kernel.org

Why cc stable?

...

Signed-off-by: Konrad Gräfe k.graefe@gateware.de

Added in v3

lib/vsprintf.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)

The diffstat here, or for some other patch in the same series, definitely ought to mention lib/test_printf.c.

...

diff --git a/lib/vsprintf.c b/lib/vsprintf.c index be71a03c936a..8aee1caabd9e 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1269,9 +1269,10 @@ char *mac_address_string(char *buf, char *end, u8 *addr, { char mac_addr[sizeof("xx:xx:xx:xx:xx:xx")]; char *p = mac_addr;

• int i;

• int i, pos; char separator; bool reversed = false;
• bool uppercase = false;

if (check_pointer(&buf, end, addr, spec)) return buf; @@ -1281,6 +1282,10 @@ char *mac_address_string(char *buf, char *end, u8 *addr, separator = '-'; break;

• case 'U':

• uppercase = true;
  

• break;
  

• case 'R': reversed = true; fallthrough;

This seems broken, and I'm surprised the compiler doesn't warn about separator possibly being uninitialized further down. I'm also surprised your testing hasn't caught this. For reference, the full switch statement is currently

Compiler (gcc) does not warn because of Makefile:

1038 # Enabled with W=2, disabled by default as noisy 1039 ifdef CONFIG_CC_IS_GCC 1040 KBUILD_CFLAGS += -Wno-maybe-uninitialized 1041 endif

With this commented:

lib/vsprintf.c: In function ‘mac_address_string’: lib/vsprintf.c:1310:30: warning: ‘separator’ may be used uninitialized [-Wmaybe-uninitialized] 1310 | *p++ = separator; | ~~~~~^~~~~~~~~~~ lib/vsprintf.c:1273:14: note: ‘separator’ was declared here 1273 | char separator; | ^~~~~~~~~

Regards, Peter

    switch (fmt[1]) {
    case 'F':
            separator = '-';
            break;

    case 'R':
            reversed = true;
            fallthrough;

    default:
            separator = ':';
            break;
    }

...

@@ -1292,9 +1297,14 @@ char *mac_address_string(char *buf, char *end, u8 *addr, for (i = 0; i < 6; i++) { if (reversed)

• 	p = hex_byte_pack(p, addr[5 - i]);
  

• 	pos = 5 - i;
  

• else
  

• 	pos = i;
  

• if (uppercase)
  

• 	p = hex_byte_pack_upper(p, addr[pos]);
  

  else

• 	p = hex_byte_pack(p, addr[i]);
  

• 	p = hex_byte_pack(p, addr[pos]);  
  

I think this becomes quite hard to follow. We have string_upper() in linux/string_helpers.h, so I'd rather just leave this loop alone and do

if (uppercase) string_upper(mac_addr, mac_addr);

after the nul-termination.

Rasmus