[PATCH] USB: Fix NULLPTR dereference when serial# is unset

[Michael]

The problem can be reproduced with U-Boot's sandbox with the default config.
Then, run the following commands at the shell:
Hit any key to stop autoboot:  0
=> env set serial# test
=> env default -f serial#
at which point the program will crash.

The following change will show that the env default -f command causes
the null pointer dereference

 void g_dnl_set_serialnumber(char *s)
 {
        memset(g_dnl_serial, 0, MAX_STRING_SERIAL);
+       printf("Reading serial from address %p\n", s);
        strncpy(g_dnl_serial, s, MAX_STRING_SERIAL - 1);
 }

On Mon, Jan 27, 2025 at 3:58 PM Marek Vasut <marex at denx.de> wrote:
>
> On 1/27/25 10:07 PM, Michael Ferolito wrote:
> > The current behaviour of this function will dereference a null pointer
> > if the serial# environment variable is unset. This was discovered on a
> > board where U-Boot did not have access to the first 256MB of ram,
> > resulting in a board crash.
> > In the event that U-Boot has full access to memory, it will still read
> > from address 0, which is probably not optimal.
> > This simple check is enough to fix it.
> How does one trigger this problem ?