[Bug 214711] Information leak from kernel to user space in scsi_ioctl.c

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=214711

--- Comment #3 from Andrew Bao (bao00065@umn.edu) ---
Hi Bart,
Yes, It is an information leak.

"my understanding of the C standard is that a compiler is required to
zero-initialize members that have not been mentioned in an initializer list.
From the ANSI C 202x d"raft: "The initialization shall occur in initializer
list order, each initializer provided for a particular subobject overriding any
previously listed initializer for the same subobject; all subobjects that are
not
initialized explicitly shall be initialized implicitly the same as objects that
have static storage duration."

I am wondering in what condition the compiler will zero-initialize the field in
a struct. And what is the initializer in the context? Let say we have a struct
foo:

struct foo{
       int  a;
       int b;
       int c;
};
method 1:

struct foo f; 
f.a = 1;
f.b = 2;

In method 1, will the compiler zero-initialize the field f.c?

method 2:
struct foo f = {
                        .a      =   1
                        .b      =   2

                };
In method 2, will the compiler zero-initialize the field f.c?


By the way,
struct compat_cdrom_generic_command {
        unsigned char   cmd[CDROM_PACKET_SIZE];
        compat_caddr_t  buffer;
        compat_uint_t   buflen;
        compat_int_t    stat;
        compat_caddr_t  sense;
        unsigned char   data_direction;
        unsigned char   pad[3];
        compat_int_t    quiet;
        compat_int_t    timeout;
        compat_caddr_t  unused;
};
If this struct does not declare unsigned char pad[3] in order to fill with
padding, will the compiler zero-initialize 3 bytes holes for this struct?

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