Dang, I sent this a little too early... I meant to point out that the
read() call is returning -14, which I believe is EFAULT. I think the
reason for the kernel exception is that I pass that blindly to the
hash update call.
The root of the problem appears to be the read call, but I don't
understand what I am doing wrong there.
rjf&
On 6/2/05, rjf <itripn@private> wrote:
> This may border on off topic, and I would be pleased to be pointed
> elsewhere if so...
>
> I am attempting to write an lsm that hashes as part of the
> bprm_check_security hook. The trouble I am having is trying to read
> and hash the file. I have successfully used the kernel crytpo code to
> hash a static buffer, to make sure I understood its usage, and have
> now moved on to actually trying to open and read the file being passed
> to the hook. My module causes a kernel exception with this message in
> the syslog:
>
> Jun 2 09:36:36 foo Unable to handle kernel paging request at virtual
> address c6000000
>
> I'll be the first to admit I don't know what the hell I am doing, as
> this is my first foray into kernel code. Below is the code for the
> helper function in question, which is being called like so from the
> hook:
>
> hashFile(bprm->filename, "sha1", bprm->file );
>
> And the helper function:
>
> static void hashFile(char *filename, char *algo, struct file *file) {
>
> struct scatterlist sg[1];
> char result[64];
> struct crypto_tfm *tfm;
>
> // alloc a buffer
> void *m = kmalloc(1024, GFP_KERNEL);
> if ( !m ) {
> printk("failed to alloc buffer...\n");
> return;
> }
>
> // init crypto
> tfm = crypto_alloc_tfm(algo, 0);
> if (tfm == NULL) {
> printk("failed to load transform for %s\n", algo);
> return;
> }
> crypto_digest_init (tfm);
>
> // init scatterlist -- the first two fields shouldn't change
> // since we read into the same buffer each time.
> sg[0].page = virt_to_page (m);
> sg[0].offset = offset_in_page (m);
> sg[0].length = 0;
>
> // loop reading the file a buffer at a time, updating the hash.
> int bytesRead = 0;
> int ret = file->f_op->open( file->f_mapping->host, file );
> if ( ret == 0 ) {
> do {
>
> bytesRead = file->f_op->read(file, m, 1024, &file->f_pos);
> sg[0].length = bytesRead;
> crypto_digest_update (tfm, sg, 1);
>
> } while (bytesRead == 1024);
>
> // cleanup
> file->f_op->release(file->f_mapping->host, file);
> crypto_digest_final(tfm, result);
>
> // log the hash to the syslog
> hexdump(filename, result, crypto_tfm_alg_digestsize (tfm));
> }
> else
> printk("failed to open file: %s (%d)\n", filename, ret);
>
> kfree(m);
> }
>
>
> Thanks,
> --
> rjf&
>
--
rjf&
This archive was generated by hypermail 2.1.3 : Thu Jun 02 2005 - 20:27:43 PDT