Hi,
For my research, I am now hooking the function vn_write().
This is the part of the source code.
#include sys/param.h/* module */
#include sys/module.h /* module */
#include sys/kernel.h /* module */
#include sys/types.h/* size_t, copystr */
#include sys/systm.h/* copystr */
#include sys/proc.h /* struct thread*/
#include sys/file.h /* vnops*/
#include fs/msdosfs/msdosfs_vnops.c /* msdosfs_vnodeops */
int
fo_write_hook(struct file *fp,
struct uio *uio,
struct ucred *active_cred,
int flags,
struct thread *td);
typedef int (*fow_t)(struct file*,
struct uio*,
struct ucred*,
int flags,
struct thread*);
fow_t old_fo_write;
static char mybuf[256+1];
static size_t len;
/* vn_write hook */
int
vn_write_hook(struct file *fp,
struct uio *uio,
struct ucred *active_cred,
int flags,
struct thread *td)
{
...
int error;
memset(mybuf, '\0', 257);
error = copyinstr(uio-uio_iov-iov_base, mybuf, 256, len);
if (error != 0) {
uprintf(Cannot write data to kernel space\n);
}
/* encrypt the data by ceaser algorithm */
for (int i = 0; i len ; i++)
mybuf[i] += 3;
error = copystr(mybuf, uio-uio_iov-iov_base, 257, len);
if (error != 0) {
uprintf(Cannot write data to user space\n);
}
...
return (old_vn_write(fp, uio, active_cred, flags, td));
}
This software is implemented as a kernel module.
After I installed this software and execute cp command, vn_write_hook
function is executed.
However, when copystr(mybuf, uio-uio_iov-iov_base, 257, len) is
executed,
kernel goes to panic.
I referenced /usr/share/examples/kld/cdev/module/cdev.c for writing the
part of program
that copies buffer in kernel space to a buf in user space program.
However, as we have seen,
this doesn't work appropriately.
How can I solve this problem?
Please give me your help.
--Jun Furukawa
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