Hi all,
I developed an LKM and loaded it into android emulator. At first, I
called filp_open("/data/", O_RDONLY, 0) from kernel module init
function (called during insmod). The function filp_open() ran
successfully. Then, I wrote ioctl(), to command kernel module from
usermode, but filp_open("/data/", O_RDONLY, 0) here is failing on
directory "/data/", and returned -13 (permission denied) error.
However, flip_open() on full filepath, say "/data/data/
com.android.music/shared_prefs/Music.xml" ran successfully.
I am not able to understand why this error came when filp_open() is
called inside dev_ioctl(), but ran successfully when called inside
kernel module init function. Please go through the code attached
below, and help me resolve this error.
test.c (user-mode code)
^^^^^^^^^^^^^^^^^^^^^^^
void Java_com_example_test_TestingJNI( JNIEnv* env, jobject thiz )
{
char buf[256];
fd = open ("/dev/mydev", O_RDONLY);
if (fd > 0 ) {
strcpy (buf, "/data/");
ioctl (fd, IOCTL_CMD, buf);
close (fd);
}
}
driver.c (Kernel-mode code)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
int dev_ioctl(struct inode *Inode, struct file *filp, unsigned int
cmd, char* ubuffer )
{
char dirname[250];
switch (cmd) {
case IOCTL_CMD:
mm_segment_t old_fs = get_fs();
set_fs(KERNEL_DS);
memset (dirname, 0, 250);
if(copy_from_user(dirname, ubuffer, 250))
return -EFAULT;
struct file *filp = filp_open(dirname, O_RDONLY, 0);
if (IS_ERR(filp) || (filp==NULL)) {
printk("filp_open returned error %ld\n",
PTR_ERR(filp));
} else {
printk ("flip_open success\n");
filp_close(filp);
}
set_fs(old_fs);
break;
default:
return -ENOTTY;
};
return 0;
}
Thanks & Regards
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