Programming

struct file *fp;
/* ... */
fp = filp_open("some/file/on/my/pc", O_RDONLY, 0);
if(fp == NULL) {
     ALERT("NULLPOINTER"); // predefinied makro for output
     return;
}
if(fp->f_dentry == NULL) {
     ALERT("NULLPOINTER"); 
     return;
}
printk(KERN_INFO "Filname: %\n", fp->f_dentry->d_name.name);

[  967.249027] BUG: unable to handle kernel NULL pointer dereference at 0000000a
[  967.249032] IP: [<f086c147>] openFile+0x57/0x1a8 [elfreader]
[  967.249044] *pde = 205ca067 *pte = 00000000 
[  967.249048] Oops: 0000 [#1] SMP

[  967.249032] IP: [<f086c147>] openFile+0x57/0x1a8 [elfreader]

void openFile(void) {
    char *buf;
    int size;
    struct elfhdr elfH;
    Elf32_Shdr *elfSec;
    struct file *fp;
    fp = filp_open("/home/chris/Test/test", O_RDONLY, 0);
        
    if(fp == (void *)0L) {
        PRINT("FILE NICHT DA");
        return;
    }

    if(fp->f_dentry == (void *)0L) {
        PRINT("F_DENTRY NICHT DA");
        return;
    }

    if(!fp->f_dentry->d_name.name) {
        PRINT("F_DENTRY NICHT DA");
        return;
    }
    
    printk(KERN_INFO "FILENAME: %s\n", fp->f_dentry->d_name.name);
    
    if(!(buf = kmalloc(BINPRM_BUF_SIZE, GFP_KERNEL))) {
        PRINT("KMALLOC");
        return;
    }

    kernel_read(fp, 0, buf, BINPRM_BUF_SIZE);
    elfH = *((struct elfhdr *) buf);

    size = elfH.e_shnum * sizeof(Elf32_Shdr);
    if(!(elfSec = (Elf32_Shdr *) kmalloc(size, GFP_KERNEL))) {
        PRINT("KMALLOC2");
        kfree(buf);
        return;
    }

    readElf(&elfH, elfSec); // another function, works fine when we get here
    kfree(elfSec);
}