exec.c

LINUX 1.0 内核c源代码,是一份精简的linux内核源代码

/*
 * This function flushes out all traces of the currently running executable so
 * that a new one can be started
 */

void flush_old_exec(struct linux_binprm * bprm)
{
	int i;
	int ch;
	char * name;
	struct vm_area_struct * mpnt, *mpnt1;

	current->dumpable = 1;
	name = bprm->filename;
	for (i=0; (ch = *(name++)) != '\0';) {
		if (ch == '/')
			i = 0;
		else
			if (i < 15)
				current->comm[i++] = ch;
	}
	current->comm[i] = '\0';
	if (current->shm)
		shm_exit();
	if (current->executable) {
		iput(current->executable);
		current->executable = NULL;
	}
	/* Release all of the old mmap stuff. */

	mpnt = current->mmap;
	current->mmap = NULL;
	current->stk_vma = NULL;
	while (mpnt) {
		mpnt1 = mpnt->vm_next;
		if (mpnt->vm_ops && mpnt->vm_ops->close)
			mpnt->vm_ops->close(mpnt);
		kfree(mpnt);
		mpnt = mpnt1;
	}

	/* Flush the old ldt stuff... */
	if (current->ldt) {
		free_page((unsigned long) current->ldt);
		current->ldt = NULL;
		for (i=1 ; i<NR_TASKS ; i++) {
			if (task[i] == current)  {
				set_ldt_desc(gdt+(i<<1)+
					     FIRST_LDT_ENTRY,&default_ldt, 1);
				load_ldt(i);
			}
		}	
	}

	for (i=0 ; i<8 ; i++) current->debugreg[i] = 0;

	if (bprm->e_uid != current->euid || bprm->e_gid != current->egid || 
	    !permission(bprm->inode,MAY_READ))
		current->dumpable = 0;
	current->signal = 0;
	for (i=0 ; i<32 ; i++) {
		current->sigaction[i].sa_mask = 0;
		current->sigaction[i].sa_flags = 0;
		if (current->sigaction[i].sa_handler != SIG_IGN)
			current->sigaction[i].sa_handler = NULL;
	}
	for (i=0 ; i<NR_OPEN ; i++)
		if (FD_ISSET(i,&current->close_on_exec))
			sys_close(i);
	FD_ZERO(&current->close_on_exec);
	clear_page_tables(current);
	if (last_task_used_math == current)
		last_task_used_math = NULL;
	current->used_math = 0;
	current->elf_executable = 0;
}

/*
 * sys_execve() executes a new program.
 */
static int do_execve(char * filename, char ** argv, char ** envp, struct pt_regs * regs)
{
	struct linux_binprm bprm;
	struct linux_binfmt * fmt;
	unsigned long old_fs;
	int i;
	int retval;
	int sh_bang = 0;

	if (regs->cs != USER_CS)
		return -EINVAL;
	bprm.p = PAGE_SIZE*MAX_ARG_PAGES-4;
	for (i=0 ; i<MAX_ARG_PAGES ; i++)	/* clear page-table */
		bprm.page[i] = 0;
	retval = open_namei(filename, 0, 0, &bprm.inode, NULL);
	if (retval)
		return retval;
	bprm.filename = filename;
	bprm.argc = count(argv);
	bprm.envc = count(envp);
	
restart_interp:
	if (!S_ISREG(bprm.inode->i_mode)) {	/* must be regular file */
		retval = -EACCES;
		goto exec_error2;
	}
	if (IS_NOEXEC(bprm.inode)) {		/* FS mustn't be mounted noexec */
		retval = -EPERM;
		goto exec_error2;
	}
	if (!bprm.inode->i_sb) {
		retval = -EACCES;
		goto exec_error2;
	}
	i = bprm.inode->i_mode;
	if (IS_NOSUID(bprm.inode) && (((i & S_ISUID) && bprm.inode->i_uid != current->
	    euid) || ((i & S_ISGID) && !in_group_p(bprm.inode->i_gid))) &&
	    !suser()) {
		retval = -EPERM;
		goto exec_error2;
	}
	/* make sure we don't let suid, sgid files be ptraced. */
	if (current->flags & PF_PTRACED) {
		bprm.e_uid = current->euid;
		bprm.e_gid = current->egid;
	} else {
		bprm.e_uid = (i & S_ISUID) ? bprm.inode->i_uid : current->euid;
		bprm.e_gid = (i & S_ISGID) ? bprm.inode->i_gid : current->egid;
	}
	if (current->euid == bprm.inode->i_uid)
		i >>= 6;
	else if (in_group_p(bprm.inode->i_gid))
		i >>= 3;
	if (!(i & 1) &&
	    !((bprm.inode->i_mode & 0111) && suser())) {
		retval = -EACCES;
		goto exec_error2;
	}
	memset(bprm.buf,0,sizeof(bprm.buf));
	old_fs = get_fs();
	set_fs(get_ds());
	retval = read_exec(bprm.inode,0,bprm.buf,128);
	set_fs(old_fs);
	if (retval < 0)
		goto exec_error2;
	if ((bprm.buf[0] == '#') && (bprm.buf[1] == '!') && (!sh_bang)) {
		/*
		 * This section does the #! interpretation.
		 * Sorta complicated, but hopefully it will work.  -TYT
		 */

		char *cp, *interp, *i_name, *i_arg;

		iput(bprm.inode);
		bprm.buf[127] = '\0';
		if ((cp = strchr(bprm.buf, '\n')) == NULL)
			cp = bprm.buf+127;
		*cp = '\0';
		while (cp > bprm.buf) {
			cp--;
			if ((*cp == ' ') || (*cp == '\t'))
				*cp = '\0';
			else
				break;
		}
		for (cp = bprm.buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
		if (!cp || *cp == '\0') {
			retval = -ENOEXEC; /* No interpreter name found */
			goto exec_error1;
		}
		interp = i_name = cp;
		i_arg = 0;
		for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++) {
 			if (*cp == '/')
				i_name = cp+1;
		}
		while ((*cp == ' ') || (*cp == '\t'))
			*cp++ = '\0';
		if (*cp)
			i_arg = cp;
		/*
		 * OK, we've parsed out the interpreter name and
		 * (optional) argument.
		 */
		if (sh_bang++ == 0) {
			bprm.p = copy_strings(bprm.envc, envp, bprm.page, bprm.p, 0);
			bprm.p = copy_strings(--bprm.argc, argv+1, bprm.page, bprm.p, 0);
		}
		/*
		 * Splice in (1) the interpreter's name for argv[0]
		 *           (2) (optional) argument to interpreter
		 *           (3) filename of shell script
		 *
		 * This is done in reverse order, because of how the
		 * user environment and arguments are stored.
		 */
		bprm.p = copy_strings(1, &bprm.filename, bprm.page, bprm.p, 2);
		bprm.argc++;
		if (i_arg) {
			bprm.p = copy_strings(1, &i_arg, bprm.page, bprm.p, 2);
			bprm.argc++;
		}
		bprm.p = copy_strings(1, &i_name, bprm.page, bprm.p, 2);
		bprm.argc++;
		if (!bprm.p) {
			retval = -E2BIG;
			goto exec_error1;
		}
		/*
		 * OK, now restart the process with the interpreter's inode.
		 * Note that we use open_namei() as the name is now in kernel
		 * space, and we don't need to copy it.
		 */
		retval = open_namei(interp, 0, 0, &bprm.inode, NULL);
		if (retval)
			goto exec_error1;
		goto restart_interp;
	}
	if (!sh_bang) {
		bprm.p = copy_strings(bprm.envc,envp,bprm.page,bprm.p,0);
		bprm.p = copy_strings(bprm.argc,argv,bprm.page,bprm.p,0);
		if (!bprm.p) {
			retval = -E2BIG;
			goto exec_error2;
		}
	}

	bprm.sh_bang = sh_bang;
	fmt = formats;
	do {
		int (*fn)(struct linux_binprm *, struct pt_regs *) = fmt->load_binary;
		if (!fn)
			break;
		retval = fn(&bprm, regs);
		if (retval == 0) {
			iput(bprm.inode);
			current->did_exec = 1;
			return 0;
		}
		fmt++;
	} while (retval == -ENOEXEC);
exec_error2:
	iput(bprm.inode);
exec_error1:
	for (i=0 ; i<MAX_ARG_PAGES ; i++)
		free_page(bprm.page[i]);
	return(retval);
}

/*
 * sys_execve() executes a new program.
 */
asmlinkage int sys_execve(struct pt_regs regs)
{
	int error;
	char * filename;

	error = getname((char *) regs.ebx, &filename);
	if (error)
		return error;
	error = do_execve(filename, (char **) regs.ecx, (char **) regs.edx, &regs);
	putname(filename);
	return error;
}

/*
 * These are  the prototypes for the  functions in the  dispatch table, as
 * well as the  dispatch  table itself.
 */

extern int load_aout_binary(struct linux_binprm *,
			    struct pt_regs * regs);
extern int load_aout_library(int fd);

#ifdef CONFIG_BINFMT_ELF
extern int load_elf_binary(struct linux_binprm *,
			    struct pt_regs * regs);
extern int load_elf_library(int fd);
#endif

#ifdef CONFIG_BINFMT_COFF
extern int load_coff_binary(struct linux_binprm *,
			    struct pt_regs * regs);
extern int load_coff_library(int fd);
#endif

/* Here are the actual binaries that will be accepted  */
struct linux_binfmt formats[] = {
	{load_aout_binary, load_aout_library},
#ifdef CONFIG_BINFMT_ELF
	{load_elf_binary, load_elf_library},
#endif
#ifdef CONFIG_BINFMT_COFF
	{load_coff_binary, load_coff_library},
#endif
	{NULL, NULL}
};

/*
 * These are the functions used to load a.out style executables and shared
 * libraries.  There is no binary dependent code anywhere else.
 */

int load_aout_binary(struct linux_binprm * bprm, struct pt_regs * regs)
{
	struct exec ex;
	struct file * file;
	int fd, error;
	unsigned long p = bprm->p;

	ex = *((struct exec *) bprm->buf);		/* exec-header */
	if ((N_MAGIC(ex) != ZMAGIC && N_MAGIC(ex) != OMAGIC && 
	     N_MAGIC(ex) != QMAGIC) ||
	    ex.a_trsize || ex.a_drsize ||
	    bprm->inode->i_size < ex.a_text+ex.a_data+ex.a_syms+N_TXTOFF(ex)) {
		return -ENOEXEC;
	}

	if (N_MAGIC(ex) == ZMAGIC &&
	    (N_TXTOFF(ex) < bprm->inode->i_sb->s_blocksize)) {
		printk("N_TXTOFF < BLOCK_SIZE. Please convert binary.");
		return -ENOEXEC;
	}

	if (N_TXTOFF(ex) != BLOCK_SIZE && N_MAGIC(ex) == ZMAGIC) {
		printk("N_TXTOFF != BLOCK_SIZE. See a.out.h.");
		return -ENOEXEC;
	}
	
	/* OK, This is the point of no return */
	flush_old_exec(bprm);

	current->end_code = N_TXTADDR(ex) + ex.a_text;
	current->end_data = ex.a_data + current->end_code;
	current->start_brk = current->brk = current->end_data;
	current->start_code += N_TXTADDR(ex);
	current->rss = 0;
	current->suid = current->euid = bprm->e_uid;
	current->mmap = NULL;
	current->executable = NULL;  /* for OMAGIC files */
	current->sgid = current->egid = bprm->e_gid;
	if (N_MAGIC(ex) == OMAGIC) {
		do_mmap(NULL, 0, ex.a_text+ex.a_data,
			PROT_READ|PROT_WRITE|PROT_EXEC,
			MAP_FIXED|MAP_PRIVATE, 0);
		read_exec(bprm->inode, 32, (char *) 0, ex.a_text+ex.a_data);
	} else {
		if (ex.a_text & 0xfff || ex.a_data & 0xfff)
			printk("%s: executable not page aligned\n", current->comm);
		
		fd = open_inode(bprm->inode, O_RDONLY);
		
		if (fd < 0)
			return fd;
		file = current->filp[fd];
		if (!file->f_op || !file->f_op->mmap) {
			sys_close(fd);
			do_mmap(NULL, 0, ex.a_text+ex.a_data,
				PROT_READ|PROT_WRITE|PROT_EXEC,
				MAP_FIXED|MAP_PRIVATE, 0);
			read_exec(bprm->inode, N_TXTOFF(ex),
				  (char *) N_TXTADDR(ex), ex.a_text+ex.a_data);
			goto beyond_if;
		}
		error = do_mmap(file, N_TXTADDR(ex), ex.a_text,
				PROT_READ | PROT_EXEC,
				MAP_FIXED | MAP_SHARED, N_TXTOFF(ex));

		if (error != N_TXTADDR(ex)) {
			sys_close(fd);
			send_sig(SIGSEGV, current, 0);
			return 0;
		};
		
 		error = do_mmap(file, N_TXTADDR(ex) + ex.a_text, ex.a_data,
				PROT_READ | PROT_WRITE | PROT_EXEC,
				MAP_FIXED | MAP_PRIVATE, N_TXTOFF(ex) + ex.a_text);
		sys_close(fd);
		if (error != N_TXTADDR(ex) + ex.a_text) {
			send_sig(SIGSEGV, current, 0);
			return 0;
		};
		current->executable = bprm->inode;
		bprm->inode->i_count++;
	}
beyond_if:
	sys_brk(current->brk+ex.a_bss);
	
	p += change_ldt(ex.a_text,bprm->page);
	p -= MAX_ARG_PAGES*PAGE_SIZE;
	p = (unsigned long) create_tables((char *)p,bprm->argc,bprm->envc,0);
	current->start_stack = p;
	regs->eip = ex.a_entry;		/* eip, magic happens :-) */
	regs->esp = p;			/* stack pointer */
	if (current->flags & PF_PTRACED)
		send_sig(SIGTRAP, current, 0);
	return 0;
}


int load_aout_library(int fd)
{
        struct file * file;
	struct exec ex;
	struct  inode * inode;
	unsigned int len;
	unsigned int bss;
	unsigned int start_addr;
	int error;
	
	file = current->filp[fd];
	inode = file->f_inode;
	
	set_fs(KERNEL_DS);
	if (file->f_op->read(inode, file, (char *) &ex, sizeof(ex)) != sizeof(ex)) {
		return -EACCES;
	}
	set_fs(USER_DS);
	
	/* We come in here for the regular a.out style of shared libraries */
	if ((N_MAGIC(ex) != ZMAGIC && N_MAGIC(ex) != QMAGIC) || ex.a_trsize ||
	    ex.a_drsize || ((ex.a_entry & 0xfff) && N_MAGIC(ex) == ZMAGIC) ||
	    inode->i_size < ex.a_text+ex.a_data+ex.a_syms+N_TXTOFF(ex)) {
		return -ENOEXEC;
	}
	if (N_MAGIC(ex) == ZMAGIC && N_TXTOFF(ex) && 
	    (N_TXTOFF(ex) < inode->i_sb->s_blocksize)) {
		printk("N_TXTOFF < BLOCK_SIZE. Please convert library\n");
		return -ENOEXEC;
	}
	
	if (N_FLAGS(ex)) return -ENOEXEC;

	/* For  QMAGIC, the starting address is 0x20 into the page.  We mask
	   this off to get the starting address for the page */

	start_addr =  ex.a_entry & 0xfffff000;

	/* Now use mmap to map the library into memory. */
	error = do_mmap(file, start_addr, ex.a_text + ex.a_data,
			PROT_READ | PROT_WRITE | PROT_EXEC, MAP_FIXED | MAP_PRIVATE,
			N_TXTOFF(ex));
	if (error != start_addr)
		return error;
	len = PAGE_ALIGN(ex.a_text + ex.a_data);
	bss = ex.a_text + ex.a_data + ex.a_bss;
	if (bss > len)
		do_mmap(NULL, start_addr + len, bss-len,
			PROT_READ|PROT_WRITE|PROT_EXEC,
			MAP_PRIVATE|MAP_FIXED, 0);
	return 0;
}