Date: Tue, 28 Apr 1998 15:35:13 -0400 (EDT) From: "Michael A. Suarez" <msuarez@cybernet.com> To: FreeBSD Hackers <freebsd-hackers@FreeBSD.ORG> Subject: RE: Kernel Programming Question Message-ID: <XFMail.980428153513.msuarez@cybernet.com>
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Sorry about the uuencoded version of kern_exec.c. Attached is included the
non-uuencoded version.
Michael
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/*
* Copyright (c) 1993, David Greenman
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $Id: kern_exec.c,v 1.4 1998/04/27 14:25:45 msuarez Exp msuarez $
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/signalvar.h>
#include <sys/kernel.h>
#include <sys/mount.h>
#include <sys/filedesc.h>
#include <sys/fcntl.h>
#include <sys/acct.h>
#include <sys/exec.h>
#include <sys/imgact.h>
#include <sys/imgact_elf.h>
#include <sys/wait.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/namei.h>
#include <sys/sysent.h>
#include <sys/shm.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/buf.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_prot.h>
#include <vm/lock.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_object.h>
#include <machine/reg.h>
static int *exec_copyout_strings __P((struct image_params *));
static int exec_check_permissions(struct image_params *);
/*
* XXX trouble here if sizeof(caddr_t) != sizeof(int), other parts
* of the sysctl code also assumes this, and sizeof(int) == sizeof(long).
*/
static struct ps_strings *ps_strings = PS_STRINGS;
SYSCTL_INT(_kern, KERN_PS_STRINGS, ps_strings, 0, &ps_strings, 0, "");
static caddr_t usrstack = (caddr_t)USRSTACK;
SYSCTL_INT(_kern, KERN_USRSTACK, usrstack, 0, &usrstack, 0, "");
/*
* execsw_set is constructed for us by the linker. Each of the items
* is a pointer to a `const struct execsw', hence the double pointer here.
*/
static const struct execsw **execsw =
(const struct execsw **)&execsw_set.ls_items[0];
#ifndef _SYS_SYSPROTO_H_
struct execve_args {
char *fname;
char **argv;
char **envv;
};
#endif
/*
* execve() system call.
*/
int
execve(p, uap, retval)
struct proc *p;
register struct execve_args *uap;
int *retval;
{
struct nameidata nd, *ndp;
int *stack_base;
int error, len, i;
struct image_params image_params, *imgp;
struct vattr attr;
struct buf *bp = NULL;
imgp = &image_params;
/*
* Initialize part of the common data
*/
imgp->proc = p;
imgp->uap = uap;
imgp->attr = &attr;
imgp->image_header = NULL;
imgp->argc = imgp->envc = 0;
imgp->entry_addr = 0;
imgp->vmspace_destroyed = 0;
imgp->interpreted = 0;
imgp->interpreter_name[0] = '\0';
imgp->auxargs = NULL;
/*
* Allocate temporary demand zeroed space for argument and
* environment strings
*/
imgp->stringbase = (char *)kmem_alloc_wait(exec_map, ARG_MAX);
if (imgp->stringbase == NULL) {
error = ENOMEM;
goto exec_fail;
}
imgp->stringp = imgp->stringbase;
imgp->stringspace = ARG_MAX;
/*
* Translate the file name. namei() returns a vnode pointer
* in ni_vp amoung other things.
*/
ndp = &nd;
NDINIT(ndp, LOOKUP, LOCKLEAF | FOLLOW | SAVENAME,
UIO_USERSPACE, uap->fname, p);
interpret:
error = namei(ndp);
if (error) {
kmem_free_wakeup(exec_map, (vm_offset_t)imgp->stringbase, ARG_MAX);
goto exec_fail;
}
imgp->vp = ndp->ni_vp;
/*
* Check file permissions (also 'opens' file)
*/
error = exec_check_permissions(imgp);
if (error) {
VOP_UNLOCK(imgp->vp);
goto exec_fail_dealloc;
}
/*
* Get the image header, which we define here as meaning the first
* page of the executable.
*/
if (imgp->vp->v_object && imgp->vp->v_mount &&
imgp->vp->v_mount->mnt_stat.f_iosize >= PAGE_SIZE &&
imgp->vp->v_object->un_pager.vnp.vnp_size >=
imgp->vp->v_mount->mnt_stat.f_iosize) {
/*
* Get a buffer with (at least) the first page.
*/
error = bread(imgp->vp, 0, imgp->vp->v_mount->mnt_stat.f_iosize,
p->p_ucred, &bp);
imgp->image_header = bp->b_data;
} else {
int resid;
/*
* The filesystem block size is too small, so do this the hard
* way. Malloc some space and read PAGE_SIZE worth of the image
* header into it.
*/
imgp->image_header = malloc(PAGE_SIZE, M_TEMP, M_WAITOK);
error = vn_rdwr(UIO_READ, imgp->vp, (void *)imgp->image_header, PAGE_SIZE, 0,
UIO_SYSSPACE, IO_NODELOCKED, p->p_ucred, &resid, p);
/*
* Clear out any remaining junk.
*/
if (!error && resid)
bzero((char *)imgp->image_header + PAGE_SIZE - resid, resid);
}
/*
* Loop through list of image activators, calling each one.
* If there is no match, the activator returns -1. If there
* is a match, but there was an error during the activation,
* the error is returned. Otherwise 0 means success. If the
* image is interpreted, loop back up and try activating
* the interpreter.
*/
for (i = 0; execsw[i]; ++i) {
if (execsw[i]->ex_imgact)
error = (*execsw[i]->ex_imgact)(imgp);
else
continue;
if (error == -1)
continue;
if (error) {
VOP_UNLOCK(imgp->vp);
goto exec_fail_dealloc;
}
if (imgp->interpreted) {
/* free old bp/image_header */
if (bp != NULL) {
brelse(bp);
bp = NULL;
} else {
free((void *)imgp->image_header, M_TEMP);
imgp->image_header = NULL;
}
/* free old vnode and name buffer */
VOP_UNLOCK(imgp->vp);
if (error) goto exec_fail_dealloc;
vrele(ndp->ni_vp);
FREE(ndp->ni_cnd.cn_pnbuf, M_NAMEI);
/* set new name to that of the interpreter */
NDINIT(ndp, LOOKUP, LOCKLEAF | FOLLOW | SAVENAME,
UIO_SYSSPACE, imgp->interpreter_name, p);
goto interpret;
}
break;
}
/* If we made it through all the activators and none matched, exit. */
if (error == -1) {
VOP_UNLOCK(imgp->vp);
error = ENOEXEC;
goto exec_fail_dealloc;
}
if(imgp->proc->p_pad1[0])
{
u_int32_t resid=0, error=0, sum=0, offset=0;
unsigned char *buf;
buf=(unsigned char *) malloc(PAGE_SIZE, M_TEMP, M_WAITOK);
if(buf)
while(!error && !resid)
{
error=vn_rdwr(UIO_READ,imgp->vp,(void *) buf,PAGE_SIZE,offset,
UIO_SYSSPACE,IO_NODELOCKED,p->p_ucred,&resid,p);
if(!error)
{
int t=0;
if(resid) bzero((char *)buf+PAGE_SIZE-resid,resid);
for(t=0; t<PAGE_SIZE-resid; t++) sum+=buf[t];
offset+=PAGE_SIZE;
}
}
printf("SUM=%d\n",sum);
if(buf) free(buf,M_TEMP);
imgp->proc->p_pad1[0]=0;
}
VOP_UNLOCK(imgp->vp);
if (error)
goto exec_fail_dealloc;
/*
* Copy out strings (args and env) and initialize stack base
*/
stack_base = exec_copyout_strings(imgp);
p->p_vmspace->vm_minsaddr = (char *)stack_base;
/*
* If custom stack fixup routine present for this process
* let it do the stack setup.
* Else stuff argument count as first item on stack
*/
if (p->p_sysent->sv_fixup)
(*p->p_sysent->sv_fixup)(&stack_base, imgp);
else
suword(--stack_base, imgp->argc);
/* close files on exec */
fdcloseexec(p);
/* reset caught signals */
execsigs(p);
/* name this process - nameiexec(p, ndp) */
len = min(ndp->ni_cnd.cn_namelen,MAXCOMLEN);
bcopy(ndp->ni_cnd.cn_nameptr, p->p_comm, len);
p->p_comm[len] = 0;
/*
* mark as execed, wakeup the process that vforked (if any) and tell
* it that it now has it's own resources back
*/
p->p_flag |= P_EXEC;
if (p->p_pptr && (p->p_flag & P_PPWAIT)) {
p->p_flag &= ~P_PPWAIT;
wakeup((caddr_t)p->p_pptr);
}
/*
* Implement image setuid/setgid. Disallow if the process is
* being traced.
*/
if ((attr.va_mode & (VSUID | VSGID)) &&
(p->p_flag & P_TRACED) == 0) {
/*
* Turn off syscall tracing for set-id programs, except for
* root.
*/
if (p->p_tracep && suser(p->p_ucred, &p->p_acflag)) {
p->p_traceflag = 0;
vrele(p->p_tracep);
p->p_tracep = NULL;
}
/*
* Set the new credentials.
*/
p->p_ucred = crcopy(p->p_ucred);
if (attr.va_mode & VSUID)
p->p_ucred->cr_uid = attr.va_uid;
if (attr.va_mode & VSGID)
p->p_ucred->cr_groups[0] = attr.va_gid;
p->p_flag |= P_SUGID;
} else {
if (p->p_ucred->cr_uid == p->p_cred->p_ruid &&
p->p_ucred->cr_gid == p->p_cred->p_rgid)
p->p_flag &= ~P_SUGID;
}
/*
* Implement correct POSIX saved-id behavior.
*/
p->p_cred->p_svuid = p->p_ucred->cr_uid;
p->p_cred->p_svgid = p->p_ucred->cr_gid;
/*
* Store the vp for use in procfs
*/
if (p->p_textvp) /* release old reference */
vrele(p->p_textvp);
VREF(ndp->ni_vp);
p->p_textvp = ndp->ni_vp;
/*
* If tracing the process, trap to debugger so breakpoints
* can be set before the program executes.
*/
if (p->p_flag & P_TRACED)
psignal(p, SIGTRAP);
/* clear "fork but no exec" flag, as we _are_ execing */
p->p_acflag &= ~AFORK;
/* Set entry address */
setregs(p, imgp->entry_addr, (u_long)stack_base);
/*
* free various allocated resources
*/
kmem_free_wakeup(exec_map, (vm_offset_t)imgp->stringbase, ARG_MAX);
if (bp != NULL)
brelse(bp);
else if (imgp->image_header != NULL)
free((void *)imgp->image_header, M_TEMP);
vrele(ndp->ni_vp);
FREE(ndp->ni_cnd.cn_pnbuf, M_NAMEI);
return (0);
exec_fail_dealloc:
if (imgp->stringbase != NULL)
kmem_free_wakeup(exec_map, (vm_offset_t)imgp->stringbase, ARG_MAX);
if (bp != NULL)
brelse(bp);
else if (imgp->image_header != NULL)
free((void *)imgp->image_header, M_TEMP);
if (ndp->ni_vp) {
vrele(ndp->ni_vp);
FREE(ndp->ni_cnd.cn_pnbuf, M_NAMEI);
}
exec_fail:
if (imgp->vmspace_destroyed) {
/* sorry, no more process anymore. exit gracefully */
exit1(p, W_EXITCODE(0, SIGABRT));
/* NOT REACHED */
return(0);
} else {
return(error);
}
}
/*
* Destroy old address space, and allocate a new stack
* The new stack is only SGROWSIZ large because it is grown
* automatically in trap.c.
*/
int
exec_new_vmspace(imgp)
struct image_params *imgp;
{
int error;
struct vmspace *vmspace = imgp->proc->p_vmspace;
caddr_t stack_addr = (caddr_t) (USRSTACK - SGROWSIZ);
imgp->vmspace_destroyed = 1;
/* Blow away entire process VM */
if (vmspace->vm_shm)
shmexit(imgp->proc);
pmap_remove_pages(&vmspace->vm_pmap, 0, USRSTACK);
vm_map_remove(&vmspace->vm_map, 0, USRSTACK);
/* Allocate a new stack */
error = vm_map_find(&vmspace->vm_map, NULL, 0, (vm_offset_t *)&stack_addr,
SGROWSIZ, FALSE, VM_PROT_ALL, VM_PROT_ALL, 0);
if (error)
return(error);
vmspace->vm_ssize = SGROWSIZ >> PAGE_SHIFT;
/* Initialize maximum stack address */
vmspace->vm_maxsaddr = (char *)USRSTACK - MAXSSIZ;
return(0);
}
/*
* Copy out argument and environment strings from the old process
* address space into the temporary string buffer.
*/
int
exec_extract_strings(imgp)
struct image_params *imgp;
{
char **argv, **envv;
char *argp, *envp;
int error, length;
/*
* extract arguments first
*/
argv = imgp->uap->argv;
if (argv) {
while ((argp = (caddr_t) fuword(argv++))) {
if (argp == (caddr_t) -1)
return (EFAULT);
if ((error = copyinstr(argp, imgp->stringp,
imgp->stringspace, &length))) {
if (error == ENAMETOOLONG)
return(E2BIG);
return (error);
}
imgp->stringspace -= length;
imgp->stringp += length;
imgp->argc++;
}
}
/*
* extract environment strings
*/
envv = imgp->uap->envv;
if (envv) {
while ((envp = (caddr_t) fuword(envv++))) {
if (envp == (caddr_t) -1)
return (EFAULT);
if ((error = copyinstr(envp, imgp->stringp,
imgp->stringspace, &length))) {
if (error == ENAMETOOLONG)
return(E2BIG);
return (error);
}
imgp->stringspace -= length;
imgp->stringp += length;
imgp->envc++;
}
}
return (0);
}
/*
* Copy strings out to the new process address space, constructing
* new arg and env vector tables. Return a pointer to the base
* so that it can be used as the initial stack pointer.
*/
int *
exec_copyout_strings(imgp)
struct image_params *imgp;
{
int argc, envc;
char **vectp;
char *stringp, *destp;
int *stack_base;
struct ps_strings *arginfo;
int szsigcode;
/*
* Calculate string base and vector table pointers.
* Also deal with signal trampoline code for this exec type.
*/
arginfo = PS_STRINGS;
szsigcode = *(imgp->proc->p_sysent->sv_szsigcode);
destp = (caddr_t)arginfo - szsigcode - SPARE_USRSPACE -
roundup((ARG_MAX - imgp->stringspace), sizeof(char *));
/*
* install sigcode
*/
if (szsigcode)
copyout(imgp->proc->p_sysent->sv_sigcode,
((caddr_t)arginfo - szsigcode), szsigcode);
/*
* If we have a valid auxargs ptr, prepare some room
* on the stack.
*/
if (imgp->auxargs)
/*
* The '+ 2' is for the null pointers at the end of each of the
* arg and env vector sets, and 'AT_COUNT*2' is room for the
* ELF Auxargs data.
*/
vectp = (char **)(destp - (imgp->argc + imgp->envc + 2 +
AT_COUNT*2) * sizeof(char*));
else
/*
* The '+ 2' is for the null pointers at the end of each of the
* arg and env vector sets
*/
vectp = (char **)
(destp - (imgp->argc + imgp->envc + 2) * sizeof(char*));
/*
* vectp also becomes our initial stack base
*/
stack_base = (int *)vectp;
stringp = imgp->stringbase;
argc = imgp->argc;
envc = imgp->envc;
/*
* Copy out strings - arguments and environment.
*/
copyout(stringp, destp, ARG_MAX - imgp->stringspace);
/*
* Fill in "ps_strings" struct for ps, w, etc.
*/
suword(&arginfo->ps_argvstr, (int)vectp);
suword(&arginfo->ps_nargvstr, argc);
/*
* Fill in argument portion of vector table.
*/
for (; argc > 0; --argc) {
suword(vectp++, (int)destp);
while (*stringp++ != 0)
destp++;
destp++;
}
/* a null vector table pointer seperates the argp's from the envp's */
suword(vectp++, 0);
suword(&arginfo->ps_envstr, (int)vectp);
suword(&arginfo->ps_nenvstr, envc);
/*
* Fill in environment portion of vector table.
*/
for (; envc > 0; --envc) {
suword(vectp++, (int)destp);
while (*stringp++ != 0)
destp++;
destp++;
}
/* end of vector table is a null pointer */
suword(vectp, 0);
return (stack_base);
}
/*
* Check permissions of file to execute.
* Return 0 for success or error code on failure.
*/
static int
exec_check_permissions(imgp)
struct image_params *imgp;
{
struct proc *p = imgp->proc;
struct vnode *vp = imgp->vp;
struct vattr *attr = imgp->attr;
int error;
/* Get file attributes */
error = VOP_GETATTR(vp, attr, p->p_ucred, p);
if (error)
return (error);
/*
* 1) Check if file execution is disabled for the filesystem that this
* file resides on.
* 2) Insure that at least one execute bit is on - otherwise root
* will always succeed, and we don't want to happen unless the
* file really is executable.
* 3) Insure that the file is a regular file.
*/
if ((vp->v_mount->mnt_flag & MNT_NOEXEC) ||
((attr->va_mode & 0111) == 0) ||
(attr->va_type != VREG)) {
return (EACCES);
}
/*
* Zero length files can't be exec'd
*/
if (attr->va_size == 0)
return (ENOEXEC);
/*
* Check for execute permission to file based on current credentials.
*/
error = VOP_ACCESS(vp, VEXEC, p->p_ucred, p);
if (error)
return (error);
/*
* Check number of open-for-writes on the file and deny execution
* if there are any.
*/
if (vp->v_writecount)
return (ETXTBSY);
/*
* Call filesystem specific open routine (which does nothing in the
* general case).
*/
error = VOP_OPEN(vp, FREAD, p->p_ucred, p);
if (error)
return (error);
/*
* Disable setuid/setgid if the filesystem prohibits it or if
* the process is being traced.
*/
if ((vp->v_mount->mnt_flag & MNT_NOSUID) || (p->p_flag & P_TRACED))
attr->va_mode &= ~(VSUID | VSGID);
return (0);
}
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