src/servers/vfs/exec.c

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/* This file handles the EXEC system call.  It performs the work as follows:
 *    - see if the permissions allow the file to be executed
 *    - read the header and extract the sizes
 *    - fetch the initial args and environment from the user space
 *    - allocate the memory for the new process
 *    - copy the initial stack from PM to the process
 *    - read in the text and data segments and copy to the process
 *    - take care of setuid and setgid bits
 *    - fix up 'mproc' table
 *    - tell kernel about EXEC
 *    - save offset to initial argc (for ps)
 *
 * The entry points into this file are:
 *   pm_exec:    perform the EXEC system call
 */

#include "fs.h"
#include <sys/stat.h>
#include <minix/callnr.h>
#include <minix/endpoint.h>
#include <minix/com.h>
#include <minix/u64.h>
#include <a.out.h>
#include <signal.h>
#include <string.h>
#include <dirent.h>
#include "fproc.h"
#include "param.h"
#include "vnode.h"
#include "vmnt.h"
#include <minix/vfsif.h>

FORWARD _PROTOTYPE( int exec_newmem, (int proc_e, vir_bytes text_bytes,
        vir_bytes data_bytes, vir_bytes bss_bytes, vir_bytes tot_bytes,
        vir_bytes frame_len, int sep_id,
        Dev_t st_dev, ino_t st_ino, time_t st_ctime, char *progname,
        int new_uid, int new_gid,
        vir_bytes *stack_topp, int *load_textp, int *allow_setuidp)     );
FORWARD _PROTOTYPE( int read_header, (struct vnode *vp, int *sep_id,
        vir_bytes *text_bytes, vir_bytes *data_bytes,
        vir_bytes *bss_bytes, phys_bytes *tot_bytes, vir_bytes *pc,
        int *hdrlenp)                                                   );
FORWARD _PROTOTYPE( int patch_stack, (struct vnode *vp,
        char stack[ARG_MAX], vir_bytes *stk_bytes)                      );
FORWARD _PROTOTYPE( int insert_arg, (char stack[ARG_MAX],
        vir_bytes *stk_bytes, char *arg, int replace)                   );
FORWARD _PROTOTYPE( void patch_ptr, (char stack[ARG_MAX],
                                                        vir_bytes base) );
FORWARD _PROTOTYPE( int read_seg, (struct vnode *vp, off_t off,
        int proc_e, int seg, phys_bytes seg_bytes)                      );
FORWARD _PROTOTYPE( void clo_exec, (struct fproc *rfp)                  );

#define ESCRIPT (-2000) /* Returned by read_header for a #! script. */
#define PTRSIZE sizeof(char *) /* Size of pointers in argv[] and envp[]. */

/*===========================================================================*
 *                              pm_exec                                      *
 *===========================================================================*/
PUBLIC int pm_exec(proc_e, path, path_len, frame, frame_len)
int proc_e;
char *path;
vir_bytes path_len;
char *frame;
vir_bytes frame_len;
{
/* Perform the execve(name, argv, envp) call.  The user library builds a
 * complete stack image, including pointers, args, environ, etc.  The stack
 * is copied to a buffer inside FS, and then to the new core image.
 */
  int r, r1, sep_id, round, proc_s, hdrlen, load_text, allow_setuid;
  vir_bytes text_bytes, data_bytes, bss_bytes, pc;
  phys_bytes tot_bytes;         /* total space for program, including gap */
  vir_bytes stack_top, vsp;
  off_t off;
  uid_t new_uid;
  gid_t new_gid;
  struct fproc *rfp;
  struct vnode *vp;
  time_t v_ctime;
  char *cp;
  struct stat sb;
  char progname[PROC_NAME_LEN];
  static char mbuf[ARG_MAX];    /* buffer for stack and zeroes */

  okendpt(proc_e, &proc_s);
  rfp = fp = &fproc[proc_s];
  who_e = proc_e;
  who_p = proc_s;
  super_user = (fp->fp_effuid == SU_UID ? TRUE : FALSE);   /* su? */

  /* Get the exec file name. */
  if ((r = fetch_name(path, path_len, 0)) != OK) return(r);

  /* Fetch the stack from the user before destroying the old core image. */
  if (frame_len > ARG_MAX) return(ENOMEM);      /* stack too big */
  r = sys_datacopy(proc_e, (vir_bytes) frame, SELF, (vir_bytes) mbuf,
                   (phys_bytes) frame_len);
  if (r != OK) { /* can't fetch stack (e.g. bad virtual addr) */
        printf("pm_exec: sys_datacopy failed\n");
        return(r);      
  }

  /* The default is to keep the original user and group IDs */
  new_uid = rfp->fp_effuid;
  new_gid = rfp->fp_effgid;

  for (round= 0; round < 2; round++) {
        /* round = 0 (first attempt), or 1 (interpreted script) */

        /* Save the name of the program */
        (cp= strrchr(user_fullpath, '/')) ? cp++ : (cp= user_fullpath);

        strncpy(progname, cp, PROC_NAME_LEN-1);
        progname[PROC_NAME_LEN-1] = '\0';

        /* Open executable */
        if ((vp = eat_path(PATH_NOFLAGS)) == NIL_VNODE) return(err_code);

        if ((vp->v_mode & I_TYPE) != I_REGULAR) 
                r = ENOEXEC;
        else if ((r1 = forbidden(vp, X_BIT)) != OK)
                r = r1;
        else
                r = req_stat(vp->v_fs_e, vp->v_inode_nr, FS_PROC_NR,
                             (char *) &sb, 0);
        if (r != OK) {
            put_vnode(vp);
            return(r);
        }

        v_ctime = sb.st_ctime;
        if (round == 0) {
            /* Deal with setuid/setgid executables */
            if (vp->v_mode & I_SET_UID_BIT) new_uid = vp->v_uid;
            if (vp->v_mode & I_SET_GID_BIT) new_gid = vp->v_gid;
        }

        /* Read the file header and extract the segment sizes. */
        r = read_header(vp, &sep_id, &text_bytes, &data_bytes, &bss_bytes, 
                        &tot_bytes, &pc, &hdrlen);
        if (r != ESCRIPT || round != 0)
                break;

        /* Get fresh copy of the file name. */
        if ((r = fetch_name(path, path_len, 0)) != OK) 
                printf("VFS pm_exec: 2nd fetch_name failed\n");
        else if ((r = patch_stack(vp, mbuf, &frame_len)) != OK) 
                printf("VFS pm_exec: patch_stack failed\n");
        put_vnode(vp);
        if (r != OK) return(r);
  }

  if (r != OK) {
        put_vnode(vp);
        return(ENOEXEC);
  }

  r = exec_newmem(proc_e, text_bytes, data_bytes, bss_bytes, tot_bytes,
                  frame_len, sep_id, vp->v_dev, vp->v_inode_nr, v_ctime, 
                  progname, new_uid, new_gid, &stack_top, &load_text,
                  &allow_setuid);
  if (r != OK) {
        printf("VFS: pm_exec: exec_newmem failed: %d\n", r);
        put_vnode(vp);
        return(r);
  }

  /* Patch up stack and copy it from FS to new core image. */
  vsp = stack_top;
  vsp -= frame_len;
  patch_ptr(mbuf, vsp);
  if ((r = sys_datacopy(SELF, (vir_bytes) mbuf, proc_e, (vir_bytes) vsp,
                   (phys_bytes)frame_len)) != OK) {
        printf("VFS: datacopy failed (%d) trying to copy to %p\n", r, vsp);
        return(r);
  }

  off = hdrlen;

  /* Read in text and data segments. */
  if (load_text) r = read_seg(vp, off, proc_e, T, text_bytes);
  off += text_bytes;
  if (r == OK) r = read_seg(vp, off, proc_e, D, data_bytes);
  put_vnode(vp);
  if (r != OK) return(r);
  clo_exec(rfp);

  if (allow_setuid) {
        rfp->fp_effuid = new_uid;
        rfp->fp_effgid = new_gid;
  }

  /* This child has now exec()ced. */
  rfp->fp_execced = 1;

  /* Check if this is a driver that can now be useful. */
  dmap_endpt_up(rfp->fp_endpoint);

  return(OK);
}


/*===========================================================================*
 *                              exec_newmem                                  *
 *===========================================================================*/
PRIVATE int exec_newmem(proc_e, text_bytes, data_bytes, bss_bytes, tot_bytes,
        frame_len, sep_id, st_dev, st_ino, st_ctime, progname,
        new_uid, new_gid, stack_topp, load_textp, allow_setuidp)
int proc_e;
vir_bytes text_bytes;
vir_bytes data_bytes;
vir_bytes bss_bytes;
vir_bytes tot_bytes;
vir_bytes frame_len;
int sep_id;
dev_t st_dev;
ino_t st_ino;
time_t st_ctime;
int new_uid;
int new_gid;
char *progname;
vir_bytes *stack_topp;
int *load_textp;
int *allow_setuidp;
{
  int r;
  struct exec_newmem e;
  message m;

  e.text_bytes = text_bytes;
  e.data_bytes = data_bytes;
  e.bss_bytes  = bss_bytes;
  e.tot_bytes  = tot_bytes;
  e.args_bytes = frame_len;
  e.sep_id     = sep_id;
  e.st_dev     = st_dev;
  e.st_ino     = st_ino;
  e.st_ctime   = st_ctime;
  e.new_uid    = new_uid;
  e.new_gid    = new_gid;
  strncpy(e.progname, progname, sizeof(e.progname)-1);
  e.progname[sizeof(e.progname)-1] = '\0';

  m.m_type = EXEC_NEWMEM;
  m.EXC_NM_PROC = proc_e;
  m.EXC_NM_PTR = (char *)&e;
  if ((r = sendrec(PM_PROC_NR, &m)) != OK) return(r);

  *stack_topp = m.m1_i1;
  *load_textp = !!(m.m1_i2 & EXC_NM_RF_LOAD_TEXT);
  *allow_setuidp = !!(m.m1_i2 & EXC_NM_RF_ALLOW_SETUID);

  return(m.m_type);
}


/*===========================================================================*
 *                              read_header                                  *
 *===========================================================================*/
PRIVATE int read_header(vp, sep_id, text_bytes, data_bytes, bss_bytes, 
                                                tot_bytes, pc, hdrlenp)
struct vnode *vp;               /* inode for reading exec file */
int *sep_id;                    /* true iff sep I&D */
vir_bytes *text_bytes;          /* place to return text size */
vir_bytes *data_bytes;          /* place to return initialized data size */
vir_bytes *bss_bytes;           /* place to return bss size */
phys_bytes *tot_bytes;          /* place to return total size */
vir_bytes *pc;                  /* program entry point (initial PC) */
int *hdrlenp;
{
/* Read the header and extract the text, data, bss and total sizes from it. */
  off_t pos;
  int r;
  u64_t new_pos;
  unsigned int cum_io;
  struct exec hdr;              /* a.out header is read in here */

  /* Read the header and check the magic number.  The standard MINIX header 
   * is defined in <a.out.h>.  It consists of 8 chars followed by 6 longs.
   * Then come 4 more longs that are not used here.
   *    Byte 0: magic number 0x01
   *    Byte 1: magic number 0x03
   *    Byte 2: normal = 0x10 (not checked, 0 is OK), separate I/D = 0x20
   *    Byte 3: CPU type, Intel 16 bit = 0x04, Intel 32 bit = 0x10, 
   *            Motorola = 0x0B, Sun SPARC = 0x17
   *    Byte 4: Header length = 0x20
   *    Bytes 5-7 are not used.
   *
   *    Now come the 6 longs
   *    Bytes  8-11: size of text segments in bytes
   *    Bytes 12-15: size of initialized data segment in bytes
   *    Bytes 16-19: size of bss in bytes
   *    Bytes 20-23: program entry point
   *    Bytes 24-27: total memory allocated to program (text, data + stack)
   *    Bytes 28-31: size of symbol table in bytes
   * The longs are represented in a machine dependent order,
   * little-endian on the 8088, big-endian on the 68000.
   * The header is followed directly by the text and data segments, and the 
   * symbol table (if any). The sizes are given in the header. Only the 
   * text and data segments are copied into memory by exec. The header is 
   * used here only. The symbol table is for the benefit of a debugger and 
   * is ignored here.
   */
  
  pos= 0;       /* Read from the start of the file */

  /* Issue request */
  r = req_readwrite(vp->v_fs_e, vp->v_inode_nr, cvul64(pos), READING,
                    FS_PROC_NR, (char*)&hdr, sizeof(hdr), &new_pos, &cum_io);
  if (r != OK) return r;

  /* Interpreted script? */
  if (((char*)&hdr)[0] == '#' && ((char*)&hdr)[1] == '!' && vp->v_size >= 2)
        return(ESCRIPT);

  if (vp->v_size < A_MINHDR) return(ENOEXEC);

  /* Check magic number, cpu type, and flags. */
  if (BADMAG(hdr)) return(ENOEXEC);
#if (CHIP == INTEL && _WORD_SIZE == 2)
  if (hdr.a_cpu != A_I8086) return(ENOEXEC);
#endif
#if (CHIP == INTEL && _WORD_SIZE == 4)
  if (hdr.a_cpu != A_I80386) return(ENOEXEC);
#endif
  if ((hdr.a_flags & ~(A_NSYM | A_EXEC | A_SEP)) != 0) return(ENOEXEC);

  *sep_id = !!(hdr.a_flags & A_SEP);        /* separate I & D or not */

  /* Get text and data sizes. */
  *text_bytes = (vir_bytes) hdr.a_text; /* text size in bytes */
  *data_bytes = (vir_bytes) hdr.a_data; /* data size in bytes */
  *bss_bytes  = (vir_bytes) hdr.a_bss;  /* bss size in bytes */
  *tot_bytes  = hdr.a_total;            /* total bytes to allocate for prog */
  if (*tot_bytes == 0) return(ENOEXEC);

  if (!*sep_id) {
        /* If I & D space is not separated, it is all considered data. Text=0*/
        *data_bytes += *text_bytes;
        *text_bytes = 0;
  }
  *pc = hdr.a_entry;    /* initial address to start execution */
  *hdrlenp = hdr.a_hdrlen & BYTE;               /* header length */

  return(OK);
}


/*===========================================================================*
 *                              patch_stack                                  *
 *===========================================================================*/
PRIVATE int patch_stack(vp, stack, stk_bytes)
struct vnode *vp;               /* pointer for open script file */
char stack[ARG_MAX];            /* pointer to stack image within FS */
vir_bytes *stk_bytes;           /* size of initial stack */
{
/* Patch the argument vector to include the path name of the script to be
 * interpreted, and all strings on the #! line.  Returns the path name of
 * the interpreter.
 */
  enum { INSERT=FALSE, REPLACE=TRUE };
  int n, r;
  off_t pos;
  char *sp, *interp = NULL;
  u64_t new_pos;
  unsigned int cum_io;
  char buf[_MAX_BLOCK_SIZE];

  /* Make user_fullpath the new argv[0]. */
  if (!insert_arg(stack, stk_bytes, user_fullpath, REPLACE)) return(ENOMEM);

  pos = 0;      /* Read from the start of the file */

  /* Issue request */
  r = req_readwrite(vp->v_fs_e, vp->v_inode_nr, cvul64(pos), READING,
                    FS_PROC_NR, buf, _MAX_BLOCK_SIZE, &new_pos, &cum_io);
  if (r != OK) return(r);
  
  n = vp->v_size;
  if (n > _MAX_BLOCK_SIZE)
        n = _MAX_BLOCK_SIZE;
  if (n < 2) return ENOEXEC;
  
  sp = &(buf[2]);                               /* just behind the #! */
  n -= 2;
  if (n > PATH_MAX) n = PATH_MAX;

  /* Use the user_fullpath variable for temporary storage */
  memcpy(user_fullpath, sp, n);

  if ((sp = memchr(user_fullpath, '\n', n)) == NULL) /* must be a proper line */
        return(ENOEXEC);

  /* Move sp backwards through script[], prepending each string to stack. */
  for (;;) {
        /* skip spaces behind argument. */
        while (sp > user_fullpath && (*--sp == ' ' || *sp == '\t')) {}
        if (sp == user_fullpath) break;

        sp[1] = 0;
        /* Move to the start of the argument. */
        while (sp > user_fullpath && sp[-1] != ' ' && sp[-1] != '\t') --sp;

        interp = sp;
        if (!insert_arg(stack, stk_bytes, sp, INSERT)) return(ENOMEM);
  }

  /* Round *stk_bytes up to the size of a pointer for alignment contraints. */
  *stk_bytes= ((*stk_bytes + PTRSIZE - 1) / PTRSIZE) * PTRSIZE;

  if (interp != user_fullpath)
        memmove(user_fullpath, interp, strlen(interp)+1);
  return(OK);
}

/*===========================================================================*
 *                              insert_arg                                   *
 *===========================================================================*/
PRIVATE int insert_arg(stack, stk_bytes, arg, replace)
char stack[ARG_MAX];            /* pointer to stack image within PM */
vir_bytes *stk_bytes;           /* size of initial stack */
char *arg;                      /* argument to prepend/replace as new argv[0] */
int replace;
{
/* Patch the stack so that arg will become argv[0].  Be careful, the stack may
 * be filled with garbage, although it normally looks like this:
 *      nargs argv[0] ... argv[nargs-1] NULL envp[0] ... NULL
 * followed by the strings "pointed" to by the argv[i] and the envp[i].  The
 * pointers are really offsets from the start of stack.
 * Return true iff the operation succeeded.
 */
  int offset, a0, a1, old_bytes = *stk_bytes;

  /* Prepending arg adds at least one string and a zero byte. */
  offset = strlen(arg) + 1;

  a0 = (int) ((char **) stack)[1];      /* argv[0] */
  if (a0 < 4 * PTRSIZE || a0 >= old_bytes) return(FALSE);

  a1 = a0;                      /* a1 will point to the strings to be moved */
  if (replace) {
        /* Move a1 to the end of argv[0][] (argv[1] if nargs > 1). */
        do {
                if (a1 == old_bytes) return(FALSE);
                --offset;
        } while (stack[a1++] != 0);
  } else {
        offset += PTRSIZE;      /* new argv[0] needs new pointer in argv[] */
        a0 += PTRSIZE;          /* location of new argv[0][]. */
  }

  /* stack will grow by offset bytes (or shrink by -offset bytes) */
  if ((*stk_bytes += offset) > ARG_MAX) return(FALSE);

  /* Reposition the strings by offset bytes */
  memmove(stack + a1 + offset, stack + a1, old_bytes - a1);

  strcpy(stack + a0, arg);      /* Put arg in the new space. */

  if (!replace) {
        /* Make space for a new argv[0]. */
        memmove(stack + 2 * PTRSIZE, stack + 1 * PTRSIZE, a0 - 2 * PTRSIZE);

        ((char **) stack)[0]++; /* nargs++; */
  }
  /* Now patch up argv[] and envp[] by offset. */
  patch_ptr(stack, (vir_bytes) offset);
  ((char **) stack)[1] = (char *) a0;   /* set argv[0] correctly */
  return(TRUE);
}


/*===========================================================================*
 *                              patch_ptr                                    *
 *===========================================================================*/
PRIVATE void patch_ptr(stack, base)
char stack[ARG_MAX];            /* pointer to stack image within PM */
vir_bytes base;                 /* virtual address of stack base inside user */
{
/* When doing an exec(name, argv, envp) call, the user builds up a stack
 * image with arg and env pointers relative to the start of the stack.  Now
 * these pointers must be relocated, since the stack is not positioned at
 * address 0 in the user's address space.
 */

  char **ap, flag;
  vir_bytes v;

  flag = 0;                     /* counts number of 0-pointers seen */
  ap = (char **) stack;         /* points initially to 'nargs' */
  ap++;                         /* now points to argv[0] */
  while (flag < 2) {
        if (ap >= (char **) &stack[ARG_MAX]) return;    /* too bad */
        if (*ap != NULL) {
                v = (vir_bytes) *ap;    /* v is relative pointer */
                v += base;              /* relocate it */
                *ap = (char *) v;       /* put it back */
        } else {
                flag++;
        }
        ap++;
  }
}


/*===========================================================================*
 *                              read_seg                                     *
 *===========================================================================*/
PRIVATE int read_seg(vp, off, proc_e, seg, seg_bytes)
struct vnode *vp;               /* inode descriptor to read from */
off_t off;                      /* offset in file */
int proc_e;                     /* process number (endpoint) */
int seg;                        /* T, D, or S */
phys_bytes seg_bytes;           /* how much is to be transferred? */
{
/*
 * The byte count on read is usually smaller than the segment count, because
 * a segment is padded out to a click multiple, and the data segment is only
 * partially initialized.
 */
  int r;
  unsigned n, o;
  u64_t new_pos;
  unsigned int cum_io;
  char buf[1024];

  /* Make sure that the file is big enough */
  if (vp->v_size < off+seg_bytes) return(EIO);

  if (seg != D) {
        /* We have to use a copy loop until safecopies support segments */
        o = 0;
        while (o < seg_bytes) {
                n = seg_bytes - o;
                if (n > sizeof(buf))
                        n = sizeof(buf);

                if ((r = req_readwrite(vp->v_fs_e,vp->v_inode_nr,cvul64(off+o), READING, FS_PROC_NR, buf,
                                       n, &new_pos, &cum_io)) != OK) {
                        printf("VFS: read_seg: req_readwrite failed (text)\n");
                        return(r);
                }

                if (cum_io != n) {
                        printf(
                "VFSread_seg segment has not been read properly by exec() \n");
                        return(EIO);
                }

                if ((r = sys_vircopy(FS_PROC_NR, D, (vir_bytes)buf, proc_e,
                                     seg, o, n)) != OK) {
                        printf("VFS: read_seg: copy failed (text)\n");
                        return(r);
                }

                o += n;
        }
        return(OK);
  }
  
  if ((r = req_readwrite(vp->v_fs_e, vp->v_inode_nr, cvul64(off), READING,
                         proc_e, 0, seg_bytes, &new_pos, &cum_io)) != OK) {
        printf("VFS: read_seg: req_readwrite failed (data)\n");
        return(r);
  }
  
  if (r == OK && cum_io != seg_bytes)
        printf("VFSread_seg segment has not been read properly by exec()\n");

  return(r); 
}


/*===========================================================================*
 *                              clo_exec                                     *
 *===========================================================================*/
PRIVATE void clo_exec(rfp)
struct fproc *rfp;
{
/* Files can be marked with the FD_CLOEXEC bit (in fp->fp_cloexec).  
 */
  int i;

  /* Check the file desriptors one by one for presence of FD_CLOEXEC. */
  for (i = 0; i < OPEN_MAX; i++)
        if ( FD_ISSET(i, &rfp->fp_cloexec_set))
                (void) close_fd(rfp, i);
}

---