[PATCH]: non-readable binaries - binfmt_misc 2.6.0-test4

From: Zach, Yoav (yoav.zach_at_intel.com)
Date: 08/31/03

  • Next message: Adrian Bunk: "Re: create_proc_entry and !CONFIG_PROC_FS" 
    Date:	Mon, 1 Sep 2003 00:41:23 +0300
To: <akpm@osdl.org>, <torvalds@osdl.org>

    The proposed patch solves a problem for interpreters that need to
    execute a non-readable file, which cannot be read in userland. To handle
    such cases the interpreter must have the kernel load the binary on its
    behalf. The proposed patch handles this case by telling binfmt_misc, by
    a special flag in the registration string, to open the binary for
    reading and pass its descriptor as argv[1], instead of passing the
    binary's path. Old behavior of binfmt_misc is kept for interpreters
    which do not specify this special flag. The patch is against
    linux-2.6.0-test4. A similar one was posted twice on the list, on Aug.
    14 and 21, without significant response.

    ========================== start patch
    ==================================
    diff -r -U 3 linux-2.6.0-test4/fs/binfmt_misc.c linux/fs/binfmt_misc.c
    --- linux-2.6.0-test4/fs/binfmt_misc.c Sat Aug 23 02:54:23 2003
    +++ linux/fs/binfmt_misc.c Mon Sep 1 00:17:01 2003
    @@ -38,6 +38,8 @@
     
     enum {Enabled, Magic};
     #define MISC_FMT_PRESERVE_ARGV0 (1<<31)
    +#define MISC_FMT_OPEN_BINARY (1<<30)
    +
     
     typedef struct {
             struct list_head list;
    @@ -106,6 +108,10 @@
             char *iname_addr = iname;
             int retval;
     
    + int fd;
    + char fd_str[32];
    + char * fdsp = fd_str;
    +
             retval = -ENOEXEC;
             if (!enabled)
                     goto _ret;
    @@ -119,16 +125,41 @@
             if (!fmt)
                     goto _ret;
     
    - allow_write_access(bprm->file);
    - fput(bprm->file);
    - bprm->file = NULL;
    + if (fmt->flags & MISC_FMT_OPEN_BINARY) {
    + /* if the binary should be opened on behalf of the
    + * interpreter than keep it open and assign it a
    descriptor */
    + fd = get_unused_fd ();
    + if (fd < 0) {
    + allow_write_access(bprm->file);
    + fput(bprm->file);
    + bprm->file = NULL;
    + retval = fd;
    + goto _ret;
    + } else {
    + fd_install (fd, bprm->file);
    + sprintf (fd_str, "/dev/fd/%d", fd);
    + }
    + } else {
    + allow_write_access(bprm->file);
    + fput(bprm->file);
    + bprm->file = NULL;
    + }
    +
     
             /* Build args for interpreter */
             if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
                     remove_arg_zero(bprm);
             }
    - retval = copy_strings_kernel(1, &bprm->interp, bprm);
    +
    + if (fmt->flags & MISC_FMT_OPEN_BINARY) {
    + /* make argv[1] be the file descriptor */
    + retval = copy_strings_kernel(1, &fdsp, bprm);
    + } else {
    + /* make argv[1] be the path to the file */
    + retval = copy_strings_kernel(1, &bprm->interp, bprm);
    + }
             if (retval < 0) goto _ret;
    +
             bprm->argc++;
             retval = copy_strings_kernel(1, &iname_addr, bprm);
             if (retval < 0) goto _ret;
    @@ -139,9 +170,18 @@
             retval = PTR_ERR(file);
             if (IS_ERR(file))
                     goto _ret;
    - bprm->file = file;
     
    - retval = prepare_binprm(bprm);
    + /* get the file permissions and read its header */
    + if (fmt->flags & MISC_FMT_OPEN_BINARY) {
    + retval = prepare_binprm(bprm);
    + bprm->file = file;
    + memset(bprm->buf,0,BINPRM_BUF_SIZE);
    + retval =
    kernel_read(bprm->file,0,bprm->buf,BINPRM_BUF_SIZE);
    + } else {
    + bprm->file = file;
    + retval = prepare_binprm(bprm);
    + }
    +
             if (retval >= 0)
                     retval = search_binary_handler(bprm, regs);
     _ret:
    @@ -296,6 +336,10 @@
                     p++;
                     e->flags |= MISC_FMT_PRESERVE_ARGV0;
             }
    + if (*p == 'O') {
    + p++;
    + e->flags |= MISC_FMT_OPEN_BINARY;
    + }
     
             if (*p == '\n')
                     p++;
    ========================== end patch ==================================

    Yoav Zach
    Performance Tools Lab
    Intel Corp.

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