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[PATCH] uml: make execvp safe for our usage 

Reimplement execvp for our purposes - after we call fork() it is fundamentally
unsafe to use the kernel allocator - current is not valid there.  So we simply
pass to our modified execvp() a preallocated buffer.  This fixes a real bug
and works very well in testing (I've seen indirectly warning messages from the
forked thread - they went on the pipe connected to its stdout and where read
as a number by UML, when calling read_output().  I verified the obtained
number corresponded to "BUG:").

The added use of __cant_sleep() is not a new bug since __cant_sleep() is
already used in the same function - passing an atomicity parameter would be
better but it would require huge change, stating that this function must not
be called in atomic context and can sleep is a better idea (will make sure of
this gradually).

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Paolo 'Blaisorblade' Giarrusso 2006-11-25 11:09:39 -08:00 committed by Linus Torvalds
parent 9dce447a54
commit 5d48545e5e
4 changed files with 166 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/um/include/os.h
View File

@ -233,6 +233,8 @@ extern unsigned long __do_user_copy(void *to, const void *from, int n,
void (*op)(void *to, const void *from,
int n), int *faulted_out);
/* execvp.c */
extern int execvp_noalloc(char *buf, const char *file, char *const argv[]);
/* helper.c */
extern int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
unsigned long *stack_out);

10
arch/um/os-Linux/Makefile
View File

@ -3,8 +3,8 @@
# Licensed under the GPL
#
obj-y = aio.o elf_aux.o file.o helper.o irq.o main.o mem.o process.o sigio.o \
signal.o start_up.o time.o trap.o tty.o uaccess.o umid.o tls.o \
obj-y = aio.o elf_aux.o execvp.o file.o helper.o irq.o main.o mem.o process.o \
sigio.o signal.o start_up.o time.o trap.o tty.o uaccess.o umid.o tls.o \
user_syms.o util.o drivers/ sys-$(SUBARCH)/
obj-$(CONFIG_MODE_SKAS) += skas/
@ -15,9 +15,9 @@ user-objs-$(CONFIG_MODE_TT) += tt.o
obj-$(CONFIG_TTY_LOG) += tty_log.o
user-objs-$(CONFIG_TTY_LOG) += tty_log.o
USER_OBJS := $(user-objs-y) aio.o elf_aux.o file.o helper.o irq.o main.o mem.o \
process.o sigio.o signal.o start_up.o time.o trap.o tty.o tls.o \
uaccess.o umid.o util.o
USER_OBJS := $(user-objs-y) aio.o elf_aux.o execvp.o file.o helper.o irq.o \
main.o mem.o process.o sigio.o signal.o start_up.o time.o trap.o tty.o \
tls.o uaccess.o umid.o util.o
CFLAGS_user_syms.o += -DSUBARCH_$(SUBARCH)

149
arch/um/os-Linux/execvp.c Normal file
View File

@ -0,0 +1,149 @@
/* Copyright (C) 2006 by Paolo Giarrusso - modified from glibc' execvp.c.
Original copyright notice follows:
Copyright (C) 1991,92,1995-99,2002,2004 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <unistd.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <limits.h>
#ifndef TEST
#include "um_malloc.h"
#else
#include <stdio.h>
#define um_kmalloc malloc
#endif
#include "os.h"
/* Execute FILE, searching in the `PATH' environment variable if it contains
no slashes, with arguments ARGV and environment from `environ'. */
int execvp_noalloc(char *buf, const char *file, char *const argv[])
{
if (*file == '\0') {
return -ENOENT;
}
if (strchr (file, '/') != NULL) {
/* Don't search when it contains a slash. */
execv(file, argv);
} else {
int got_eacces;
size_t len, pathlen;
char *name, *p;
char *path = getenv("PATH");
if (path == NULL)
path = ":/bin:/usr/bin";
len = strlen(file) + 1;
pathlen = strlen(path);
/* Copy the file name at the top. */
name = memcpy(buf + pathlen + 1, file, len);
/* And add the slash. */
*--name = '/';
got_eacces = 0;
p = path;
do {
char *startp;
path = p;
//Let's avoid this GNU extension.
//p = strchrnul (path, ':');
p = strchr(path, ':');
if (!p)
p = strchr(path, '\0');
if (p == path)
/* Two adjacent colons, or a colon at the beginning or the end
of `PATH' means to search the current directory. */
startp = name + 1;
else
startp = memcpy(name - (p - path), path, p - path);
/* Try to execute this name. If it works, execv will not return. */
execv(startp, argv);
/*
if (errno == ENOEXEC) {
}
*/
switch (errno) {
case EACCES:
/* Record the we got a `Permission denied' error. If we end
up finding no executable we can use, we want to diagnose
that we did find one but were denied access. */
got_eacces = 1;
case ENOENT:
case ESTALE:
case ENOTDIR:
/* Those errors indicate the file is missing or not executable
by us, in which case we want to just try the next path
directory. */
case ENODEV:
case ETIMEDOUT:
/* Some strange filesystems like AFS return even
stranger error numbers. They cannot reasonably mean
anything else so ignore those, too. */
case ENOEXEC:
/* We won't go searching for the shell
* if it is not executable - the Linux
* kernel already handles this enough,
* for us. */
break;
default:
/* Some other error means we found an executable file, but
something went wrong executing it; return the error to our
caller. */
return -errno;
}
} while (*p++ != '\0');
/* We tried every element and none of them worked. */
if (got_eacces)
/* At least one failure was due to permissions, so report that
error. */
return -EACCES;
}
/* Return the error from the last attempt (probably ENOENT). */
return -errno;
}
#ifdef TEST
int main(int argc, char**argv)
{
char buf[PATH_MAX];
int ret;
argc--;
if (!argc) {
fprintf(stderr, "Not enough arguments\n");
return 1;
}
argv++;
if (ret = execvp_noalloc(buf, argv[0], argv)) {
errno = -ret;
perror("execvp_noalloc");
}
return 0;
}
#endif

14
arch/um/os-Linux/helper.c
View File

@ -8,18 +8,21 @@
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <limits.h>
#include <sys/signal.h>
#include <sys/wait.h>
#include "user.h"
#include "kern_util.h"
#include "user_util.h"
#include "os.h"
#include "um_malloc.h"
struct helper_data {
void (*pre_exec)(void*);
void *pre_data;
char **argv;
int fd;
char *buf;
};
/* Debugging aid, changed only from gdb */
@ -41,9 +44,8 @@ static int helper_child(void *arg)
}
if (data->pre_exec != NULL)
(*data->pre_exec)(data->pre_data);
execvp(argv[0], argv);
errval = -errno;
printk("helper_child - execve of '%s' failed - errno = %d\n", argv[0], errno);
errval = execvp_noalloc(data->buf, argv[0], argv);
printk("helper_child - execvp of '%s' failed - errno = %d\n", argv[0], -errval);
os_write_file(data->fd, &errval, sizeof(errval));
kill(os_getpid(), SIGKILL);
return 0;
@ -84,11 +86,13 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
data.pre_data = pre_data;
data.argv = argv;
data.fd = fds[1];
data.buf = __cant_sleep() ? um_kmalloc_atomic(PATH_MAX) :
um_kmalloc(PATH_MAX);
pid = clone(helper_child, (void *) sp, CLONE_VM | SIGCHLD, &data);
if (pid < 0) {
ret = -errno;
printk("run_helper : clone failed, errno = %d\n", errno);
goto out_close;
goto out_free2;
}
close(fds[1]);
@ -109,6 +113,8 @@ int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv,
CATCH_EINTR(waitpid(pid, NULL, 0));
}
out_free2:
kfree(data.buf);
out_close:
if (fds[1] != -1)
close(fds[1]);