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(defined_S_IFMT): New macro.

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Include stat-macros.h.
Include stdlib.h, for abort().
Don't include stdio.h or assert.h; no longer needed.
(same_file_type): Don't assume S_IFMT is defined, as POSIX
does not require this.  Don't assume S_IFCHR and S_IFBLK have
their usual sort of bit pattern.
(fchmod_new): Open with O_NOCTTY for as well, for minor
improvement on hosts where that matters.  Don't bother to assert,
since the caller (in this source file) checks the same thing.
Discard any errno from a close failure, for consistency with other
code.
This commit is contained in:
Paul Eggert 2005-12-27 07:55:50 +00:00
parent cc4d59e9cd
commit 0d7468cabd
1 changed files with 43 additions and 34 deletions
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77
lib/chmod-safer.c
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@ -23,16 +23,21 @@
#include "chmod-safer.h"
#ifdef S_IFMT
# define defined_S_IFMT true
#else
# define defined_S_IFMT false
#endif
#include "stat-macros.h"
#include <stdbool.h>
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include "fcntl--.h" /* for the open->open_safer mapping */
#if !defined O_NOFOLLOW
#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif
@ -48,12 +53,17 @@ static inline bool
same_file_type (struct stat const *st, dev_t device, mode_t type)
{
/* The types must always match. */
if ( ! (st->st_mode & type))
if (! (defined_S_IFMT ? (st->st_mode & S_IFMT) == type
: type == S_IFDIR ? S_ISDIR (st->st_mode)
: type == S_IFIFO ? S_ISFIFO (st->st_mode)
: type == S_IFBLK ? S_ISBLK (st->st_mode)
: type == S_IFCHR ? S_ISCHR (st->st_mode)
: (abort (), false)))
return false;
/* For character and block devices, the major and minor device
numbers must match, too. */
if (type & (S_IFCHR | S_IFBLK))
if (S_ISBLK (type) || S_ISCHR (type))
return st->st_rdev == device;
return true;
@ -66,40 +76,39 @@ same_file_type (struct stat const *st, dev_t device, mode_t type)
static int
fchmod_new (char const *file, mode_t mode, dev_t device, mode_t file_type)
{
int fail = 1;
int result = 0;
struct stat sb;
int saved_errno = 0;
int fd = open (file, O_NOFOLLOW | O_RDONLY | O_NDELAY);
int fd = open (file, O_RDONLY | O_NOCTTY | O_NOFOLLOW | O_NONBLOCK);
int saved_errno;
assert (O_NOFOLLOW);
if (fd < 0)
return -1;
if (0 <= fd
&& fstat (fd, &sb) == 0
/* Given the entry we've just created, if its link count is
not 1 or its type/device has changed, then someone may be
trying to do something nasty. However, the risk of such an
attack is so low that it isn't worth a special diagnostic.
Simply skip the fchmod and set errno, so that the
code below reports the failure to set permissions.
Note that we don't check the link count if the expected
type is `directory'. */
&& (((sb.st_nlink == 1 || file_type == S_IFDIR)
&& same_file_type (&sb, device, file_type))
|| ((errno = EACCES), 0))
&& fchmod (fd, mode) == 0)
/* Given the entry we've just created, if its link count is
not 1 or its type/device has changed, then someone may be
trying to do something nasty. However, the risk of such an
attack is so low that it isn't worth a special diagnostic.
Simply skip the fchmod and set errno, so that the
code below reports the failure to set permissions.
Note that we don't check the link count if the expected
type is `directory'. */
result = fstat (fd, &sb);
if (result == 0)
{
fail = 0;
}
else
{
saved_errno = errno;
if ((sb.st_nlink == 1 || S_ISDIR (file_type))
&& same_file_type (&sb, device, file_type))
result = fchmod (fd, mode);
else
{
errno = EACCES;
result = -1;
}
}
if (0 <= fd && close (fd) != 0 && saved_errno == 0)
saved_errno = errno;
saved_errno = errno;
close (fd);
errno = saved_errno;
return fail;
return result;
}
/* Use a safer variant of chmod, if the underlying system facilities permit.