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libc/opendir: Improve behaviour of union uniquifier:

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* Reopen the directory using openat(fd, ".", ...) instead of opening the
  pathname again. This fixes a race condition where the meaning of the
  pathname changes and allows a reopen with fdopendir().
* Always reopen the directory for union stacks, not only when DTF_REWIND
  is passed. Applications should be able to fchdir(dirfd(dir)) and
  *at(dirfd(dir), ...). DTF_REWIND now does nothing.
This commit is contained in:
jilles 2013-02-24 20:53:32 +00:00
parent 60edaad227
commit b4ce52f66c
1 changed files with 26 additions and 25 deletions
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51
lib/libc/gen/opendir.c
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@ -49,7 +49,7 @@ __FBSDID("$FreeBSD$");
#include "gen-private.h"
#include "telldir.h"
static DIR * __opendir_common(int, const char *, int);
static DIR * __opendir_common(int, int);
/*
* Open a directory.
@ -78,7 +78,7 @@ fdopendir(int fd)
}
if (_fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
return (NULL);
return (__opendir_common(fd, NULL, DTF_HIDEW|DTF_NODUP));
return (__opendir_common(fd, DTF_HIDEW|DTF_NODUP));
}
DIR *
@ -92,7 +92,7 @@ __opendir2(const char *name, int flags)
O_RDONLY | O_NONBLOCK | O_DIRECTORY | O_CLOEXEC)) == -1)
return (NULL);
dir = __opendir_common(fd, name, flags);
dir = __opendir_common(fd, flags);
if (dir == NULL) {
saved_errno = errno;
_close(fd);
@ -113,7 +113,7 @@ opendir_compar(const void *p1, const void *p2)
* Common routine for opendir(3), __opendir2(3) and fdopendir(3).
*/
static DIR *
__opendir_common(int fd, const char *name, int flags)
__opendir_common(int fd, int flags)
{
DIR *dirp;
int incr;
@ -121,6 +121,8 @@ __opendir_common(int fd, const char *name, int flags)
int unionstack;
int fd2;
fd2 = -1;
if ((dirp = malloc(sizeof(DIR) + sizeof(struct _telldir))) == NULL)
return (NULL);
@ -165,7 +167,22 @@ __opendir_common(int fd, const char *name, int flags)
* entries into a buffer, sort the buffer, and
* remove duplicate entries by setting the inode
* number to zero.
*
* We reopen the directory because _getdirentries()
* on a MNT_UNION mount modifies the open directory,
* making it refer to the lower directory after the
* upper directory's entries are exhausted.
* This would otherwise break software that uses
* the directory descriptor for fchdir or *at
* functions, such as fts.c.
*/
if ((fd2 = _openat(fd, ".", O_RDONLY | O_CLOEXEC)) == -1) {
saved_errno = errno;
free(buf);
free(dirp);
errno = saved_errno;
return (NULL);
}
do {
/*
@ -181,7 +198,7 @@ __opendir_common(int fd, const char *name, int flags)
ddptr = buf + (len - space);
}
n = _getdirentries(fd, ddptr, space, &dirp->dd_seek);
n = _getdirentries(fd2, ddptr, space, &dirp->dd_seek);
if (n > 0) {
ddptr += n;
space -= n;
@ -191,25 +208,8 @@ __opendir_common(int fd, const char *name, int flags)
ddeptr = ddptr;
flags |= __DTF_READALL;
/*
* Re-open the directory.
* This has the effect of rewinding back to the
* top of the union stack and is needed by
* programs which plan to fchdir to a descriptor
* which has also been read -- see fts.c.
*/
if (flags & DTF_REWIND) {
if ((fd2 = _open(name, O_RDONLY | O_DIRECTORY |
O_CLOEXEC)) == -1) {
saved_errno = errno;
free(buf);
free(dirp);
errno = saved_errno;
return (NULL);
}
(void)_dup2(fd2, fd);
_close(fd2);
}
_close(fd2);
fd2 = -1;
/*
* There is now a buffer full of (possibly) duplicate
@ -293,7 +293,6 @@ __opendir_common(int fd, const char *name, int flags)
if (dirp->dd_buf == NULL)
goto fail;
dirp->dd_seek = 0;
flags &= ~DTF_REWIND;
}
dirp->dd_loc = 0;
@ -310,6 +309,8 @@ __opendir_common(int fd, const char *name, int flags)
fail:
saved_errno = errno;
if (fd2 != -1)
_close(fd2);
free(dirp);
errno = saved_errno;
return (NULL);