Author: jilles
Date: Sun Feb 24 20:53:32 2013
New Revision: 247236
URL: http://svnweb.freebsd.org/changeset/base/247236
Log:
libc/opendir: Improve behaviour of union uniquifier:
* 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.
Modified:
head/lib/libc/gen/opendir.c
Modified: head/lib/libc/gen/opendir.c
==============================================================================
--- head/lib/libc/gen/opendir.c Sun Feb 24 19:49:02 2013 (r247235)
+++ head/lib/libc/gen/opendir.c Sun Feb 24 20:53:32 2013 (r247236)
@@ -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 voi
* 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 *nam
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 *nam
* 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 *nam
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 *nam
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 *nam
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 *nam
fail:
saved_errno = errno;
+ if (fd2 != -1)
+ _close(fd2);
free(dirp);
errno = saved_errno;
return (NULL);
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