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shred: avoid rename race

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Use renameat2 to avoid a rename race condition, on recent-enough
GNU/Linux.
* bootstrap.conf (gnulib_modules): Add renameat2.
* src/shred.c: Include renameat2.h.
(wipename): Use renameat2 instead of rename.
This commit is contained in:
Paul Eggert
2017-07-30 17:11:24 -07:00
parent ac6956bbce
commit 2ae1460dad
2 changed files with 32 additions and 44 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
bootstrap.conf
View File

@@ -206,6 +206,7 @@ gnulib_modules="
remove
rename
renameat
renameat2
rmdir
root-dev-ino
rpmatch

75
src/shred.c
View File

@@ -93,6 +93,7 @@
#include "human.h"
#include "randint.h"
#include "randread.h"
#include "renameat2.h"
#include "stat-size.h"
/* Default number of times to overwrite. */
@@ -1077,7 +1078,6 @@ wipename (char *oldname, char const *qoldname, struct Options const *flags)
{
char *newname = xstrdup (oldname);
char *base = last_component (newname);
size_t len = base_len (base);
char *dir = dir_name (newname);
char *qdir = xstrdup (quotef (dir));
bool first = true;
@@ -1090,49 +1090,36 @@ wipename (char *oldname, char const *qoldname, struct Options const *flags)
if (flags->verbose)
error (0, 0, _("%s: removing"), qoldname);
while ((flags->remove_file != remove_unlink) && len)
{
memset (base, nameset[0], len);
base[len] = 0;
do
{
struct stat st;
if (lstat (newname, &st) < 0)
{
if (rename (oldname, newname) == 0)
{
if (0 <= dir_fd && dosync (dir_fd, qdir) != 0)
ok = false;
if (flags->verbose)
{
/*
* People seem to understand this better than talking
* about renaming oldname. newname doesn't need
* quoting because we picked it. oldname needs to
* be quoted only the first time.
*/
char const *old = (first ? qoldname : oldname);
error (0, 0, _("%s: renamed to %s"),
old, newname);
first = false;
}
memcpy (oldname + (base - newname), base, len + 1);
break;
}
else
{
/* The rename failed: give up on this length. */
break;
}
}
else
{
/* newname exists, so increment BASE so we use another */
}
}
while (incname (base, len));
len--;
}
if (flags->remove_file != remove_unlink)
for (size_t len = base_len (base); len != 0; len--)
{
memset (base, nameset[0], len);
base[len] = 0;
bool rename_ok;
while (! (rename_ok = (renameat2 (AT_FDCWD, oldname, AT_FDCWD, newname,
RENAME_NOREPLACE)
== 0))
&& errno == EEXIST && incname (base, len))
continue;
if (rename_ok)
{
if (0 <= dir_fd && dosync (dir_fd, qdir) != 0)
ok = false;
if (flags->verbose)
{
/* People seem to understand this better than talking
about renaming OLDNAME. NEWNAME doesn't need
quoting because we picked it. OLDNAME needs to be
quoted only the first time. */
char const *old = first ? qoldname : oldname;
error (0, 0, _("%s: renamed to %s"), old, newname);
first = false;
}
memcpy (oldname + (base - newname), base, len + 1);
break;
}
}
if (unlink (oldname) != 0)
{
error (0, errno, _("%s: failed to remove"), qoldname);