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git/tempfile.c
Ben Wijen 05d1ed6148 mingw: ensure temporary file handles are not inherited by child processes
When the index is locked and child processes inherit the handle to
said lock and the parent process wants to remove the lock before the
child process exits, on Windows there is a problem: it won't work
because files cannot be deleted if a process holds a handle on them.
The symptom:

    Rename from 'xxx/.git/index.lock' to 'xxx/.git/index' failed.
    Should I try again? (y/n)

Spawning child processes with bInheritHandles==FALSE would not work
because no file handles would be inherited, not even the hStdXxx
handles in STARTUPINFO (stdin/stdout/stderr).

Opening every file with O_NOINHERIT does not work, either, as e.g.
git-upload-pack expects inherited file handles.

This leaves us with the only way out: creating temp files with the
O_NOINHERIT flag. This flag is Windows-specific, however. For our
purposes, it is equivalent to O_CLOEXEC (which does not exist on
Windows), so let's just open temporary files with the O_CLOEXEC flag and
map that flag to O_NOINHERIT on Windows.

As Eric Wong pointed out, we need to be careful to handle the case where
the Linux headers used to compile Git support O_CLOEXEC but the Linux
kernel used to run Git does not: it returns an EINVAL.

This fixes the test that we just introduced to demonstrate the problem.

Signed-off-by: Ben Wijen <ben@wijen.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-23 09:09:55 -07:00

310 lines
8.2 KiB
C

/*
* State diagram and cleanup
* -------------------------
*
* If the program exits while a temporary file is active, we want to
* make sure that we remove it. This is done by remembering the active
* temporary files in a linked list, `tempfile_list`. An `atexit(3)`
* handler and a signal handler are registered, to clean up any active
* temporary files.
*
* Because the signal handler can run at any time, `tempfile_list` and
* the `tempfile` objects that comprise it must be kept in
* self-consistent states at all times.
*
* The possible states of a `tempfile` object are as follows:
*
* - Uninitialized. In this state the object's `on_list` field must be
* zero but the rest of its contents need not be initialized. As
* soon as the object is used in any way, it is irrevocably
* registered in `tempfile_list`, and `on_list` is set.
*
* - Active, file open (after `create_tempfile()` or
* `reopen_tempfile()`). In this state:
*
* - the temporary file exists
* - `active` is set
* - `filename` holds the filename of the temporary file
* - `fd` holds a file descriptor open for writing to it
* - `fp` holds a pointer to an open `FILE` object if and only if
* `fdopen_tempfile()` has been called on the object
* - `owner` holds the PID of the process that created the file
*
* - Active, file closed (after successful `close_tempfile()`). Same
* as the previous state, except that the temporary file is closed,
* `fd` is -1, and `fp` is `NULL`.
*
* - Inactive (after `delete_tempfile()`, `rename_tempfile()`, a
* failed attempt to create a temporary file, or a failed
* `close_tempfile()`). In this state:
*
* - `active` is unset
* - `filename` is empty (usually, though there are transitory
* states in which this condition doesn't hold). Client code should
* *not* rely on the filename being empty in this state.
* - `fd` is -1 and `fp` is `NULL`
* - the object is left registered in the `tempfile_list`, and
* `on_list` is set.
*
* A temporary file is owned by the process that created it. The
* `tempfile` has an `owner` field that records the owner's PID. This
* field is used to prevent a forked process from deleting a temporary
* file created by its parent.
*/
#include "cache.h"
#include "tempfile.h"
#include "sigchain.h"
static struct tempfile *volatile tempfile_list;
static void remove_tempfiles(int skip_fclose)
{
pid_t me = getpid();
while (tempfile_list) {
if (tempfile_list->owner == me) {
/* fclose() is not safe to call in a signal handler */
if (skip_fclose)
tempfile_list->fp = NULL;
delete_tempfile(tempfile_list);
}
tempfile_list = tempfile_list->next;
}
}
static void remove_tempfiles_on_exit(void)
{
remove_tempfiles(0);
}
static void remove_tempfiles_on_signal(int signo)
{
remove_tempfiles(1);
sigchain_pop(signo);
raise(signo);
}
/*
* Initialize *tempfile if necessary and add it to tempfile_list.
*/
static void prepare_tempfile_object(struct tempfile *tempfile)
{
if (!tempfile_list) {
/* One-time initialization */
sigchain_push_common(remove_tempfiles_on_signal);
atexit(remove_tempfiles_on_exit);
}
if (tempfile->active)
die("BUG: prepare_tempfile_object called for active object");
if (!tempfile->on_list) {
/* Initialize *tempfile and add it to tempfile_list: */
tempfile->fd = -1;
tempfile->fp = NULL;
tempfile->active = 0;
tempfile->owner = 0;
strbuf_init(&tempfile->filename, 0);
tempfile->next = tempfile_list;
tempfile_list = tempfile;
tempfile->on_list = 1;
} else if (tempfile->filename.len) {
/* This shouldn't happen, but better safe than sorry. */
die("BUG: prepare_tempfile_object called for improperly-reset object");
}
}
/* Make sure errno contains a meaningful value on error */
int create_tempfile(struct tempfile *tempfile, const char *path)
{
prepare_tempfile_object(tempfile);
strbuf_add_absolute_path(&tempfile->filename, path);
tempfile->fd = open(tempfile->filename.buf,
O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
/* Try again w/o O_CLOEXEC: the kernel might not support it */
tempfile->fd = open(tempfile->filename.buf,
O_RDWR | O_CREAT | O_EXCL, 0666);
if (tempfile->fd < 0) {
strbuf_reset(&tempfile->filename);
return -1;
}
tempfile->owner = getpid();
tempfile->active = 1;
if (adjust_shared_perm(tempfile->filename.buf)) {
int save_errno = errno;
error("cannot fix permission bits on %s", tempfile->filename.buf);
delete_tempfile(tempfile);
errno = save_errno;
return -1;
}
return tempfile->fd;
}
void register_tempfile(struct tempfile *tempfile, const char *path)
{
prepare_tempfile_object(tempfile);
strbuf_add_absolute_path(&tempfile->filename, path);
tempfile->owner = getpid();
tempfile->active = 1;
}
int mks_tempfile_sm(struct tempfile *tempfile,
const char *template, int suffixlen, int mode)
{
prepare_tempfile_object(tempfile);
strbuf_add_absolute_path(&tempfile->filename, template);
tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
if (tempfile->fd < 0) {
strbuf_reset(&tempfile->filename);
return -1;
}
tempfile->owner = getpid();
tempfile->active = 1;
return tempfile->fd;
}
int mks_tempfile_tsm(struct tempfile *tempfile,
const char *template, int suffixlen, int mode)
{
const char *tmpdir;
prepare_tempfile_object(tempfile);
tmpdir = getenv("TMPDIR");
if (!tmpdir)
tmpdir = "/tmp";
strbuf_addf(&tempfile->filename, "%s/%s", tmpdir, template);
tempfile->fd = git_mkstemps_mode(tempfile->filename.buf, suffixlen, mode);
if (tempfile->fd < 0) {
strbuf_reset(&tempfile->filename);
return -1;
}
tempfile->owner = getpid();
tempfile->active = 1;
return tempfile->fd;
}
int xmks_tempfile_m(struct tempfile *tempfile, const char *template, int mode)
{
int fd;
struct strbuf full_template = STRBUF_INIT;
strbuf_add_absolute_path(&full_template, template);
fd = mks_tempfile_m(tempfile, full_template.buf, mode);
if (fd < 0)
die_errno("Unable to create temporary file '%s'",
full_template.buf);
strbuf_release(&full_template);
return fd;
}
FILE *fdopen_tempfile(struct tempfile *tempfile, const char *mode)
{
if (!tempfile->active)
die("BUG: fdopen_tempfile() called for inactive object");
if (tempfile->fp)
die("BUG: fdopen_tempfile() called for open object");
tempfile->fp = fdopen(tempfile->fd, mode);
return tempfile->fp;
}
const char *get_tempfile_path(struct tempfile *tempfile)
{
if (!tempfile->active)
die("BUG: get_tempfile_path() called for inactive object");
return tempfile->filename.buf;
}
int get_tempfile_fd(struct tempfile *tempfile)
{
if (!tempfile->active)
die("BUG: get_tempfile_fd() called for inactive object");
return tempfile->fd;
}
FILE *get_tempfile_fp(struct tempfile *tempfile)
{
if (!tempfile->active)
die("BUG: get_tempfile_fp() called for inactive object");
return tempfile->fp;
}
int close_tempfile(struct tempfile *tempfile)
{
int fd = tempfile->fd;
FILE *fp = tempfile->fp;
int err;
if (fd < 0)
return 0;
tempfile->fd = -1;
if (fp) {
tempfile->fp = NULL;
/*
* Note: no short-circuiting here; we want to fclose()
* in any case!
*/
err = ferror(fp) | fclose(fp);
} else {
err = close(fd);
}
if (err) {
int save_errno = errno;
delete_tempfile(tempfile);
errno = save_errno;
return -1;
}
return 0;
}
int reopen_tempfile(struct tempfile *tempfile)
{
if (0 <= tempfile->fd)
die("BUG: reopen_tempfile called for an open object");
if (!tempfile->active)
die("BUG: reopen_tempfile called for an inactive object");
tempfile->fd = open(tempfile->filename.buf, O_WRONLY);
return tempfile->fd;
}
int rename_tempfile(struct tempfile *tempfile, const char *path)
{
if (!tempfile->active)
die("BUG: rename_tempfile called for inactive object");
if (close_tempfile(tempfile))
return -1;
if (rename(tempfile->filename.buf, path)) {
int save_errno = errno;
delete_tempfile(tempfile);
errno = save_errno;
return -1;
}
tempfile->active = 0;
strbuf_reset(&tempfile->filename);
return 0;
}
void delete_tempfile(struct tempfile *tempfile)
{
if (!tempfile->active)
return;
if (!close_tempfile(tempfile)) {
unlink_or_warn(tempfile->filename.buf);
tempfile->active = 0;
strbuf_reset(&tempfile->filename);
}
}