git/lockfile.c
Michael Haggerty 2fbd4f92fa lockfile: fix buffer overflow in path handling
The path of the file to be locked is held in lock_file::filename,
which is a fixed-length buffer of length PATH_MAX.  This buffer is
also (temporarily) used to hold the path of the lock file, which is
the path of the file being locked plus ".lock".  Because of this, the
path of the file being locked must be less than (PATH_MAX - 5)
characters long (5 chars are needed for ".lock" and one character for
the NUL terminator).

On entry into lock_file(), the path length was only verified to be
less than PATH_MAX characters, not less than (PATH_MAX - 5)
characters.

When and if resolve_symlink() is called, then that function is
correctly told to treat the buffer as (PATH_MAX - 5) characters long.
This part is correct.  However:

* If LOCK_NODEREF was specified, then resolve_symlink() is never
  called.

* If resolve_symlink() is called but the path is not a symlink, then
  the length check is never applied.

So it is possible for a path with length (PATH_MAX - 5 <= len <
PATH_MAX) to make it through the checks.  When ".lock" is strcat()ted
to such a path, the lock_file::filename buffer is overflowed.

Fix the problem by adding a check when entering lock_file() that the
original path is less than (PATH_MAX - 5) characters.

[jc: with independent development by Peff]

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2013-07-07 10:29:28 -07:00

283 lines
6.3 KiB
C

/*
* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
#include "sigchain.h"
static struct lock_file *lock_file_list;
static const char *alternate_index_output;
static void remove_lock_file(void)
{
pid_t me = getpid();
while (lock_file_list) {
if (lock_file_list->owner == me &&
lock_file_list->filename[0]) {
if (lock_file_list->fd >= 0)
close(lock_file_list->fd);
unlink_or_warn(lock_file_list->filename);
}
lock_file_list = lock_file_list->next;
}
}
static void remove_lock_file_on_signal(int signo)
{
remove_lock_file();
sigchain_pop(signo);
raise(signo);
}
/*
* p = absolute or relative path name
*
* Return a pointer into p showing the beginning of the last path name
* element. If p is empty or the root directory ("/"), just return p.
*/
static char *last_path_elm(char *p)
{
/* r starts pointing to null at the end of the string */
char *r = strchr(p, '\0');
if (r == p)
return p; /* just return empty string */
r--; /* back up to last non-null character */
/* back up past trailing slashes, if any */
while (r > p && *r == '/')
r--;
/*
* then go backwards until I hit a slash, or the beginning of
* the string
*/
while (r > p && *(r-1) != '/')
r--;
return r;
}
/* We allow "recursive" symbolic links. Only within reason, though */
#define MAXDEPTH 5
/*
* p = path that may be a symlink
* s = full size of p
*
* If p is a symlink, attempt to overwrite p with a path to the real
* file or directory (which may or may not exist), following a chain of
* symlinks if necessary. Otherwise, leave p unmodified.
*
* This is a best-effort routine. If an error occurs, p will either be
* left unmodified or will name a different symlink in a symlink chain
* that started with p's initial contents.
*
* Always returns p.
*/
static char *resolve_symlink(char *p, size_t s)
{
int depth = MAXDEPTH;
while (depth--) {
char link[PATH_MAX];
int link_len = readlink(p, link, sizeof(link));
if (link_len < 0) {
/* not a symlink anymore */
return p;
}
else if (link_len < sizeof(link))
/* readlink() never null-terminates */
link[link_len] = '\0';
else {
warning("%s: symlink too long", p);
return p;
}
if (is_absolute_path(link)) {
/* absolute path simply replaces p */
if (link_len < s)
strcpy(p, link);
else {
warning("%s: symlink too long", p);
return p;
}
} else {
/*
* link is a relative path, so I must replace the
* last element of p with it.
*/
char *r = (char *)last_path_elm(p);
if (r - p + link_len < s)
strcpy(r, link);
else {
warning("%s: symlink too long", p);
return p;
}
}
}
return p;
}
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
/*
* subtract 5 from size to make sure there's room for adding
* ".lock" for the lock file name
*/
static const size_t max_path_len = sizeof(lk->filename) - 5;
if (strlen(path) >= max_path_len)
return -1;
strcpy(lk->filename, path);
if (!(flags & LOCK_NODEREF))
resolve_symlink(lk->filename, max_path_len);
strcat(lk->filename, ".lock");
lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
if (0 <= lk->fd) {
if (!lock_file_list) {
sigchain_push_common(remove_lock_file_on_signal);
atexit(remove_lock_file);
}
lk->owner = getpid();
if (!lk->on_list) {
lk->next = lock_file_list;
lock_file_list = lk;
lk->on_list = 1;
}
if (adjust_shared_perm(lk->filename))
return error("cannot fix permission bits on %s",
lk->filename);
}
else
lk->filename[0] = 0;
return lk->fd;
}
static char *unable_to_lock_message(const char *path, int err)
{
struct strbuf buf = STRBUF_INIT;
if (err == EEXIST) {
strbuf_addf(&buf, "Unable to create '%s.lock': %s.\n\n"
"If no other git process is currently running, this probably means a\n"
"git process crashed in this repository earlier. Make sure no other git\n"
"process is running and remove the file manually to continue.",
absolute_path(path), strerror(err));
} else
strbuf_addf(&buf, "Unable to create '%s.lock': %s",
absolute_path(path), strerror(err));
return strbuf_detach(&buf, NULL);
}
int unable_to_lock_error(const char *path, int err)
{
char *msg = unable_to_lock_message(path, err);
error("%s", msg);
free(msg);
return -1;
}
NORETURN void unable_to_lock_index_die(const char *path, int err)
{
die("%s", unable_to_lock_message(path, err));
}
int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
{
int fd = lock_file(lk, path, flags);
if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
unable_to_lock_index_die(path, errno);
return fd;
}
int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
{
int fd, orig_fd;
fd = lock_file(lk, path, flags);
if (fd < 0) {
if (flags & LOCK_DIE_ON_ERROR)
unable_to_lock_index_die(path, errno);
return fd;
}
orig_fd = open(path, O_RDONLY);
if (orig_fd < 0) {
if (errno != ENOENT) {
if (flags & LOCK_DIE_ON_ERROR)
die("cannot open '%s' for copying", path);
close(fd);
return error("cannot open '%s' for copying", path);
}
} else if (copy_fd(orig_fd, fd)) {
if (flags & LOCK_DIE_ON_ERROR)
exit(128);
close(fd);
return -1;
}
return fd;
}
int close_lock_file(struct lock_file *lk)
{
int fd = lk->fd;
lk->fd = -1;
return close(fd);
}
int commit_lock_file(struct lock_file *lk)
{
char result_file[PATH_MAX];
size_t i;
if (lk->fd >= 0 && close_lock_file(lk))
return -1;
strcpy(result_file, lk->filename);
i = strlen(result_file) - 5; /* .lock */
result_file[i] = 0;
if (rename(lk->filename, result_file))
return -1;
lk->filename[0] = 0;
return 0;
}
int hold_locked_index(struct lock_file *lk, int die_on_error)
{
return hold_lock_file_for_update(lk, get_index_file(),
die_on_error
? LOCK_DIE_ON_ERROR
: 0);
}
void set_alternate_index_output(const char *name)
{
alternate_index_output = name;
}
int commit_locked_index(struct lock_file *lk)
{
if (alternate_index_output) {
if (lk->fd >= 0 && close_lock_file(lk))
return -1;
if (rename(lk->filename, alternate_index_output))
return -1;
lk->filename[0] = 0;
return 0;
}
else
return commit_lock_file(lk);
}
void rollback_lock_file(struct lock_file *lk)
{
if (lk->filename[0]) {
if (lk->fd >= 0)
close(lk->fd);
unlink_or_warn(lk->filename);
}
lk->filename[0] = 0;
}