Revision f514ef9787f320287d7ba71f2965127b9d8b3832 authored by Jeff King on 19 August 2015, 18:12:37 UTC, committed by Junio C Hamano on 04 September 2015, 15:50:50 UTC
When unpack-trees wants to know whether a path will overwrite anything in the working tree, we use lstat() to see if there is anything there. But if we are going to write "foo/bar", we can't just lstat("foo/bar"); we need to look for leading prefixes (e.g., "foo"). So we use the lstat cache to find the length of the leading prefix, and copy the filename up to that length into a temporary buffer (since the original name is const, we cannot just stick a NUL in it). The copy we make goes into a PATH_MAX-sized buffer, which will overflow if the prefix is longer than PATH_MAX. How this happens is a little tricky, since in theory PATH_MAX is the biggest path we will have read from the filesystem. But this can happen if: - the compiled-in PATH_MAX does not accurately reflect what the filesystem is capable of - the leading prefix is not _quite_ what is on disk; it contains the next element from the name we are checking. So if we want to write "aaa/bbb/ccc/ddd" and "aaa/bbb" exists, the prefix of interest is "aaa/bbb/ccc". If "aaa/bbb" approaches PATH_MAX, then "ccc" can overflow it. So this can be triggered, but it's hard to do. In particular, you cannot just "git clone" a bogus repo. The verify_absent checks happen before unpack-trees writes anything to the filesystem, so there are never any leading prefixes during the initial checkout, and the bug doesn't trigger. And by definition, these files are larger than PATH_MAX, so writing them will fail, and clone will complain (though it may write a partial path, which will cause a subsequent "git checkout" to hit the bug). We can fix it by creating the temporary path on the heap. The extra malloc overhead is not important, as we are already making at least one stat() call (and probably more for the prefix discovery). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
1 parent fdf96a2
entry.c
#include "cache.h"
#include "blob.h"
#include "dir.h"
#include "streaming.h"
static void create_directories(const char *path, int path_len,
const struct checkout *state)
{
char *buf = xmalloc(path_len + 1);
int len = 0;
while (len < path_len) {
do {
buf[len] = path[len];
len++;
} while (len < path_len && path[len] != '/');
if (len >= path_len)
break;
buf[len] = 0;
/*
* For 'checkout-index --prefix=<dir>', <dir> is
* allowed to be a symlink to an existing directory,
* and we set 'state->base_dir_len' below, such that
* we test the path components of the prefix with the
* stat() function instead of the lstat() function.
*/
if (has_dirs_only_path(buf, len, state->base_dir_len))
continue; /* ok, it is already a directory. */
/*
* If this mkdir() would fail, it could be that there
* is already a symlink or something else exists
* there, therefore we then try to unlink it and try
* one more time to create the directory.
*/
if (mkdir(buf, 0777)) {
if (errno == EEXIST && state->force &&
!unlink_or_warn(buf) && !mkdir(buf, 0777))
continue;
die_errno("cannot create directory at '%s'", buf);
}
}
free(buf);
}
static void remove_subtree(struct strbuf *path)
{
DIR *dir = opendir(path->buf);
struct dirent *de;
int origlen = path->len;
if (!dir)
die_errno("cannot opendir '%s'", path->buf);
while ((de = readdir(dir)) != NULL) {
struct stat st;
if (is_dot_or_dotdot(de->d_name))
continue;
strbuf_addch(path, '/');
strbuf_addstr(path, de->d_name);
if (lstat(path->buf, &st))
die_errno("cannot lstat '%s'", path->buf);
if (S_ISDIR(st.st_mode))
remove_subtree(path);
else if (unlink(path->buf))
die_errno("cannot unlink '%s'", path->buf);
strbuf_setlen(path, origlen);
}
closedir(dir);
if (rmdir(path->buf))
die_errno("cannot rmdir '%s'", path->buf);
}
static int create_file(const char *path, unsigned int mode)
{
mode = (mode & 0100) ? 0777 : 0666;
return open(path, O_WRONLY | O_CREAT | O_EXCL, mode);
}
static void *read_blob_entry(const struct cache_entry *ce, unsigned long *size)
{
enum object_type type;
void *new = read_sha1_file(ce->sha1, &type, size);
if (new) {
if (type == OBJ_BLOB)
return new;
free(new);
}
return NULL;
}
static int open_output_fd(char *path, const struct cache_entry *ce, int to_tempfile)
{
int symlink = (ce->ce_mode & S_IFMT) != S_IFREG;
if (to_tempfile) {
strcpy(path, symlink
? ".merge_link_XXXXXX" : ".merge_file_XXXXXX");
return mkstemp(path);
} else {
return create_file(path, !symlink ? ce->ce_mode : 0666);
}
}
static int fstat_output(int fd, const struct checkout *state, struct stat *st)
{
/* use fstat() only when path == ce->name */
if (fstat_is_reliable() &&
state->refresh_cache && !state->base_dir_len) {
fstat(fd, st);
return 1;
}
return 0;
}
static int streaming_write_entry(const struct cache_entry *ce, char *path,
struct stream_filter *filter,
const struct checkout *state, int to_tempfile,
int *fstat_done, struct stat *statbuf)
{
int result = 0;
int fd;
fd = open_output_fd(path, ce, to_tempfile);
if (fd < 0)
return -1;
result |= stream_blob_to_fd(fd, ce->sha1, filter, 1);
*fstat_done = fstat_output(fd, state, statbuf);
result |= close(fd);
if (result)
unlink(path);
return result;
}
static int write_entry(struct cache_entry *ce,
char *path, const struct checkout *state, int to_tempfile)
{
unsigned int ce_mode_s_ifmt = ce->ce_mode & S_IFMT;
int fd, ret, fstat_done = 0;
char *new;
struct strbuf buf = STRBUF_INIT;
unsigned long size;
size_t wrote, newsize = 0;
struct stat st;
if (ce_mode_s_ifmt == S_IFREG) {
struct stream_filter *filter = get_stream_filter(ce->name, ce->sha1);
if (filter &&
!streaming_write_entry(ce, path, filter,
state, to_tempfile,
&fstat_done, &st))
goto finish;
}
switch (ce_mode_s_ifmt) {
case S_IFREG:
case S_IFLNK:
new = read_blob_entry(ce, &size);
if (!new)
return error("unable to read sha1 file of %s (%s)",
path, sha1_to_hex(ce->sha1));
if (ce_mode_s_ifmt == S_IFLNK && has_symlinks && !to_tempfile) {
ret = symlink(new, path);
free(new);
if (ret)
return error("unable to create symlink %s (%s)",
path, strerror(errno));
break;
}
/*
* Convert from git internal format to working tree format
*/
if (ce_mode_s_ifmt == S_IFREG &&
convert_to_working_tree(ce->name, new, size, &buf)) {
free(new);
new = strbuf_detach(&buf, &newsize);
size = newsize;
}
fd = open_output_fd(path, ce, to_tempfile);
if (fd < 0) {
free(new);
return error("unable to create file %s (%s)",
path, strerror(errno));
}
wrote = write_in_full(fd, new, size);
if (!to_tempfile)
fstat_done = fstat_output(fd, state, &st);
close(fd);
free(new);
if (wrote != size)
return error("unable to write file %s", path);
break;
case S_IFGITLINK:
if (to_tempfile)
return error("cannot create temporary submodule %s", path);
if (mkdir(path, 0777) < 0)
return error("cannot create submodule directory %s", path);
break;
default:
return error("unknown file mode for %s in index", path);
}
finish:
if (state->refresh_cache) {
assert(state->istate);
if (!fstat_done)
lstat(ce->name, &st);
fill_stat_cache_info(ce, &st);
ce->ce_flags |= CE_UPDATE_IN_BASE;
state->istate->cache_changed |= CE_ENTRY_CHANGED;
}
return 0;
}
/*
* This is like 'lstat()', except it refuses to follow symlinks
* in the path, after skipping "skiplen".
*/
static int check_path(const char *path, int len, struct stat *st, int skiplen)
{
const char *slash = path + len;
while (path < slash && *slash != '/')
slash--;
if (!has_dirs_only_path(path, slash - path, skiplen)) {
errno = ENOENT;
return -1;
}
return lstat(path, st);
}
/*
* Write the contents from ce out to the working tree.
*
* When topath[] is not NULL, instead of writing to the working tree
* file named by ce, a temporary file is created by this function and
* its name is returned in topath[], which must be able to hold at
* least TEMPORARY_FILENAME_LENGTH bytes long.
*/
int checkout_entry(struct cache_entry *ce,
const struct checkout *state, char *topath)
{
static struct strbuf path = STRBUF_INIT;
struct stat st;
if (topath)
return write_entry(ce, topath, state, 1);
strbuf_reset(&path);
strbuf_add(&path, state->base_dir, state->base_dir_len);
strbuf_add(&path, ce->name, ce_namelen(ce));
if (!check_path(path.buf, path.len, &st, state->base_dir_len)) {
unsigned changed = ce_match_stat(ce, &st, CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE);
if (!changed)
return 0;
if (!state->force) {
if (!state->quiet)
fprintf(stderr,
"%s already exists, no checkout\n",
path.buf);
return -1;
}
/*
* We unlink the old file, to get the new one with the
* right permissions (including umask, which is nasty
* to emulate by hand - much easier to let the system
* just do the right thing)
*/
if (S_ISDIR(st.st_mode)) {
/* If it is a gitlink, leave it alone! */
if (S_ISGITLINK(ce->ce_mode))
return 0;
if (!state->force)
return error("%s is a directory", path.buf);
remove_subtree(&path);
} else if (unlink(path.buf))
return error("unable to unlink old '%s' (%s)",
path.buf, strerror(errno));
} else if (state->not_new)
return 0;
create_directories(path.buf, path.len, state);
return write_entry(ce, path.buf, state, 0);
}
![swh spinner](/static/img/swh-spinner.gif)
Computing file changes ...