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real_path: resolve symlinks by hand
The current implementation of real_path uses chdir() in order to resolve symlinks. Unfortunately this isn't thread-safe as chdir() affects a process as a whole and not just an individual thread. Instead perform the symlink resolution by hand so that the calls to chdir() can be removed, making real_path one step closer to being reentrant. Signed-off-by: Brandon Williams <bmwill@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Brandon Williams
Junio C Hamano
parent
8d7a455ed5
commit
05b458c104
1 changed files with 135 additions and 67 deletions
202
abspath.c
202
abspath.c
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@ -11,8 +11,45 @@ int is_directory(const char *path)
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return (!stat(path, &st) && S_ISDIR(st.st_mode));
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}
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/* removes the last path component from 'path' except if 'path' is root */
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static void strip_last_component(struct strbuf *path)
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{
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size_t offset = offset_1st_component(path->buf);
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size_t len = path->len;
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/* Find start of the last component */
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while (offset < len && !is_dir_sep(path->buf[len - 1]))
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len--;
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/* Skip sequences of multiple path-separators */
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while (offset < len && is_dir_sep(path->buf[len - 1]))
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len--;
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strbuf_setlen(path, len);
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}
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/* get (and remove) the next component in 'remaining' and place it in 'next' */
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static void get_next_component(struct strbuf *next, struct strbuf *remaining)
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{
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char *start = NULL;
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char *end = NULL;
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strbuf_reset(next);
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/* look for the next component */
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/* Skip sequences of multiple path-separators */
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for (start = remaining->buf; is_dir_sep(*start); start++)
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; /* nothing */
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/* Find end of the path component */
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for (end = start; *end && !is_dir_sep(*end); end++)
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; /* nothing */
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strbuf_add(next, start, end - start);
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/* remove the component from 'remaining' */
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strbuf_remove(remaining, 0, end - remaining->buf);
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}
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/* We allow "recursive" symbolic links. Only within reason, though. */
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#define MAXDEPTH 5
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#define MAXSYMLINKS 5
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/*
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* Return the real path (i.e., absolute path, with symlinks resolved
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@ -21,7 +58,6 @@ int is_directory(const char *path)
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* absolute_path().) The return value is a pointer to a static
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* buffer.
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*
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* The input and all intermediate paths must be shorter than MAX_PATH.
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* The directory part of path (i.e., everything up to the last
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* dir_sep) must denote a valid, existing directory, but the last
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* component need not exist. If die_on_error is set, then die with an
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@ -33,22 +69,16 @@ int is_directory(const char *path)
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*/
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static const char *real_path_internal(const char *path, int die_on_error)
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{
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static struct strbuf sb = STRBUF_INIT;
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static struct strbuf resolved = STRBUF_INIT;
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struct strbuf remaining = STRBUF_INIT;
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struct strbuf next = STRBUF_INIT;
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struct strbuf symlink = STRBUF_INIT;
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char *retval = NULL;
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/*
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* If we have to temporarily chdir(), store the original CWD
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* here so that we can chdir() back to it at the end of the
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* function:
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*/
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struct strbuf cwd = STRBUF_INIT;
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int depth = MAXDEPTH;
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char *last_elem = NULL;
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int num_symlinks = 0;
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struct stat st;
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/* We've already done it */
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if (path == sb.buf)
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if (path == resolved.buf)
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return path;
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if (!*path) {
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@ -58,74 +88,112 @@ static const char *real_path_internal(const char *path, int die_on_error)
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goto error_out;
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}
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strbuf_reset(&sb);
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strbuf_addstr(&sb, path);
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strbuf_reset(&resolved);
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while (depth--) {
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if (!is_directory(sb.buf)) {
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char *last_slash = find_last_dir_sep(sb.buf);
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if (last_slash) {
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last_elem = xstrdup(last_slash + 1);
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strbuf_setlen(&sb, last_slash - sb.buf + 1);
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} else {
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last_elem = xmemdupz(sb.buf, sb.len);
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strbuf_reset(&sb);
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}
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}
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if (sb.len) {
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if (!cwd.len && strbuf_getcwd(&cwd)) {
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if (die_on_error)
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die_errno("Could not get current working directory");
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else
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goto error_out;
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}
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if (chdir(sb.buf)) {
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if (die_on_error)
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die_errno("Could not switch to '%s'",
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sb.buf);
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else
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goto error_out;
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}
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}
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if (strbuf_getcwd(&sb)) {
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if (is_absolute_path(path)) {
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/* absolute path; start with only root as being resolved */
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int offset = offset_1st_component(path);
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strbuf_add(&resolved, path, offset);
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strbuf_addstr(&remaining, path + offset);
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} else {
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/* relative path; can use CWD as the initial resolved path */
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if (strbuf_getcwd(&resolved)) {
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if (die_on_error)
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die_errno("Could not get current working directory");
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die_errno("unable to get current working directory");
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else
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goto error_out;
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}
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strbuf_addstr(&remaining, path);
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}
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if (last_elem) {
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if (sb.len && !is_dir_sep(sb.buf[sb.len - 1]))
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strbuf_addch(&sb, '/');
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strbuf_addstr(&sb, last_elem);
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free(last_elem);
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last_elem = NULL;
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/* Iterate over the remaining path components */
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while (remaining.len > 0) {
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get_next_component(&next, &remaining);
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if (next.len == 0) {
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continue; /* empty component */
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} else if (next.len == 1 && !strcmp(next.buf, ".")) {
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continue; /* '.' component */
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} else if (next.len == 2 && !strcmp(next.buf, "..")) {
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/* '..' component; strip the last path component */
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strip_last_component(&resolved);
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continue;
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}
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if (!lstat(sb.buf, &st) && S_ISLNK(st.st_mode)) {
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struct strbuf next_sb = STRBUF_INIT;
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ssize_t len = strbuf_readlink(&next_sb, sb.buf, 0);
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if (len < 0) {
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/* append the next component and resolve resultant path */
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if (!is_dir_sep(resolved.buf[resolved.len - 1]))
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strbuf_addch(&resolved, '/');
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strbuf_addbuf(&resolved, &next);
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if (lstat(resolved.buf, &st)) {
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/* error out unless this was the last component */
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if (errno != ENOENT || remaining.len) {
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if (die_on_error)
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die_errno("Invalid symlink '%s'",
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sb.buf);
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die_errno("Invalid path '%s'",
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resolved.buf);
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else
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goto error_out;
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}
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strbuf_swap(&sb, &next_sb);
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strbuf_release(&next_sb);
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} else
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break;
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} else if (S_ISLNK(st.st_mode)) {
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ssize_t len;
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strbuf_reset(&symlink);
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if (num_symlinks++ > MAXSYMLINKS) {
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if (die_on_error)
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die("More than %d nested symlinks "
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"on path '%s'", MAXSYMLINKS, path);
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else
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goto error_out;
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}
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len = strbuf_readlink(&symlink, resolved.buf,
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st.st_size);
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if (len < 0) {
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if (die_on_error)
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die_errno("Invalid symlink '%s'",
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resolved.buf);
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else
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goto error_out;
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}
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if (is_absolute_path(symlink.buf)) {
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/* absolute symlink; set resolved to root */
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int offset = offset_1st_component(symlink.buf);
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strbuf_reset(&resolved);
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strbuf_add(&resolved, symlink.buf, offset);
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strbuf_remove(&symlink, 0, offset);
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} else {
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/*
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* relative symlink
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* strip off the last component since it will
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* be replaced with the contents of the symlink
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*/
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strip_last_component(&resolved);
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}
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/*
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* if there are still remaining components to resolve
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* then append them to symlink
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*/
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if (remaining.len) {
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strbuf_addch(&symlink, '/');
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strbuf_addbuf(&symlink, &remaining);
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}
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/*
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* use the symlink as the remaining components that
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* need to be resloved
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*/
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strbuf_swap(&symlink, &remaining);
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}
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}
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retval = sb.buf;
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retval = resolved.buf;
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error_out:
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free(last_elem);
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if (cwd.len && chdir(cwd.buf))
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die_errno("Could not change back to '%s'", cwd.buf);
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strbuf_release(&cwd);
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strbuf_release(&remaining);
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strbuf_release(&next);
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strbuf_release(&symlink);
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return retval;
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}
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