From 05b458c104708141d2fad211d79703b3b99cc5a8 Mon Sep 17 00:00:00 2001 From: Brandon Williams Date: Mon, 12 Dec 2016 10:16:52 -0800 Subject: [PATCH] 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 Signed-off-by: Junio C Hamano --- abspath.c | 202 ++++++++++++++++++++++++++++++++++++------------------ 1 file changed, 135 insertions(+), 67 deletions(-) diff --git a/abspath.c b/abspath.c index 2825de8591..cafcae0352 100644 --- a/abspath.c +++ b/abspath.c @@ -11,8 +11,45 @@ int is_directory(const char *path) return (!stat(path, &st) && S_ISDIR(st.st_mode)); } +/* removes the last path component from 'path' except if 'path' is root */ +static void strip_last_component(struct strbuf *path) +{ + size_t offset = offset_1st_component(path->buf); + size_t len = path->len; + + /* Find start of the last component */ + while (offset < len && !is_dir_sep(path->buf[len - 1])) + len--; + /* Skip sequences of multiple path-separators */ + while (offset < len && is_dir_sep(path->buf[len - 1])) + len--; + + strbuf_setlen(path, len); +} + +/* get (and remove) the next component in 'remaining' and place it in 'next' */ +static void get_next_component(struct strbuf *next, struct strbuf *remaining) +{ + char *start = NULL; + char *end = NULL; + + strbuf_reset(next); + + /* look for the next component */ + /* Skip sequences of multiple path-separators */ + for (start = remaining->buf; is_dir_sep(*start); start++) + ; /* nothing */ + /* Find end of the path component */ + for (end = start; *end && !is_dir_sep(*end); end++) + ; /* nothing */ + + strbuf_add(next, start, end - start); + /* remove the component from 'remaining' */ + strbuf_remove(remaining, 0, end - remaining->buf); +} + /* We allow "recursive" symbolic links. Only within reason, though. */ -#define MAXDEPTH 5 +#define MAXSYMLINKS 5 /* * Return the real path (i.e., absolute path, with symlinks resolved @@ -21,7 +58,6 @@ int is_directory(const char *path) * absolute_path().) The return value is a pointer to a static * buffer. * - * The input and all intermediate paths must be shorter than MAX_PATH. * The directory part of path (i.e., everything up to the last * dir_sep) must denote a valid, existing directory, but the last * component need not exist. If die_on_error is set, then die with an @@ -33,22 +69,16 @@ int is_directory(const char *path) */ static const char *real_path_internal(const char *path, int die_on_error) { - static struct strbuf sb = STRBUF_INIT; + static struct strbuf resolved = STRBUF_INIT; + struct strbuf remaining = STRBUF_INIT; + struct strbuf next = STRBUF_INIT; + struct strbuf symlink = STRBUF_INIT; char *retval = NULL; - - /* - * If we have to temporarily chdir(), store the original CWD - * here so that we can chdir() back to it at the end of the - * function: - */ - struct strbuf cwd = STRBUF_INIT; - - int depth = MAXDEPTH; - char *last_elem = NULL; + int num_symlinks = 0; struct stat st; /* We've already done it */ - if (path == sb.buf) + if (path == resolved.buf) return path; if (!*path) { @@ -58,74 +88,112 @@ static const char *real_path_internal(const char *path, int die_on_error) goto error_out; } - strbuf_reset(&sb); - strbuf_addstr(&sb, path); + strbuf_reset(&resolved); - while (depth--) { - if (!is_directory(sb.buf)) { - char *last_slash = find_last_dir_sep(sb.buf); - if (last_slash) { - last_elem = xstrdup(last_slash + 1); - strbuf_setlen(&sb, last_slash - sb.buf + 1); - } else { - last_elem = xmemdupz(sb.buf, sb.len); - strbuf_reset(&sb); - } - } - - if (sb.len) { - if (!cwd.len && strbuf_getcwd(&cwd)) { - if (die_on_error) - die_errno("Could not get current working directory"); - else - goto error_out; - } - - if (chdir(sb.buf)) { - if (die_on_error) - die_errno("Could not switch to '%s'", - sb.buf); - else - goto error_out; - } - } - if (strbuf_getcwd(&sb)) { + if (is_absolute_path(path)) { + /* absolute path; start with only root as being resolved */ + int offset = offset_1st_component(path); + strbuf_add(&resolved, path, offset); + strbuf_addstr(&remaining, path + offset); + } else { + /* relative path; can use CWD as the initial resolved path */ + if (strbuf_getcwd(&resolved)) { if (die_on_error) - die_errno("Could not get current working directory"); + die_errno("unable to get current working directory"); else goto error_out; } + strbuf_addstr(&remaining, path); + } - if (last_elem) { - if (sb.len && !is_dir_sep(sb.buf[sb.len - 1])) - strbuf_addch(&sb, '/'); - strbuf_addstr(&sb, last_elem); - free(last_elem); - last_elem = NULL; + /* Iterate over the remaining path components */ + while (remaining.len > 0) { + get_next_component(&next, &remaining); + + if (next.len == 0) { + continue; /* empty component */ + } else if (next.len == 1 && !strcmp(next.buf, ".")) { + continue; /* '.' component */ + } else if (next.len == 2 && !strcmp(next.buf, "..")) { + /* '..' component; strip the last path component */ + strip_last_component(&resolved); + continue; } - if (!lstat(sb.buf, &st) && S_ISLNK(st.st_mode)) { - struct strbuf next_sb = STRBUF_INIT; - ssize_t len = strbuf_readlink(&next_sb, sb.buf, 0); - if (len < 0) { + /* append the next component and resolve resultant path */ + if (!is_dir_sep(resolved.buf[resolved.len - 1])) + strbuf_addch(&resolved, '/'); + strbuf_addbuf(&resolved, &next); + + if (lstat(resolved.buf, &st)) { + /* error out unless this was the last component */ + if (errno != ENOENT || remaining.len) { if (die_on_error) - die_errno("Invalid symlink '%s'", - sb.buf); + die_errno("Invalid path '%s'", + resolved.buf); else goto error_out; } - strbuf_swap(&sb, &next_sb); - strbuf_release(&next_sb); - } else - break; + } else if (S_ISLNK(st.st_mode)) { + ssize_t len; + strbuf_reset(&symlink); + + if (num_symlinks++ > MAXSYMLINKS) { + if (die_on_error) + die("More than %d nested symlinks " + "on path '%s'", MAXSYMLINKS, path); + else + goto error_out; + } + + len = strbuf_readlink(&symlink, resolved.buf, + st.st_size); + if (len < 0) { + if (die_on_error) + die_errno("Invalid symlink '%s'", + resolved.buf); + else + goto error_out; + } + + if (is_absolute_path(symlink.buf)) { + /* absolute symlink; set resolved to root */ + int offset = offset_1st_component(symlink.buf); + strbuf_reset(&resolved); + strbuf_add(&resolved, symlink.buf, offset); + strbuf_remove(&symlink, 0, offset); + } else { + /* + * relative symlink + * strip off the last component since it will + * be replaced with the contents of the symlink + */ + strip_last_component(&resolved); + } + + /* + * if there are still remaining components to resolve + * then append them to symlink + */ + if (remaining.len) { + strbuf_addch(&symlink, '/'); + strbuf_addbuf(&symlink, &remaining); + } + + /* + * use the symlink as the remaining components that + * need to be resloved + */ + strbuf_swap(&symlink, &remaining); + } } - retval = sb.buf; + retval = resolved.buf; + error_out: - free(last_elem); - if (cwd.len && chdir(cwd.buf)) - die_errno("Could not change back to '%s'", cwd.buf); - strbuf_release(&cwd); + strbuf_release(&remaining); + strbuf_release(&next); + strbuf_release(&symlink); return retval; }