On 17/05/23 15:54, Sergey Bugaev via Libc-alpha wrote:
> ldconfig was allocating PATH_MAX bytes on the stack for the library file
> name. The issues with PATH_MAX usage are well documented [0][1]; even if
> a program does not rely on paths being limited to PATH_MAX bytes,
> allocating 4096 bytes on the stack for paths that are typically rather
> short (strlen ("/lib64/libc.so.6") is 16) is wasteful and dangerous.
>
> [0]: https://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html
> [1]: https://eklitzke.org/path-max-is-tricky
>
> Instead, make use of asprintf to dynamically allocate memory of just the
> right size on the heap.
>
> Checked on x86_64-linux-gnu and i686-gnu.
>
> Signed-off-by: Sergey Bugaev <buga...@gmail.com>
Sounds reasonable and one less alloca usage.
Reviewed-by: Adhemerval Zanella <adhemerval.zane...@linaro.org>
> ---
> elf/ldconfig.c | 59 +++++++++++++++++---------------------------------
> 1 file changed, 20 insertions(+), 39 deletions(-)
>
> diff --git a/elf/ldconfig.c b/elf/ldconfig.c
> index 2fc45ad8..7f2e4226 100644
> --- a/elf/ldconfig.c
> +++ b/elf/ldconfig.c
> @@ -677,28 +677,18 @@ search_dir (const struct dir_entry *entry)
>
> char *dir_name;
> char *real_file_name;
> - size_t real_file_name_len;
> - size_t file_name_len = PATH_MAX;
> - char *file_name = alloca (file_name_len);
> + char *file_name;
> if (opt_chroot != NULL)
> - {
> - dir_name = chroot_canon (opt_chroot, entry->path);
> - real_file_name_len = PATH_MAX;
> - real_file_name = alloca (real_file_name_len);
> - }
> + dir_name = chroot_canon (opt_chroot, entry->path);
> else
> - {
> - dir_name = entry->path;
> - real_file_name_len = 0;
> - real_file_name = file_name;
> - }
> + dir_name = entry->path;
>
> DIR *dir;
> if (dir_name == NULL || (dir = opendir (dir_name)) == NULL)
> {
> if (opt_verbose)
> error (0, errno, _("Can't open directory %s"), entry->path);
> - if (opt_chroot != NULL && dir_name != NULL)
> + if (opt_chroot != NULL)
> free (dir_name);
> return;
> }
> @@ -733,25 +723,11 @@ search_dir (const struct dir_entry *entry)
> + 1, ".#prelink#.", sizeof (".#prelink#.") - 1) == 0)
> continue;
> }
> - len += strlen (entry->path) + 2;
> - if (len > file_name_len)
> - {
> - file_name_len = len;
> - file_name = alloca (file_name_len);
> - if (!opt_chroot)
> - real_file_name = file_name;
> - }
> - sprintf (file_name, "%s/%s", entry->path, direntry->d_name);
> + asprintf (&file_name, "%s/%s", entry->path, direntry->d_name);
> if (opt_chroot != NULL)
> - {
> - len = strlen (dir_name) + strlen (direntry->d_name) + 2;
> - if (len > real_file_name_len)
> - {
> - real_file_name_len = len;
> - real_file_name = alloca (real_file_name_len);
> - }
> - sprintf (real_file_name, "%s/%s", dir_name, direntry->d_name);
> - }
> + asprintf (&real_file_name, "%s/%s", dir_name, direntry->d_name);
> + else
> + real_file_name = file_name;
>
> struct stat lstat_buf;
> /* We optimize and try to do the lstat call only if needed. */
> @@ -761,7 +737,7 @@ search_dir (const struct dir_entry *entry)
> if (__glibc_unlikely (lstat (real_file_name, &lstat_buf)))
> {
> error (0, errno, _("Cannot lstat %s"), file_name);
> - continue;
> + goto next;
> }
>
> struct stat stat_buf;
> @@ -778,7 +754,7 @@ search_dir (const struct dir_entry *entry)
> {
> if (strstr (file_name, ".so") == NULL)
> error (0, 0, _("Input file %s not found.\n"), file_name);
> - continue;
> + goto next;
> }
> }
> if (__glibc_unlikely (stat (target_name, &stat_buf)))
> @@ -793,7 +769,7 @@ search_dir (const struct dir_entry *entry)
> if (opt_chroot != NULL)
> free (target_name);
>
> - continue;
> + goto next;
> }
>
> if (opt_chroot != NULL)
> @@ -806,7 +782,7 @@ search_dir (const struct dir_entry *entry)
> lstat_buf.st_ctime = stat_buf.st_ctime;
> }
> else if (!S_ISREG (lstat_buf.st_mode))
> - continue;
> + goto next;
>
> char *real_name;
> if (opt_chroot != NULL && is_link)
> @@ -816,7 +792,7 @@ search_dir (const struct dir_entry *entry)
> {
> if (strstr (file_name, ".so") == NULL)
> error (0, 0, _("Input file %s not found.\n"), file_name);
> - continue;
> + goto next;
> }
> }
> else
> @@ -828,7 +804,7 @@ search_dir (const struct dir_entry *entry)
> && __builtin_expect (lstat (real_file_name, &lstat_buf), 0))
> {
> error (0, errno, _("Cannot lstat %s"), file_name);
> - continue;
> + goto next;
> }
>
> /* First search whether the auxiliary cache contains this
> @@ -842,7 +818,7 @@ search_dir (const struct dir_entry *entry)
> {
> if (real_name != real_file_name)
> free (real_name);
> - continue;
> + goto next;
> }
> else if (opt_build_cache)
> add_to_aux_cache (&lstat_buf, flag, isa_level, soname);
> @@ -948,6 +924,11 @@ search_dir (const struct dir_entry *entry)
> dlib_ptr->next = dlibs;
> dlibs = dlib_ptr;
> }
> +
> + next:
> + free (file_name);
> + if (opt_chroot != NULL)
> + free (real_file_name);
> }
>
> closedir (dir);
