diff mbox series

[RFC,1/2] elf: Port ldconfig away from stack-allocated paths

Message ID 20230517185422.71084-2-bugaevc@gmail.com
State Superseded
Headers
Series On ldconfig and ld.so.cache |

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent

Commit Message

Sergey Bugaev May 17, 2023, 6:54 p.m. UTC 
  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 <bugaevc@gmail.com>
---
 elf/ldconfig.c | 59 +++++++++++++++++---------------------------------
 1 file changed, 20 insertions(+), 39 deletions(-)

Comments

Adhemerval Zanella May 18, 2023, 7:13 p.m. UTC | #1 
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 <bugaevc@gmail.com>

Sounds reasonable and one less alloca usage.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@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);
Florian Weimer May 19, 2023, 12:25 p.m. UTC | #2 
* Sergey Bugaev via Libc-alpha:

> @@ -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.  */

Missing error checking?

I think we use x* functions such a xstrdup elsewhere in ldconfig, so you
could add xasprintf as well.

Thanks,
Florian
Sergey Bugaev May 20, 2023, 7:03 p.m. UTC | #3 
Hello,

On Fri, May 19, 2023 at 3:25 PM Florian Weimer <fweimer@redhat.com> wrote:
> Missing error checking?

Indeed, thanks. Fixed.

> I think we use x* functions such a xstrdup elsewhere in ldconfig, so you
> could add xasprintf as well.

Apparently the existing code didn't #include <support/support.h> and link
to libsupport (xstrdup must be coming from somewhere else.) I opted to
check for asprintf returning < 0 and calling error () explicitly instead,
like other code in this same file does already.

Sergey

-- >8 --
Subject: [PATCH 1/2 v2] elf: Port ldconfig away from stack-allocated paths

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.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
 elf/ldconfig.c | 60 +++++++++++++++++++-------------------------------
 1 file changed, 23 insertions(+), 37 deletions(-)

diff --git a/elf/ldconfig.c b/elf/ldconfig.c
index 2fc45ad8..e643dd57 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 +723,16 @@ 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);
+      if (asprintf (&file_name, "%s/%s", entry->path, direntry->d_name) < 0)
+	error (EXIT_FAILURE, errno, _("Could not form library path"));
       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);
+	  if (asprintf (&real_file_name, "%s/%s",
+			dir_name, direntry->d_name) < 0)
+	    error (EXIT_FAILURE, errno, _("Could not form library path"));
 	}
+      else
+	real_file_name = file_name;
 
       struct stat lstat_buf;
       /* We optimize and try to do the lstat call only if needed.  */
@@ -761,7 +742,7 @@ 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 +759,7 @@ 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 +774,7 @@ search_dir (const struct dir_entry *entry)
 	      if (opt_chroot != NULL)
 		free (target_name);
 
-	      continue;
+	      goto next;
 	    }
 
 	  if (opt_chroot != NULL)
@@ -806,7 +787,7 @@ 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 +797,7 @@ 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 +809,7 @@ 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 +823,7 @@ 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 +929,11 @@ 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);
Adhemerval Zanella May 23, 2023, 5:57 p.m. UTC | #4 
On 20/05/23 16:03, Sergey Bugaev wrote:
> Hello,
> 
> On Fri, May 19, 2023 at 3:25 PM Florian Weimer <fweimer@redhat.com> wrote:
>> Missing error checking?
> 
> Indeed, thanks. Fixed.
> 
>> I think we use x* functions such a xstrdup elsewhere in ldconfig, so you
>> could add xasprintf as well.
> 
> Apparently the existing code didn't #include <support/support.h> and link
> to libsupport (xstrdup must be coming from somewhere else.) I opted to
> check for asprintf returning < 0 and calling error () explicitly instead,
> like other code in this same file does already.
> 
> Sergey
> 
> -- >8 --
> Subject: [PATCH 1/2 v2] elf: Port ldconfig away from stack-allocated paths
> 
> 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.
> 
> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>

Still looks good to me, thanks.

> ---
>  elf/ldconfig.c | 60 +++++++++++++++++++-------------------------------
>  1 file changed, 23 insertions(+), 37 deletions(-)
> 
> diff --git a/elf/ldconfig.c b/elf/ldconfig.c
> index 2fc45ad8..e643dd57 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 +723,16 @@ 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);
> +      if (asprintf (&file_name, "%s/%s", entry->path, direntry->d_name) < 0)
> +	error (EXIT_FAILURE, errno, _("Could not form library path"));
>        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);
> +	  if (asprintf (&real_file_name, "%s/%s",
> +			dir_name, direntry->d_name) < 0)
> +	    error (EXIT_FAILURE, errno, _("Could not form library path"));
>  	}
> +      else
> +	real_file_name = file_name;
>  
>        struct stat lstat_buf;
>        /* We optimize and try to do the lstat call only if needed.  */
> @@ -761,7 +742,7 @@ 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 +759,7 @@ 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 +774,7 @@ search_dir (const struct dir_entry *entry)
>  	      if (opt_chroot != NULL)
>  		free (target_name);
>  
> -	      continue;
> +	      goto next;
>  	    }
>  
>  	  if (opt_chroot != NULL)
> @@ -806,7 +787,7 @@ 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 +797,7 @@ 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 +809,7 @@ 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 +823,7 @@ 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 +929,11 @@ 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);
Florian Weimer May 25, 2023, 8:07 a.m. UTC | #5 
* Sergey Bugaev:

> diff --git a/elf/ldconfig.c b/elf/ldconfig.c
> index 2fc45ad8..e643dd57 100644
> --- a/elf/ldconfig.c
> +++ b/elf/ldconfig.c

> -	  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);
> +	  if (asprintf (&real_file_name, "%s/%s",
> +			dir_name, direntry->d_name) < 0)
> +	    error (EXIT_FAILURE, errno, _("Could not form library path"));
>  	}
> +      else
> +	real_file_name = file_name;

Maybe use xstrdup (file_name) here and free unconditionally below?
It makes it easier to analyze the code for use-after-free errors.

Rest looks okay.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian
diff mbox series

Patch

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);