[glibc] posix: Remove the alloca uses from glob_in_dir

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6288139c32a194e0005593c30af6c79bb698cdf2

commit 6288139c32a194e0005593c30af6c79bb698cdf2
Author: Adhemerval Zanella <[email protected]>
Date:   Fri Jul 31 18:07:44 2026 +0000

    posix: Remove the alloca uses from glob_in_dir
    
    What is left are the name used to stat a component without
    metacharacters and the blocks holding the matched names.  With those on
    the heap the alloca budget can go as well.
    
    Also treat the size overflow as an error.  It used to fall through
    to malloc with the wrapped size and then copy the full length
    into it.
    
    alloca is now used only by the MSDOS and Windows paths, which glibc
    does not build, so move its header out of the way as well.
    
    Checked on x86_64-linux-gnu, aarch64-linux-gnu, and i686-linux-gnu.
    
    Reviewed-by: Collin Funk <[email protected]>

Diff:
---
 posix/glob.c | 68 +++++++++++++++---------------------------------------------
 1 file changed, 17 insertions(+), 51 deletions(-)

diff --git a/posix/glob.c b/posix/glob.c
index f1380cf596..c1179c7f5d 100644
--- a/posix/glob.c
+++ b/posix/glob.c
@@ -49,7 +49,6 @@
 #include <dirent.h>
 #include <stdlib.h>
 #include <string.h>
-#include <alloca.h>
 
 #ifdef _LIBC
 # undef strdup
@@ -183,6 +182,8 @@ convert_dirent64 (const struct dirent64 *source)
 #endif
 
 #ifndef _LIBC
+# include <alloca.h>
+
 /* The results of opendir() in this file are not used with dirfd and fchdir,
    and we do not leak fds to any single-threaded code that could use stdio,
    therefore save some unnecessary recursion in fchdir.c and opendir_safer.c.
@@ -194,12 +195,6 @@ convert_dirent64 (const struct dirent64 *source)
 # ifdef GNULIB_defined_closedir
 #  undef closedir
 # endif
-
-/* Just use malloc.  */
-# define __libc_use_alloca(n) false
-# define alloca_account(len, avar) ((void) (len), (void) (avar), (void *) 0)
-# define extend_alloca_account(buf, len, newlen, avar) \
-    ((void) (buf), (void) (len), (void) (newlen), (void) (avar), (void *) 0)
 #endif
 
 static int
@@ -233,17 +228,9 @@ size_add_wrapv (size_t a, size_t b, size_t *r)
 #endif
 }
 
-static bool
-glob_use_alloca (size_t alloca_used, size_t len)
-{
-  size_t size;
-  return (!size_add_wrapv (alloca_used, len, &size)
-          && __libc_use_alloca (size));
-}
-
 static int glob_in_dir (const char *pattern, const char *directory,
                         int flags, int (*errfunc) (const char *, int),
-                        glob_t *pglob, size_t alloca_used);
+                        glob_t *pglob);
 static int prefix_array (const char *prefix, char **array, size_t n) __THROWNL;
 static int collated_compare (const void *, const void *) __THROWNL;
 
@@ -407,7 +394,6 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
   int malloc_dirname = 0;
   glob_t dirs;
   int retval = 0;
-  size_t alloca_used = 0;
 
   if (pattern == NULL || pglob == NULL || (flags & ~__GLOB_FLAGS) != 0)
     {
@@ -1046,7 +1032,7 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
           status = glob_in_dir (filename, dirs.gl_pathv[i],
                                 ((flags | GLOB_APPEND)
                                  & ~(GLOB_NOCHECK | GLOB_NOMAGIC)),
-                                errfunc, pglob, alloca_used);
+                                errfunc, pglob);
           if (status == GLOB_NOMATCH)
             /* No matches in this directory.  Try the next.  */
             continue;
@@ -1155,8 +1141,7 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
         }
       if (dirname_modified)
         flags &= ~(GLOB_NOCHECK | GLOB_NOMAGIC);
-      status = glob_in_dir (filename, dirname, flags, errfunc, pglob,
-                            alloca_used);
+      status = glob_in_dir (filename, dirname, flags, errfunc, pglob);
       if (status != 0)
         {
           if (status == GLOB_NOMATCH && flags != orig_flags
@@ -1305,8 +1290,7 @@ prefix_array (const char *dirname, char **array, size_t n)
    The GLOB_APPEND flag is assumed to be set (always appends).  */
 static int
 glob_in_dir (const char *pattern, const char *directory, int flags,
-             int (*errfunc) (const char *, int),
-             glob_t *pglob, size_t alloca_used)
+             int (*errfunc) (const char *, int), glob_t *pglob)
 {
   size_t dirlen = strlen (directory);
   void *stream = NULL;
@@ -1318,15 +1302,12 @@ glob_in_dir (const char *pattern, const char *directory, int flags,
   struct { GLOBNAMES_MEMBERS (64) } init_names_buf;
   struct globnames *init_names = (struct globnames *) &init_names_buf;
   struct globnames *names = init_names;
-  struct globnames *names_alloca = init_names;
   size_t nfound = 0;
   size_t cur = 0;
   int meta;
   int save;
   int result;
 
-  alloca_used += sizeof init_names_buf;
-
   init_names->next = NULL;
   init_names->count = ((sizeof init_names_buf
                         - offsetof (struct globnames, name))
@@ -1344,18 +1325,13 @@ glob_in_dir (const char *pattern, const char *directory, int flags,
     {
       size_t patlen = strlen (pattern);
       size_t fullsize;
-      bool alloca_fullname
-        = (! size_add_wrapv (dirlen + 1, patlen + 1, &fullsize)
-           && glob_use_alloca (alloca_used, fullsize));
       char *fullname;
-      if (alloca_fullname)
-        fullname = alloca_account (fullsize, alloca_used);
-      else
-        {
-          fullname = malloc (fullsize);
-          if (fullname == NULL)
-            return GLOB_NOSPACE;
-        }
+
+      if (size_add_wrapv (dirlen + 1, patlen + 1, &fullsize))
+        return GLOB_NOSPACE;
+      fullname = malloc (fullsize);
+      if (fullname == NULL)
+        return GLOB_NOSPACE;
 
       mempcpy (mempcpy (mempcpy (fullname, directory, dirlen),
                         "/", 1),
@@ -1366,8 +1342,7 @@ glob_in_dir (const char *pattern, const char *directory, int flags,
            of the function to copy this name into the result.  */
         flags |= GLOB_NOCHECK;
 
-      if (__glibc_unlikely (!alloca_fullname))
-        free (fullname);
+      free (fullname);
     }
   else
     {
@@ -1451,11 +1426,8 @@ glob_in_dir (const char *pattern, const char *directory, int flags,
                       if ((SIZE_MAX - nameoff) / 2 / sizeof (char *)
                           < names->count)
                         goto memory_error;
-                      if (glob_use_alloca (alloca_used, size))
-                        newnames = names_alloca
-                          = alloca_account (size, alloca_used);
-                      else if ((newnames = malloc (size))
-                               == NULL)
+                      newnames = malloc (size);
+                      if (newnames == NULL)
                         goto memory_error;
                       newnames->count = count;
                       newnames->next = names;
@@ -1518,10 +1490,7 @@ glob_in_dir (const char *pattern, const char *directory, int flags,
                   break;
                 }
               cur = names->count;
-              if (old == names_alloca)
-                names_alloca = names;
-              else
-                free (old);
+              free (old);
             }
           result = GLOB_NOSPACE;
         }
@@ -1544,10 +1513,7 @@ glob_in_dir (const char *pattern, const char *directory, int flags,
                   break;
                 }
               cur = names->count;
-              if (old == names_alloca)
-                names_alloca = names;
-              else
-                free (old);
+              free (old);
             }
 
           pglob->gl_pathv = new_gl_pathv;