[glibc] posix: Use malloc instead of alloca for the glob directory name

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=dd40146613b4cb27e6a62ece5e1153e69643e48c

commit dd40146613b4cb27e6a62ece5e1153e69643e48c
Author: Adhemerval Zanella <[email protected]>
Date:   Fri Jul 31 16:32:13 2026 +0000

    posix: Use malloc instead of alloca for the glob directory name
    
    Use malloc unconditionally instead.  These are one-off allocations
    whose cost is dwarfed by the readdir and fnmatch work that follows.
    
    The amount of stack this can take is not bounded by these calls alone,
    glob recursively calls itself per pattern component, and each call
    starts a fresh alloca budget.
    
    Checked on x86_64-linux-gnu, aarch64-linux-gnu, and i686-linux-gnu.
    
    Reviewed-by: Collin Funk <[email protected]>

Diff:
---
 posix/glob.c | 54 +++++++++++++++++++-----------------------------------
 1 file changed, 19 insertions(+), 35 deletions(-)

diff --git a/posix/glob.c b/posix/glob.c
index 17b8b90cde..a81a2285b8 100644
--- a/posix/glob.c
+++ b/posix/glob.c
@@ -557,15 +557,10 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
         }
 #endif
 
-      if (glob_use_alloca (alloca_used, dirlen + 1))
-        newp = alloca_account (dirlen + 1, alloca_used);
-      else
-        {
-          newp = malloc (dirlen + 1);
-          if (newp == NULL)
-            return GLOB_NOSPACE;
-          malloc_dirname = 1;
-        }
+      newp = malloc (dirlen + 1);
+      if (newp == NULL)
+        return GLOB_NOSPACE;
+      malloc_dirname = 1;
       *((char *) mempcpy (newp, pattern, dirlen)) = '\0';
       dirname = newp;
       ++filename;
@@ -719,19 +714,14 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
             {
               char *newp;
               size_t home_len = strlen (home_dir);
-              int use_alloca = glob_use_alloca (alloca_used, home_len + dirlen);
-              if (use_alloca)
-                newp = alloca_account (home_len + dirlen, alloca_used);
-              else
+
+              newp = malloc (home_len + dirlen);
+              if (newp == NULL)
                 {
-                  newp = malloc (home_len + dirlen);
-                  if (newp == NULL)
-                    {
-                      if (__glibc_unlikely (malloc_home_dir))
-                        free (home_dir);
-                      retval = GLOB_NOSPACE;
-                      goto out;
-                    }
+                  if (__glibc_unlikely (malloc_home_dir))
+                    free (home_dir);
+                  retval = GLOB_NOSPACE;
+                  goto out;
                 }
 
               mempcpy (mempcpy (newp, home_dir, home_len),
@@ -742,7 +732,7 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
 
               dirname = newp;
               dirlen += home_len - 1;
-              malloc_dirname = !use_alloca;
+              malloc_dirname = 1;
 
               if (__glibc_unlikely (malloc_home_dir))
                 free (home_dir);
@@ -855,21 +845,15 @@ __glob (const char *pattern, int flags, int (*errfunc) (const char *, int),
 
                 malloc_dirname = 0;
 
-                if (glob_use_alloca (alloca_used, home_len + rest_len + 1))
-                  dirname = alloca_account (home_len + rest_len + 1,
-                                            alloca_used);
-                else
+                dirname = malloc (home_len + rest_len + 1);
+                if (dirname == NULL)
                   {
-                    dirname = malloc (home_len + rest_len + 1);
-                    if (dirname == NULL)
-                      {
-                        free (prev_dirname);
-                        scratch_buffer_free (&pwtmpbuf);
-                        retval = GLOB_NOSPACE;
-                        goto out;
-                      }
-                    malloc_dirname = 1;
+                    free (prev_dirname);
+                    scratch_buffer_free (&pwtmpbuf);
+                    retval = GLOB_NOSPACE;
+                    goto out;
                   }
+                malloc_dirname = 1;
                 d = mempcpy (dirname, p->pw_dir, home_len);
                 if (end_name != NULL)
                   d = mempcpy (d, end_name, rest_len);