futex: Initialize futex_phash_new during fork().

During a hash resize operation the new private hash is stored in
mm_struct::futex_phash_new if the current hash can not be immediately
replaced.

The new hash must not be copied during fork() into the new task. Doing
so will lead to a double-free of the memory by the two tasks.

Initialize the mm_struct::futex_phash_new during fork().

Closes: https://lore.kernel.org/all/aFBQ8CBKmRzEqIfS@mozart.vkv.me/
Fixes: bd54df5ea7 ("futex: Allow to resize the private local hash")
Reported-by: Calvin Owens <calvin@wbinvd.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Calvin Owens <calvin@wbinvd.org>
Link: https://lkml.kernel.org/r/20250623083408.jTiJiC6_@linutronix.de

This commit is contained in:

Sebastian Andrzej Siewior

2025-06-23 10:34:08 +02:00

committed by

Peter Zijlstra

parent 86731a2a65

commit a24cc6ce19

1 changed files with 1 additions and 0 deletions

									
										include/linux/futex.h
									
		+1
		
												View File
												
				@@ -89,6 +89,7 @@ void futex_hash_free(struct mm_struct *mm);

				static inline void futex_mm_init(struct mm_struct *mm)

				{

					RCU_INIT_POINTER(mm->futex_phash, NULL);

					mm->futex_phash_new = NULL;

					mutex_init(&mm->futex_hash_lock);

				}