Commit a24cc6ce authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Peter Zijlstra
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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: bd54df5e ("futex: Allow to resize the private local hash")
Reported-by: default avatarCalvin Owens <calvin@wbinvd.org>
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarCalvin Owens <calvin@wbinvd.org>
Link: https://lkml.kernel.org/r/20250623083408.jTiJiC6_@linutronix.de
parent 86731a2a

include/linux/futex.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

}