From 3919600d32b92e67f1d28376bd63152306e99452 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Wed, 30 Apr 2025 09:58:05 +0200 Subject: [PATCH] s390/mm: Fix potential use-after-free in __crst_table_upgrade() The pointer to the mm_struct which is passed to __crst_table_upgrade() may only be dereferenced if it is identical to current->active_mm. Otherwise the current task has no reference to the mm_struct and it may already be freed. In such a case this would result in a use-after-free bug. Make sure this use-after-free scenario does not happen by moving the code, which dereferences the mm_struct pointer, after the check which verifies that the pointer is identical to current->active_mm, like it was before lazy ASCE handling was reimplemented. Fixes: 8b72f5a97b82 ("s390/mm: Reimplement lazy ASCE handling") Reviewed-by: Gerald Schaefer Signed-off-by: Heiko Carstens --- arch/s390/mm/pgalloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c index e33903b419a9..d177bea0bd73 100644 --- a/arch/s390/mm/pgalloc.c +++ b/arch/s390/mm/pgalloc.c @@ -40,9 +40,9 @@ static void __crst_table_upgrade(void *arg) struct mm_struct *mm = arg; struct ctlreg asce; - asce.val = mm->context.asce; /* change all active ASCEs to avoid the creation of new TLBs */ if (current->active_mm == mm) { + asce.val = mm->context.asce; get_lowcore()->user_asce = asce; local_ctl_load(7, &asce); if (!test_thread_flag(TIF_ASCE_PRIMARY))