From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794633951; b=MpQpAtF8l87zMmwW/QfAcVX3Cal9JsdS0v+tFavt01uvV7sFYFb+BsNNxNUxvqlDYeQI 9Z+wdTc81rRyGFMDs8S5huHu96CVSR16qpkD6hG6ZwJCkr9329M0fivUem8sH95bwn8Pc N4mGqJCwj2AW3nKBTXAWIrkfFs+RbXMBO8duinUNRpmGcQTJo9ID2t6RmYb7joIn5BnR0 FGitbszQsDB0hI+2cUTiKqt3KxMs9UdPKtWARucDudd1Fk6eA1e1saxtsV59YJdhdR8LC Rm++7PzYOJvBOT5Ft87M1T1GqxCeb7+lzUhGrva2cluPN1krK9Qi/wGmreiEiDWANWA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794633951; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=Pt00E6EePNE8b8GKdGufzELxtl6phO/EBWMq4zxuXP4=; b=2u4s0NfG5Qp2jfAWIV4krhaOg/+2mHJZ3CB7vviChTW2uNA9Jd3c1gkFDMiLxYQ+QwpD lh8KWyyuu5Rq+Pmi6wcilS4jP1j9KNPqfecoRsfPwqCgq7OszbPoU7FGD2mqWO5QPj5X6 gTw5dtKTETcDvITICQ3qeiRbauJNcj+A++bGlFGcUn8fjj2nJrrs2nIMrii/IpQWdccB5 n6iElt5lE6+jLqxBVQ4MlJk3p1IY97v9MYqQnXvCp8MKeksbzpbkydBnSlDYIexHGsDTb LVxP1jPOBNCF/hnw/a7pUs6FCU7QI7jh5epxj/vYDSS7A3VXlws93Vx2RVLR+c/mg7A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LxLOZiAG; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F0045606A332 for ; Sat, 14 Nov 2026 05:25:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LxLOZiAG Received: by smtp.kernel.org (Postfix) with ESMTPSA id 457701F000C4; Sat, 14 Nov 2026 05:25:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794633950; bh=Pt00E6EePNE8b8GKdGufzELxtl6phO/EBWMq4zxuXP4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=LxLOZiAG/eiMuSDo9y8qhQARdH38Q6HZbPeo3guOpGo3ymPhJhn1itN4lWKAja1AG k8aNLGKOnrdIa2xluxmzk5dQls5fJWH6r7qXSPfM1DoIYkJYSegmEhkY7BHH53nw45 yKUAbNp5Tw1TZywvGNjirtAY1++H5TKiqSkRP71MZYde7UE4o3JRUFZqbXSQKr/SqE Y5jUe5geuVZsyydAK3v3PLGnLkINtlSGCK+rZD+xgFraTFEb8IfIFdDgg8zDQv7/Xv +Lmmed2Gg+Sbf/RifYRdziHUUh5fus9mKva2d5IiOJWisfOpDzkiUWBPePGWKUZ8fb Nkqjw+geUHKcw== From: Sasha Levin To: stable@vger.kernel.org Cc: "David Hildenbrand (Arm)" , Josef Bacik , "Lorenzo Stoakes (ARM)" , Rik van Riel , "Vlastimil Babka (SUSE)" , Barry Song , Pedro Falcato , "Harry Yoo (Meta)" , "Kiryl Shutsemau (Meta)" , SJ Park , Muhammad Usama Anjum , Sasha Levin Subject: [PATCH 6.12.y] fork: take mmap_lock before copying mm_struct Date: Sat, 14 Nov 2026 00:25:47 -0500 Message-ID: <20261114052533.3081626-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109200703-failed-6.12-ef694e2d2101@kernel.org> References: <20261109200703-failed-6.12-ef694e2d2101@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "David Hildenbrand (Arm)" [ Upstream commit ef694e2d210111cc08c52fd25da9ab130170bfa3 ] dup_mm() copies the parent's mm_struct before dup_mmap() takes the mmap_lock. A concurrent brk() can leave the child with a stale mm->brk and newer heap mappings, causing later brk() requests to fail. Other operations (e.g., PR_SET_MM) on the parent's mm_struct can similarly cause inconsistencies. As a simple and robust fix, grab the parent's mmap_lock earlier. This way we don't need to update individual mm fields in dup_mmap() and keep missing ones. Stop updating the 4 existing members (total_vm, data_vm, exec_vm, stack_vm), as that is now no longer required. Keep releasing the parent's mmap_lock in dup_mmap(), before userfaultfd completion, to avoid moving the userfaultfd handling into the caller. This should get cleaned up later. Move uprobe_start_dup_mmap() to preserve the lock ordering. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Reported-by: Josef Bacik Reviewed-by: Lorenzo Stoakes (ARM) Reviewed-by: Rik van Riel Reviewed-by: Vlastimil Babka (SUSE) Reviewed-by: Barry Song Reviewed-by: Pedro Falcato Reviewed-by: Harry Yoo (Meta) Reviewed-by: Kiryl Shutsemau (Meta) Reviewed-by: SJ Park Tested-by: Muhammad Usama Anjum Link: https://patch.msgid.link/20261031-fixes_core-v3-2-d6437171ecc3@kernel.org Signed-off-by: David Hildenbrand (Arm) [ sashal: Retained mm->user_ns as the third argument to mm_init(). ] Signed-off-by: Sasha Levin --- kernel/fork.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 140a615daf42e..af3c8be386efa 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -641,8 +641,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, LIST_HEAD(uf); VMA_ITERATOR(vmi, mm, 0); - if (mmap_write_lock_killable(oldmm)) - return -EINTR; + mmap_assert_write_locked(oldmm); flush_cache_dup_mm(oldmm); uprobe_dup_mmap(oldmm, mm); /* @@ -653,11 +652,6 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, /* No ordering required: file already has been exposed. */ dup_mm_exe_file(mm, oldmm); - mm->total_vm = oldmm->total_vm; - mm->data_vm = oldmm->data_vm; - mm->exec_vm = oldmm->exec_vm; - mm->stack_vm = oldmm->stack_vm; - /* Use __mt_dup() to efficiently build an identical maple tree. */ retval = __mt_dup(&oldmm->mm_mt, &mm->mm_mt, GFP_KERNEL); if (unlikely(retval)) @@ -824,7 +818,7 @@ static inline void mm_free_pgd(struct mm_struct *mm) #else static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm) { - mmap_write_lock(oldmm); + mmap_assert_write_locked(oldmm); dup_mm_exe_file(mm, oldmm); mmap_write_unlock(oldmm); return 0; @@ -1705,12 +1699,19 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, if (!mm) goto fail_nomem; + uprobe_start_dup_mmap(); + if (mmap_write_lock_killable(oldmm)) { + free_mm(mm); + goto fail_uprobe; + } + memcpy(mm, oldmm, sizeof(*mm)); - if (!mm_init(mm, tsk, mm->user_ns)) - goto fail_nomem; + if (!mm_init(mm, tsk, mm->user_ns)) { + mmap_write_unlock(oldmm); + goto fail_uprobe; + } - uprobe_start_dup_mmap(); err = dup_mmap(mm, oldmm); if (err) goto free_pt; @@ -1729,9 +1730,10 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, mm->binfmt = NULL; mm_init_owner(mm, NULL); mmput(mm); - if (err) - uprobe_end_dup_mmap(); - + if (!err) + return NULL; +fail_uprobe: + uprobe_end_dup_mmap(); fail_nomem: return NULL; } -- 2.53.0