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=1794634464; b=D3eSNiY2YtSq41aLIx1LttrKBQ0pK363df9gi4UGAUWYPsEoT6N0OjMdk/K6Qyj1/pXz bAxpkV5lg3M5MT5caZyfJCgpaPFL3TgUnfIWrTvup2GUfWDnIrD8B7u/yz9p1rsDiDuF+ IADjuSLwgT8cDZzaawTFjuDwHXn45do1uc14FRSYziPupu0tq3l+cRZxm1/wk0lORB5rq uBB5ApL+OPyLiWZIcs+mHsC4p7H3kdrFoyWuNghKYM2PyZrJTyuSOt/jGSllLfKsPn/hw BEM9jTYYakpWRPGeYg0daSZYv2WFyKM5xNs25YO1sGpyBuzej1XX50m1rdFepBSlV1A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794634464; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=zPvbwgVC0WA/qfAih4aLx67Xfb+m0t2N5WaKKKP19ig=; b=MTwSTRzRP2xkvMRJMWt63GXNdfqDVte0owoEjYMTKzYIraga1kgy6fUwqqa+TB2Cboqq N/9Q7OkLnvpneCFD5SmZrpeO3yK59W8v8ZH2MEUiKAqQu1N7X76TC4Hzpm7t4DyHTcSPV b1yDyaCi58X7w13jmSDbJynmN5Mce3KWNaYnYgq2Wa6bHzOl80KvpD0+6cGL+/Nrvsr8J 9RB6lXyrZI/gd3kTrIKcQY/uFDNqj6mIHxDOSZWVVbpvQo5nz315MiXY+mpI1lpGgvBuE DxKVXnQwA+RkTnZTgbRkX6OcV1bB0mrDE3ZNX352XjB8+XoRvPTyoUWAM+fDDaiNWEg== 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=c5mFvHTX; 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 B9981606A327 for ; Sat, 14 Nov 2026 05:34:24 +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=c5mFvHTX Received: by smtp.kernel.org (Postfix) with ESMTPSA id 490DC1F000C4; Sat, 14 Nov 2026 05:34:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794634464; bh=zPvbwgVC0WA/qfAih4aLx67Xfb+m0t2N5WaKKKP19ig=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=c5mFvHTXf4wJizR7XCZQlotjwhjzHeraWuwY5SZayMTOOBj7rqpx1m5MGGpTw3hrg 9R+5v5a/0Hw4aBb9IqzoWR7yHn9OoWZ9PMSsJTPzJyZ/0AkT0/rXEyfdHeijzOYz6t q03NUzGxm2tTdtQ/TeA6VnR1shkfSwpmqN2DZotY/rZkgzDKETQgfFF/moIVRJZLtK R9EfQ6TSZqghVfM72jlTb8SBZk0pH5zXh+HjCeWXe4R3k9rl+ULs0KqDRGtlSW5Uly hUlYIOgZ21AB9LRrMQqm18TGyG2t2nm1wdKGaMaTIA9LxG1xqNVLn+8R6bXJUv0BXC z3t0//MI+FGRQ== 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 6.6.y] fork: take mmap_lock before copying mm_struct Date: Sat, 14 Nov 2026 00:34:22 -0500 Message-ID: <20261114053403.3113729-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109201122-failed-6.6-ef694e2d2101@kernel.org> References: <20261109201122-failed-6.6-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: Adjusted failure handling because dup_mmap() already performs uprobe cleanup, avoiding a double unlock. ] Signed-off-by: Sasha Levin --- kernel/fork.c | 29 +++++++++++++++-------------- 1 file changed, 15 insertions(+), 14 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index fd10c6e0dcfa3..625f9bd101dbb 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -655,11 +655,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, VMA_ITERATOR(old_vmi, oldmm, 0); VMA_ITERATOR(vmi, mm, 0); - uprobe_start_dup_mmap(); - if (mmap_write_lock_killable(oldmm)) { - retval = -EINTR; - goto fail_uprobe_end; - } + mmap_assert_write_locked(oldmm); flush_cache_dup_mm(oldmm); uprobe_dup_mmap(oldmm, mm); /* @@ -670,11 +666,6 @@ 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; - retval = ksm_fork(mm, oldmm); if (retval) goto out; @@ -782,7 +773,6 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, flush_tlb_mm(oldmm); mmap_write_unlock(oldmm); dup_userfaultfd_complete(&uf); -fail_uprobe_end: uprobe_end_dup_mmap(); return retval; @@ -813,7 +803,7 @@ 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; @@ -1695,10 +1685,18 @@ 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; + } err = dup_mmap(mm, oldmm); if (err) @@ -1717,7 +1715,10 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, mm->binfmt = NULL; mm_init_owner(mm, NULL); mmput(mm); + return NULL; +fail_uprobe: + uprobe_end_dup_mmap(); fail_nomem: return NULL; } -- 2.53.0