From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EFDFB423782; Thu, 30 Jul 2026 15:44:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785426265; cv=none; b=stEtwAIs576+OCeU77LgawfiDp9RGS7JpY/f98+IkbXBUuMirijCRr0pLbvE/zxB6l7vzkt2BGt7jmouGefEDy1k9G+/UqW8/AbZYL8jV+aueD8xL8SQDA0ZCONS8OnX0QwPC7Dy5xgqPLqiAXsXcwBIzllW5bt7KWTiX55N2v4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785426265; c=relaxed/simple; bh=LzxnDD/nD/acNX/qOCOteCpo7BuIeZiSLDPDWfWFrt8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nKZvalFhRgI/ETcZO7SwtzOoLx6Uh2STKQwnKZqh1Q7ASAHtS7RoFuARPGV01uaU0S4Il+UauWITygGfLpCGLVVl4dkmP0BJceLg6WINz9YrW4ugpOKdhSYqERSnUXFvskX8lUD7Z6LPkvxeCDKJ4Opq/lDxK0bYkJjYposYo+M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=DnEaaSY7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="DnEaaSY7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 561621F000E9; Thu, 30 Jul 2026 15:44:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1785426263; bh=MNh/8eYroXVgG9D6HhEw5K+SULncdPP+q0GK8yPKOBE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=DnEaaSY7E1mNrsNdUxfssBfvfaUjoOFg7y9OMsb9SjHFAUXlt1RXEbqiFdG1fi+0q Pb00CRakaIXNWZMZBlk30SE6V1OTsdKgDls/OOmtFpMy3vXhDb2DVg/N5Rm3r1Q4tM OuAOG+aJzFjWE+LLCKBOqlKxHqTEZXzTxLr087No= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "David Hildenbrand (Arm)" , "Christian Brauner (Amutable)" Subject: [PATCH 6.12 357/602] exec: fix unsigned loop counter wrap in transfer_args_to_stack() Date: Thu, 30 Jul 2026 16:12:29 +0200 Message-ID: <20260730141443.463707190@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260730141435.976815864@linuxfoundation.org> References: <20260730141435.976815864@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner commit 16cc4f5c1c4b9e45eca7f7deefa5410a292db599 upstream. The stop value is derived from bprm->p >> PAGE_SHIFT. The index variable is an unsigned long. If bprm->p drops below PAGE_SIZE and stop becomes zero the loop condition index >= stop is always true. After the index == 0 iteration the decrement wraps to ULONG_MAX and bprm->page[ULONG_MAX] reads sizeof(void *) bytes in front of the array. The pointer has wrapped to -1. That garbage pointer is then passed to kmap_local_page() and PAGE_SIZE bytes are copied from wherever that lands into the stack of the process being created. And the loop doesn't terminate either... Getting there only requires bprm->p < PAGE_SIZE. On !MMU bprm_set_stack_limit() and bprm_hit_stack_limit() are empty. So the only constraint on how far bprm->p is pushed down is valid_arg_len(), i.e. that each individual string still fits in what is left. bprm->p starts at PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *) so a single argument or environment string of a little over 31 pages leaves it in the first page: Oops - load access fault [#1] CPU: 0 UID: 0 PID: 1 Comm: victim Not tainted 7.2.0-rc4 #1 epc : __memcpy+0xd4/0xf8 ra : transfer_args_to_stack+0xaa/0xae s4 : ffffffffffffffff s2 : 0000000000000000 a1 : ffffffdc98000000 a2 : 0000000000001000 status: 0000000a00001880 badaddr: ffffffdc98000000 cause: 0000000000000005 [<801a5324>] __memcpy+0xd4/0xf8 [<800d5f6a>] load_flat_binary+0x43a/0x65e [<800a2de4>] bprm_execve+0x1d4/0x316 [<800a351a>] do_execveat_common+0x12e/0x138 [<800a3d44>] __riscv_sys_execve+0x38/0x4e Kernel panic - not syncing: Fatal exception in interrupt This is an arcane bug but we should still fix it. Count down from MAX_ARG_PAGES so the loop ends when index reaches stop, stop == 0 included. The iterations performed are unchanged for every other value of stop. Only CONFIG_MMU=n builds are affected, transfer_args_to_stack() is used by binfmt_flat and binfmt_elf_fdpic on nommu only. The loop predates git history. commit 7e7ec6a93434 ("elf_fdpic_transfer_args_to_stack(): make it generic") only moved it from binfmt_elf_fdpic.c into fs/exec.c and narrowed the copy to the used part of the first page. The condition and the decrement are unchanged from 2.6.12-rc2. Link: https://patch.msgid.link/20260721-hochachtung-staumauer-pigmente-15d71f7d7d04@brauner Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Reviewed-by: David Hildenbrand (Arm) Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/exec.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/exec.c +++ b/fs/exec.c @@ -856,7 +856,7 @@ int transfer_args_to_stack(struct linux_ stop = bprm->p >> PAGE_SHIFT; sp = *sp_location; - for (index = MAX_ARG_PAGES - 1; index >= stop; index--) { + for (index = MAX_ARG_PAGES; index-- > stop; ) { unsigned int offset = index == stop ? bprm->p & ~PAGE_MASK : 0; char *src = kmap_local_page(bprm->page[index]) + offset; sp -= PAGE_SIZE - offset;