From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx204.postini.com [74.125.245.204]) by kanga.kvack.org (Postfix) with SMTP id 284566B0044 for ; Mon, 2 Apr 2012 13:14:51 -0400 (EDT) Received: by bkwq16 with SMTP id q16so3234644bkw.14 for ; Mon, 02 Apr 2012 10:14:49 -0700 (PDT) Message-ID: <4F79DE84.8020807@openvz.org> Date: Mon, 02 Apr 2012 21:14:44 +0400 From: Konstantin Khlebnikov MIME-Version: 1.0 Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE References: <20120331091049.19373.28994.stgit@zurg> <20120331092929.19920.54540.stgit@zurg> <20120331201324.GA17565@redhat.com> <20120331203912.GB687@moon> <4F79755B.3030703@openvz.org> <20120402144821.GA3334@redhat.com> <4F79D1AF.7080100@openvz.org> <20120402162733.GI7607@moon> In-Reply-To: <20120402162733.GI7607@moon> Content-Type: multipart/mixed; boundary="------------020001050501020607050609" Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: Oleg Nesterov , "linux-mm@kvack.org" , Andrew Morton , "linux-kernel@vger.kernel.org" , Eric Paris This is a multi-part message in MIME format. --------------020001050501020607050609 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cyrill Gorcunov wrote: > On Mon, Apr 02, 2012 at 08:19:59PM +0400, Konstantin Khlebnikov wrote: >> Oleg Nesterov wrote: >>> On 04/02, Konstantin Khlebnikov wrote: >>>> >>>> In this patch I leave mm->exe_file lockless. >>>> After exec/fork we can change it only for current task and only if mm->mm_users == 1. >>>> >>>> something like this: >>>> >>>> task_lock(current); >>> >>> OK, this protects against the race with get_task_mm() >>> >>>> if (atomic_read(¤t->mm->mm_users) == 1) >>> >>> this means PR_SET_MM_EXE_FILE can fail simply because someone did >>> get_task_mm(). Or the caller is multithreaded. >> >> This is sad, seems like we should keep mm->exe_file protection by mm->mmap_sem. >> So, I'll rework this patch... > > Ah, it's about locking. I misundertand it at first. > Oleg, forget about my email then. Yes, it's about locking. Please review patch for your code from attachment. --------------020001050501020607050609 Content-Type: text/plain; name="diff-pr-set-mm-exe-file-without-vm_executable" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="diff-pr-set-mm-exe-file-without-vm_executable" diff --git a/include/linux/sched.h b/include/linux/sched.h index cff94cd..4a41270 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -437,6 +437,7 @@ extern int get_dumpable(struct mm_struct *mm); /* leave room for more dump flags */ #define MMF_VM_MERGEABLE 16 /* KSM may merge identical pages */ #define MMF_VM_HUGEPAGE 17 /* set when VM_HUGEPAGE is set on vma */ +#define MMF_EXE_FILE_CHANGED 18 /* see prctl(PR_SET_MM_EXE_FILE) */ #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK) diff --git a/kernel/sys.c b/kernel/sys.c index da660f3..b217069 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1714,17 +1714,11 @@ static bool vma_flags_mismatch(struct vm_area_struct *vma, static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) { + struct vm_area_struct *vma; struct file *exe_file; struct dentry *dentry; int err; - /* - * Setting new mm::exe_file is only allowed when no VM_EXECUTABLE vma's - * remain. So perform a quick test first. - */ - if (mm->num_exe_file_vmas) - return -EBUSY; - exe_file = fget(fd); if (!exe_file) return -EBADF; @@ -1745,17 +1739,28 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) if (err) goto exit; + down_write(&mm->mmap_sem); + /* + * Forbid mm->exe_file change if there are mapped some other files. + */ + err = -EEXIST; + for (vma = mm->mmap; vma; vma = vma->vm_next) { + if (vma->vm_file && + !path_equal(&vma->vm_file->f_path, &exe_file->f_path)) + goto out_unlock; + } /* * The symlink can be changed only once, just to disallow arbitrary * transitions malicious software might bring in. This means one * could make a snapshot over all processes running and monitor * /proc/pid/exe changes to notice unusual activity if needed. */ - down_write(&mm->mmap_sem); - if (likely(!mm->exe_file)) - set_mm_exe_file(mm, exe_file); - else - err = -EBUSY; + err = -EBUSY; + if (test_and_set_bit(MMF_EXE_FILE_CHANGED, &mm->flags)) + goto out_unlock; + set_mm_exe_file(mm, exe_file); + err = 0; +out_unlock: up_write(&mm->mmap_sem); exit: --------------020001050501020607050609-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org