From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx201.postini.com [74.125.245.201]) by kanga.kvack.org (Postfix) with SMTP id ED55E6B0036 for ; Tue, 12 Mar 2013 00:23:27 -0400 (EDT) Received: by mail-ob0-f176.google.com with SMTP id v19so4007321obq.7 for ; Mon, 11 Mar 2013 21:23:27 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20130312002429.GA24360@google.com> References: <1356050997-2688-1-git-send-email-walken@google.com> <1356050997-2688-5-git-send-email-walken@google.com> <20130311160322.830cc6b670fd24faa8366413@linux-foundation.org> <20130312002429.GA24360@google.com> Date: Tue, 12 Mar 2013 12:23:26 +0800 Message-ID: Subject: Re: [PATCH 4/9] mm: use mm_populate() for blocking remap_file_pages() From: Hillf Danton Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Michel Lespinasse Cc: Andrew Morton , Tommi Rantala , Andy Lutomirski , Ingo Molnar , Al Viro , Hugh Dickins , Jorn_Engel , Rik van Riel , Linux-MM , LKML On Tue, Mar 12, 2013 at 8:24 AM, Michel Lespinasse wrote: > (Sorry for the late reply) > > On Mon, Mar 11, 2013 at 4:03 PM, Andrew Morton wrote: >> On Sun, 10 Mar 2013 20:55:21 +0200 Tommi Rantala wrote: >> >>> 2012/12/21 Michel Lespinasse : >>> > Signed-off-by: Michel Lespinasse >>> >>> Hello, this patch introduced the following bug, seen while fuzzing with trinity: >>> >>> [ 396.825414] BUG: unable to handle kernel NULL pointer dereference >>> at 0000000000000050 > > Good catch... > >> From: Andrew Morton >> Subject: mm/fremap.c: fix oops on error path >> >> If find_vma() fails, sys_remap_file_pages() will dereference `vma', which >> contains NULL. Fix it by checking the pointer. >> >> (We could alternatively check for err==0, but this seems more direct) >> >> (The vm_flags change is to squish a bogus used-uninitialised warning >> without adding extra code). >> >> Reported-by: Tommi Rantala >> Cc: Michel Lespinasse >> Signed-off-by: Andrew Morton >> --- >> >> mm/fremap.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff -puN mm/fremap.c~mm-fremapc-fix-oops-on-error-path mm/fremap.c >> --- a/mm/fremap.c~mm-fremapc-fix-oops-on-error-path >> +++ a/mm/fremap.c >> @@ -163,7 +163,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsign >> * and that the remapped range is valid and fully within >> * the single existing vma. >> */ >> - if (!vma || !(vma->vm_flags & VM_SHARED)) >> + vm_flags = vma->vm_flags; >> + if (!vma || !(vm_flags & VM_SHARED)) >> goto out; > > Your commit message indicates the vm_flags load here doesn't generate any code, but this seems very brittle and compiler dependent. If the compiler was to generate an actual load here, the issue with vma == NULL would reappear. > >> if (!vma->vm_ops || !vma->vm_ops->remap_pages) >> @@ -254,7 +255,8 @@ get_write_lock: >> */ >> >> out: >> - vm_flags = vma->vm_flags; >> + if (vma) >> + vm_flags = vma->vm_flags; >> if (likely(!has_write_lock)) >> up_read(&mm->mmap_sem); >> else > > > > Would the following work ? I think it's simpler, and with the compiler > I'm using here it doesn't emit warnings: > > diff --git a/mm/fremap.c b/mm/fremap.c > index 0cd4c11488ed..329507e832fb 100644 > --- a/mm/fremap.c > +++ b/mm/fremap.c > @@ -254,7 +254,8 @@ get_write_lock: > */ > > out: > - vm_flags = vma->vm_flags; > + if (!err) > + vm_flags = vma->vm_flags; > if (likely(!has_write_lock)) > up_read(&mm->mmap_sem); > else > Is it still necessary to populate mm if bail out due to a linear mapping encountered? Hillf -- 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/ . Don't email: email@kvack.org