(Sorry for the late reply) On Mon, Mar 11, 2013 at 4:03 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 10 Mar 2013 20:55:21 +0200 Tommi Rantala <tt.rantala@xxxxxxxxx> wrote: > >> 2012/12/21 Michel Lespinasse <walken@xxxxxxxxxx>: >> > Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx> >> >> 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 <akpm@xxxxxxxxxxxxxxxxxxxx> > 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 <tt.rantala@xxxxxxxxx> > Cc: Michel Lespinasse <walken@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > 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 -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>