On Tue, Mar 12, 2013 at 8:24 AM, Michel Lespinasse <walken@xxxxxxxxxx> wrote: > (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 > 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@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>