Nice catch. A nicer fix will be to check the type of the header, and copy the header accordingly. Attached is a patch following this idea.
On Oct 18, 2012, at 03:06 , "Kawashima, Takahiro" <t-kawashima_at_[hidden]> wrote:
> Hi Open MPI developers,
> I found another issue in Open MPI.
> In MCA_PML_OB1_RECV_FRAG_INIT macro in ompi/mca/pml/ob1/pml_ob1_recvfrag.h
> file, we copy a PML header from an arrived message to another buffer,
> as follows:
> frag->hdr = *(mca_pml_ob1_hdr_t*)hdr;
> On this copy, we cast hdr to mca_pml_ob1_hdr_t, which is a union
> of all actual header structs such as mca_pml_ob1_match_hdr_t.
> This means we copy the buffer of the size of the largest header
> even if the arrived message is smaller than it. This can cause
> SEGV if the arrived message is small and it is laid on the bottom
> of the page. Actually, my tofu BTL, the BTL component of Fujitsu
> MPI for K computer, suffered from this.
> The attached patch will be one of possible fixes for this issue.
> This fix assume that the arrived header has at least segs.seg_len
> bytes. This is always true for current Open MPI code because hdr
> equals to segs.seg_addr.pval. There may exist a smarter fix.
> Takahiro Kawashima,
> MPI development team,
> devel mailing list