Thanks Ben for code review. I will leave explanation here for later reference.
When md2 context is a string of size 248, the headers's total length would be 256 bytes. Because there is only 6 bits in ver_flags_ttl_len for length value, the value of ver_flags_ttl_len is a wrong value of 0. In format_odp_push_nsh_action(), the first line of code is: size_t mdlen = nsh_hdr_len(nsh_hdr) - NSH_BASE_HDR_LEN; nsh_hdr_len(nsh_hdr) returns 0. As a result, mdlen will be a very large value. Later in this function, when mdlen is used as the upper limit to access md2_ctx, stack overflow will happen. On Fri, Oct 26, 2018 at 3:05 PM Ben Pfaff <[email protected]> wrote: > On Fri, Oct 26, 2018 at 02:55:55PM -0700, Ben Pfaff wrote: > > On Thu, Oct 25, 2018 at 02:41:50PM -0700, Yifeng Sun wrote: > > > In the filed of ver_flags_ttl_len of struct nshhdr, there are only 6 > > > bits that are used to indicate header's total length in 4-byte words. > > > Therefore, the max value for total is 252 (63x4), instead of 256 used > > > in present code base. This patch fixes it. > > > > > > Reported-at: > https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=10855 > > > Signed-off-by: Yifeng Sun <[email protected]> > > > > Thanks for the patch and the bug fix. > > > > Would you mind adding a few words to the commit message that explains > > how this can lead to stack overflow? > > Oops, I accidentally applied this anyway. Never mind on the commit > message update. > _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
