Zhu Yanjun <zyjzyj2...@gmail.com> writes: > On Wed, Dec 9, 2020 at 1:12 AM Daniel Borkmann <dan...@iogearbox.net> wrote: >> >> On 12/9/20 6:03 AM, Zhu Yanjun wrote: >> > In the function xdp_umem_pin_pages, if npgs != umem->npgs and >> > npgs >= 0, the function xdp_umem_unpin_pages is called. In this >> > function, kfree is called to handle umem->pgs, and then in the >> > function xdp_umem_pin_pages, kfree is called again to handle >> > umem->pgs. Eventually, umem->pgs is freed twice. >> > >> > Acked-by: Björn Töpel <bjorn.to...@intel.com> >> > Signed-off-by: Zhu Yanjun <yanjun....@intel.com> >> >> Please also fix up the commit log according to Bjorn's prior feedback [0]. >> If it's just a cleanup, it should state so, the commit message right now >> makes it sound like an actual double free bug. > > The umem->pgs is actually freed twice. Since umem->pgs is set to NULL > after the first kfree, > the second kfree would not trigger call trace. > IMO, the commit log is very clear about this.
Yes, it is very clear; and also wrong. As someone already pointed out, passing a NULL pointer to kfree() doesn't actually lead to a double free: https://elixir.bootlin.com/linux/latest/source/mm/slub.c#L4106 -Toke
