Messages in this thread | | | Subject | Re: [PATCH] cxgb4: fix undefined behavior in mem.c | From | Bart Van Assche <> | Date | Thu, 28 Feb 2019 14:56:36 -0800 |
| |
On Thu, 2019-02-28 at 15:38 -0700, Shaobo He wrote: > In function `c4iw_dealloc_mw`, variable mhp's value is printed after > freed, which triggers undefined behavior according to this post: > https://trust-in-soft.com/dangling-pointer-indeterminate/. > > This commit fixes it by swapping the order of `kfree` and `pr_debug`. > > Signed-off-by: Shaobo He <shaobo@cs.utah.edu> > --- > drivers/infiniband/hw/cxgb4/mem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/infiniband/hw/cxgb4/mem.c b/drivers/infiniband/hw/cxgb4/mem.c > index 7b76e6f..bb8e0bc 100644 > --- a/drivers/infiniband/hw/cxgb4/mem.c > +++ b/drivers/infiniband/hw/cxgb4/mem.c > @@ -684,8 +684,8 @@ int c4iw_dealloc_mw(struct ib_mw *mw) > mhp->wr_waitp); > kfree_skb(mhp->dereg_skb); > c4iw_put_wr_wait(mhp->wr_waitp); > - kfree(mhp); > pr_debug("ib_mw %p mmid 0x%x ptr %p\n", mw, mmid, mhp); > + kfree(mhp); > return 0; > }
Please quote the relevant paragraphs from the C standard. All I have found about free() in ISO/IEC 9899:2017 is the following:
Description The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined.
That is not sufficient to claim that the above code triggers undefined behavior.
Bart.
| |