On Wed 01-08-18 15:04:18, Jeremy Linton wrote: > Its possible to crash __alloc_pages_nodemask by passing it > bogus node ids. This is caused by NODE_DATA() returning null > (hopefully) when the requested node is offline. We can > harded against the basic case of a mostly valid node, that > isn't online by checking for null and failing prepare_alloc_pages. > > But this then suggests we should also harden NODE_DATA() like this > > #define NODE_DATA(nid) ( (nid) < MAX_NUMNODES ? node_data[(nid)] : NULL) > > eventually this starts to add a bunch of generally uneeded checks > in some code paths that are called quite frequently. But the page allocator is really a hot path and people will not be happy to have yet another branch there. No code should really use invalid numa node ids in the first place. If I remember those bugs correctly then it was the arch code which was doing something wrong. I would prefer that code to be fixed instead. > Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx> > --- > include/linux/gfp.h | 2 ++ > mm/page_alloc.c | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index a6afcec53795..17d70271c42e 100644 > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -436,6 +436,8 @@ static inline int gfp_zonelist(gfp_t flags) > */ > static inline struct zonelist *node_zonelist(int nid, gfp_t flags) > { > + if (unlikely(!NODE_DATA(nid))) //VM_WARN_ON? > + return NULL; > return NODE_DATA(nid)->node_zonelists + gfp_zonelist(flags); > } > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a790ef4be74e..3a3d9ac2662a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4306,6 +4306,8 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order, > { > ac->high_zoneidx = gfp_zone(gfp_mask); > ac->zonelist = node_zonelist(preferred_nid, gfp_mask); > + if (!ac->zonelist) > + return false; > ac->nodemask = nodemask; > ac->migratetype = gfpflags_to_migratetype(gfp_mask); > > -- > 2.14.3 > -- Michal Hocko SUSE Labs