On 07/15/14 10:12, Joonsoo Kim wrote: > On Wed, Jul 09, 2014 at 03:30:14PM +0400, Andrey Ryabinin wrote: >> We need to manually unpoison rounded up allocation size for dname >> to avoid kasan's reports in __d_lookup_rcu. >> __d_lookup_rcu may validly read a little beyound allocated size. > > If it read a little beyond allocated size, IMHO, it is better to > allocate correct size. > > kmalloc(name->len + 1, GFP_KERNEL); --> > kmalloc(roundup(name->len + 1, sizeof(unsigned long ), GFP_KERNEL); > > Isn't it? > It's not needed here because kmalloc always roundup allocation size. This out of bound access happens in dentry_string_cmp() if CONFIG_DCACHE_WORD_ACCESS=y. dentry_string_cmp() relays on fact that kmalloc always round up allocation size, in other words it's by design. That was discussed some time ago here - https://lkml.org/lkml/2013/10/3/493. Since filesystem's maintainer don't want to add needless round up here, I'm not going to do it. I think this patch needs only more detailed description why we not simply allocate more. Also I think it would be better to rename unpoisoin_shadow to something like kasan_mark_allocated(). > Thanks. > >> >> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> >> Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> >> --- >> fs/dcache.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/fs/dcache.c b/fs/dcache.c >> index b7e8b20..dff64f2 100644 >> --- a/fs/dcache.c >> +++ b/fs/dcache.c >> @@ -38,6 +38,7 @@ >> #include <linux/prefetch.h> >> #include <linux/ratelimit.h> >> #include <linux/list_lru.h> >> +#include <linux/kasan.h> >> #include "internal.h" >> #include "mount.h" >> >> @@ -1412,6 +1413,8 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name) >> kmem_cache_free(dentry_cache, dentry); >> return NULL; >> } >> + unpoison_shadow(dname, >> + roundup(name->len + 1, sizeof(unsigned long))); >> } else { >> dname = dentry->d_iname; >> } >> -- >> 1.8.5.5 >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@xxxxxxxxx. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
