| Message ID | 20211023171802.4693-1-cyeaa@connect.ust.hk (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/kfence: fix null pointer dereference on pointer meta | expand |
On Sat, 23 Oct 2021 at 19:20, Chengfeng Ye <cyeaa@connect.ust.hk> wrote: > The pointer meta return from addr_to_metadata could be null, so > there is a potential null pointer dereference issue. Fix this > by adding a null check before dereference. > > Fixes: 0ce20dd8 ("mm: add Kernel Electric-Fence infrastructure") > Signed-off-by: Chengfeng Ye <cyeaa@connect.ust.hk> > --- > mm/kfence/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/kfence/core.c b/mm/kfence/core.c > index 7a97db8bc8e7..7d2ec787e921 100644 > --- a/mm/kfence/core.c > +++ b/mm/kfence/core.c > @@ -811,7 +811,7 @@ void __kfence_free(void *addr) > * objects once it has been freed. meta->cache may be NULL if the cache > * was destroyed. > */ > - if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) > + if (unlikely(meta && meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) > call_rcu(&meta->rcu_head, rcu_guarded_free); > else > kfence_guarded_free(addr, meta, false); Sorry -- Nack. What bug did you encounter? Please see [1], and I'm afraid this attempt makes even less sense because if it were (hypothetically) NULL like you say we just call kfence_guarded_free() and crash there. [1] https://lkml.kernel.org/r/CANpmjNMcgUsdvXrvQHn+-y1w-z-6QAS+WJ27RB2DCnVxORRcuw@mail.gmail.com However, what I wrote in [1] equally applies here: > [...] > Adding a check like this could also hide genuine bugs, as meta should > never be NULL in __kfence_free(). If it is, we'd like to see a crash. > > Did you read kfence_free() in include/linux/kfence.h? It already > prevents __kfence_free() being called with a non-KFENCE address. > > Without a more thorough explanation, Nack. May I ask which static analysis tool keeps flagging this? Thanks, -- Marco
diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 7a97db8bc8e7..7d2ec787e921 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -811,7 +811,7 @@ void __kfence_free(void *addr) * objects once it has been freed. meta->cache may be NULL if the cache * was destroyed. */ - if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) + if (unlikely(meta && meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) call_rcu(&meta->rcu_head, rcu_guarded_free); else kfence_guarded_free(addr, meta, false);
The pointer meta return from addr_to_metadata could be null, so there is a potential null pointer dereference issue. Fix this by adding a null check before dereference. Fixes: 0ce20dd8 ("mm: add Kernel Electric-Fence infrastructure") Signed-off-by: Chengfeng Ye <cyeaa@connect.ust.hk> --- mm/kfence/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)