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Message-ID: <57441396.2050607@suse.cz> Date: Tue, 24 May 2016 10:40:54 +0200 From: Vlastimil Babka <vbabka@...e.cz> To: Tejun Heo <tj@...nel.org> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Sasha Levin <sasha.levin@...cle.com>, ast@...nel.org, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Christoph Lameter <cl@...ux.com>, Linux-MM layout <linux-mm@...ck.org>, marco.gra@...il.com Subject: Re: bpf: use-after-free in array_map_alloc [+CC Marco who reported the CVE, forgot that earlier] On 05/23/2016 11:35 PM, Tejun Heo wrote: > Hello, > > Can you please test whether this patch resolves the issue? While > adding support for atomic allocations, I reduced alloc_mutex covered > region too much. > > Thanks. Ugh, this makes the code even more head-spinning than it was. > diff --git a/mm/percpu.c b/mm/percpu.c > index 0c59684..bd2df70 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -162,7 +162,7 @@ static struct pcpu_chunk *pcpu_reserved_chunk; > static int pcpu_reserved_chunk_limit; > > static DEFINE_SPINLOCK(pcpu_lock); /* all internal data structures */ > -static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop */ > +static DEFINE_MUTEX(pcpu_alloc_mutex); /* chunk create/destroy, [de]pop, map extension */ > > static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */ > > @@ -435,6 +435,8 @@ static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc) > size_t old_size = 0, new_size = new_alloc * sizeof(new[0]); > unsigned long flags; > > + lockdep_assert_held(&pcpu_alloc_mutex); I don't see where the mutex gets locked when called via pcpu_map_extend_workfn? (except via the new cancel_work_sync() call below?) Also what protects chunks with scheduled work items from being removed? > + > new = pcpu_mem_zalloc(new_size); > if (!new) > return -ENOMEM; > @@ -895,6 +897,9 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > return NULL; > } > > + if (!is_atomic) > + mutex_lock(&pcpu_alloc_mutex); BTW I noticed that bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL; this is too pessimistic IMHO. Reclaim is possible even without __GFP_FS and __GFP_IO. Could you just use gfpflags_allow_blocking(gfp) here? > + > spin_lock_irqsave(&pcpu_lock, flags); > > /* serve reserved allocations from the reserved chunk if available */ > @@ -967,12 +972,11 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > if (is_atomic) > goto fail; > > - mutex_lock(&pcpu_alloc_mutex); > + lockdep_assert_held(&pcpu_alloc_mutex); > > if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) { > chunk = pcpu_create_chunk(); > if (!chunk) { > - mutex_unlock(&pcpu_alloc_mutex); > err = "failed to allocate new chunk"; > goto fail; > } > @@ -983,7 +987,6 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > spin_lock_irqsave(&pcpu_lock, flags); > } > > - mutex_unlock(&pcpu_alloc_mutex); > goto restart; > > area_found: > @@ -993,8 +996,6 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > if (!is_atomic) { > int page_start, page_end, rs, re; > > - mutex_lock(&pcpu_alloc_mutex); > - > page_start = PFN_DOWN(off); > page_end = PFN_UP(off + size); > > @@ -1005,7 +1006,6 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > > spin_lock_irqsave(&pcpu_lock, flags); > if (ret) { > - mutex_unlock(&pcpu_alloc_mutex); > pcpu_free_area(chunk, off, &occ_pages); > err = "failed to populate"; > goto fail_unlock; > @@ -1045,6 +1045,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, > /* see the flag handling in pcpu_blance_workfn() */ > pcpu_atomic_alloc_failed = true; > pcpu_schedule_balance_work(); > + } else { > + mutex_unlock(&pcpu_alloc_mutex); > } > return NULL; > } > @@ -1137,6 +1139,8 @@ static void pcpu_balance_workfn(struct work_struct *work) > list_for_each_entry_safe(chunk, next, &to_free, list) { > int rs, re; > > + cancel_work_sync(&chunk->map_extend_work); This deserves some comment? > + > pcpu_for_each_pop_region(chunk, rs, re, 0, pcpu_unit_pages) { > pcpu_depopulate_chunk(chunk, rs, re); > spin_lock_irq(&pcpu_lock); > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@...ck.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a> >
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