Re: bpf: use-after-free in array_map_alloc

[Tejun Heo]

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.

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);
+
        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);
+
        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);
+
                pcpu_for_each_pop_region(chunk, rs, re, 0, pcpu_unit_pages) {
                        pcpu_depopulate_chunk(chunk, rs, re);
                        spin_lock_irq(&pcpu_lock);