[+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);
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