page_pool: Fix use-after-free in page_pool_recycle_in_ring

syzbot reported a uaf in page_pool_recycle_in_ring:

BUG: KASAN: slab-use-after-free in lock_release+0x151/0xa30 kernel/locking/lockdep.c:5862
Read of size 8 at addr ffff8880286045a0 by task syz.0.284/6943

CPU: 0 UID: 0 PID: 6943 Comm: syz.0.284 Not tainted 6.13.0-rc3-syzkaller-gdfa94ce54f41 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x169/0x550 mm/kasan/report.c:489
kasan_report+0x143/0x180 mm/kasan/report.c:602
lock_release+0x151/0xa30 kernel/locking/lockdep.c:5862
__raw_spin_unlock_bh include/linux/spinlock_api_smp.h:165 [inline]
_raw_spin_unlock_bh+0x1b/0x40 kernel/locking/spinlock.c:210
spin_unlock_bh include/linux/spinlock.h:396 [inline]
ptr_ring_produce_bh include/linux/ptr_ring.h:164 [inline]
page_pool_recycle_in_ring net/core/page_pool.c:707 [inline]
page_pool_put_unrefed_netmem+0x748/0xb00 net/core/page_pool.c:826
page_pool_put_netmem include/net/page_pool/helpers.h:323 [inline]
page_pool_put_full_netmem include/net/page_pool/helpers.h:353 [inline]
napi_pp_put_page+0x149/0x2b0 net/core/skbuff.c:1036
skb_pp_recycle net/core/skbuff.c:1047 [inline]
skb_free_head net/core/skbuff.c:1094 [inline]
skb_release_data+0x6c4/0x8a0 net/core/skbuff.c:1125
skb_release_all net/core/skbuff.c:1190 [inline]
__kfree_skb net/core/skbuff.c:1204 [inline]
sk_skb_reason_drop+0x1c9/0x380 net/core/skbuff.c:1242
kfree_skb_reason include/linux/skbuff.h:1263 [inline]
__skb_queue_purge_reason include/linux/skbuff.h:3343 [inline]

root cause is:

page_pool_recycle_in_ring
ptr_ring_produce
spin_lock(&r->producer_lock);
WRITE_ONCE(r->queue[r->producer++], ptr)
//recycle last page to pool
page_pool_release
page_pool_scrub
page_pool_empty_ring
ptr_ring_consume
page_pool_return_page //release all page
__page_pool_destroy
free_percpu(pool->recycle_stats);
free(pool) //free

spin_unlock(&r->producer_lock); //pool->ring uaf read
recycle_stat_inc(pool, ring);

page_pool can be free while page pool recycle the last page in ring.
Add producer-lock barrier to page_pool_release to prevent the page
pool from being free before all pages have been recycled.

recycle_stat_inc() is empty when CONFIG_PAGE_POOL_STATS is not
enabled, which will trigger Wempty-body build warning. Add definition
for pool stat macro to fix warning.

Suggested-by: Jakub Kicinski <[e-mail]>
Link: https://lore.kernel.org/netdev/[e-mail]
Fixes: ff7d6b27f894 ("page_pool: refurbish version of page_pool code")
Reported-by: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=204a4382fcb3311f3858
Signed-off-by: Dong Chenchen <[e-mail]>
Reviewed-by: Toke Høiland-Jørgensen <[e-mail]>
Reviewed-by: Mina Almasry <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/core/page_pool.c

···
 EXPORT_SYMBOL(page_pool_ethtool_stats_get);
 
 #else
-#define alloc_stat_inc(pool, __stat)
-#define recycle_stat_inc(pool, __stat)
-#define recycle_stat_add(pool, __stat, val)
+#define alloc_stat_inc(...)	do { } while (0)
+#define recycle_stat_inc(...)	do { } while (0)
+#define recycle_stat_add(...)	do { } while (0)
 #endif
 
 static bool page_pool_producer_lock(struct page_pool *pool)
···
 
 static bool page_pool_recycle_in_ring(struct page_pool *pool, netmem_ref netmem)
 {
-	int ret;
+	bool in_softirq, ret;
+
 	/* BH protection not needed if current is softirq */
-	if (in_softirq())
-		ret = ptr_ring_produce(&pool->ring, (__force void *)netmem);
-	else
-		ret = ptr_ring_produce_bh(&pool->ring, (__force void *)netmem);
-
-	if (!ret) {
+	in_softirq = page_pool_producer_lock(pool);
+	ret = !__ptr_ring_produce(&pool->ring, (__force void *)netmem);
+	if (ret)
 		recycle_stat_inc(pool, ring);
-		return true;
-	}
+	page_pool_producer_unlock(pool, in_softirq);
 
-	return false;
+	return ret;
 }
 
 /* Only allow direct recycling in special circumstances, into the
···
 
 static int page_pool_release(struct page_pool *pool)
 {
+	bool in_softirq;
 	int inflight;
 
 	page_pool_scrub(pool);
 	inflight = page_pool_inflight(pool, true);
+	/* Acquire producer lock to make sure producers have exited. */
+	in_softirq = page_pool_producer_lock(pool);
+	page_pool_producer_unlock(pool, in_softirq);
 	if (!inflight)
 		__page_pool_destroy(pool);