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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?xBr2WigME4FYc8QQsywInWkRVOXul+/biw+99RlSr8nmHMZek0ZkHdFsqjVU?= =?us-ascii?Q?rjaaHY/VRGUlAENCW6bRIfK5ufWdrnFrgeoHSQt9uur6l74zn7pm3fCtpA81?= =?us-ascii?Q?3rB75VXn7oM9dEIwxMv+42KJB22u113wJStoPDWW/05fzXJWpRk+jNftSQvj?= =?us-ascii?Q?fDlLQ6E40jpSl2gZy2qJEWkfNzVv6f+RhFnVvMjXRVweN/ix5jc9FwjWfeg/?= =?us-ascii?Q?OTGHFHkctHI+BmNhz+BYgFqLreWXq5QZtmKhNocu7v078qkB58nT/aY4yhu0?= =?us-ascii?Q?ptXOLe9BVghq7apdTcybYuLoL7595PTaHANv9gpLHK1C608x2OqAn5f4zpR9?= =?us-ascii?Q?bOwJdToruOKLGaTfqNo4utqEahTzFWH57BjfNKLs6qT3JKRabZYx0qIX1OY6?= =?us-ascii?Q?wVJoJTNSMg5Cq0K4cM20PBWOqq+27Hz/85L7HlA02EhCAi8fH6DOkfWbulUD?= =?us-ascii?Q?wfGmSFwPlGMvEBXmWk8vib0OsBv6ZUoMlU3sVlIQDzVUMTPf3BMHDc5nyJRu?= =?us-ascii?Q?aRibisHhavnsjEG/dpe+U+EjLfz6JsaDwufq1itluud+sxU7n89T9HhyHh/9?= =?us-ascii?Q?WTganuek25nJ/wuVFNufSoRiTqDvTZK4lYUJTInOGmtHbrYkvckAmn/J/D1U?= =?us-ascii?Q?/Zvl013tyqQtJOJ2n/MuyvTds49jAbrzTtkBDvhA4r7uXCBzU7q5VC+GuSUr?= =?us-ascii?Q?6llFsUaJYyy+skZyxYOhxu3y/xVyzM2fa3hLnifC183F1DMWN0HqY7r3WMBO?= =?us-ascii?Q?r8h966S5RwVbtxlhz+MmIfjq+gtYDe0/3hh6aWE1l36pXtwv1z7iUiGur5T1?= =?us-ascii?Q?YyemN80Cdun+TIWy7qhdY9h1832pyaUyKOfcUjeRzlO4CP1BP5JNndm6J9ht?= =?us-ascii?Q?MAwqePapkO4fniCVzcdqE/VnKJwwPVzyiP+yG7pdt6utC/6MGNM83orI1AP2?= =?us-ascii?Q?Njludbtlt2t+u7n589oUyPogum2W3PCmYbjf/y13Wy1JTa6eNcx0hBxGId8J?= =?us-ascii?Q?zSBppkIWQoSsvSV3LJYaOIb3qVLhGxYUBm8wizQd++kmbuXlzOxr3Jg6axsI?= =?us-ascii?Q?+4vwHd8BF0eGBjQbiTOHXyvQa020aXr/XVmRv/ZeDhYPHlwvKHg3MEOjDDPD?= =?us-ascii?Q?x556yi99z1jMN+y/wBHRlru5ocCK4RjcZx2zVaKi4ONgQsepYpnIwV2YJrZw?= =?us-ascii?Q?P0UvHecpOWYh1MtNOSE0+hpHw/f7MlkO9VLzi1wP9z+IvsAKeT6wvhcv+aTA?= =?us-ascii?Q?r9q99xqfhQMg8p6Wff+bx6/AIKmLzQcK3cQ8A+GnH3AcEPTR//O8X6UbX6p1?= =?us-ascii?Q?GLHBcKZD5+t4jXL0se9THsb9eJZ+/rMiOu3yxHmr3c79Ldvm7sSSHezaZzNP?= =?us-ascii?Q?J90gIvzJAv/M2RVfHCI+9VjRDGNGEx/d2oITKYBhhb75DSxT/UhO/Jzh3Ut7?= =?us-ascii?Q?IBiUsBU4LLL6aD5HDeLIN6Tw0PROL7j/MIFZuLZe5yeP9oCsei+CEBV2DsJ9?= =?us-ascii?Q?XEEQTmEBBodWdnfbeqFWHjjWhBA1D0DDutqYugxdO0QLj0DbfnRBRyTLj5Vc?= =?us-ascii?Q?PDk5tX6oU08vS+u/hVBFg8HUrcF3qepR/97gZXjGktvjJBEJr3cAk/v7xneO?= =?us-ascii?Q?0w=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: c3e413bc-a815-42b4-5a7b-08de26d003b5 X-MS-Exchange-CrossTenant-AuthSource: DM4PR11MB6117.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Nov 2025 18:26:39.3598 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: k/lX6LF4pur1J35Alf6klWBwRNXCzzj5RyMCk8+HJDpihrla+2Ne0bSW4Ehz/MbsZehhZJQoIi9Kc6lg6VKXEl1Advj6U3UPSJ0532Nql0Q= X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR11MB7752 X-OriginatorOrg: intel.com On Tue, Nov 18, 2025 at 01:48:07PM +0100, Fernando Fernandez Mancera wrote: > Since commit 30f241fcf52a ("xsk: Fix immature cq descriptor > production"), the descriptor number is stored in skb control block and > xsk_cq_submit_addr_locked() relies on it to put the umem addrs onto > pool's completion queue. > > skb control block shouldn't be used for this purpose as after transmit > xsk doesn't have control over it and other subsystems could use it. This > leads to the following kernel panic due to a NULL pointer dereference. > > BUG: kernel NULL pointer dereference, address: 0000000000000000 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: Oops: 0000 [#1] SMP NOPTI > CPU: 2 UID: 1 PID: 927 Comm: p4xsk.bin Not tainted 6.16.12+deb14-cloud-amd64 #1 PREEMPT(lazy) Debian 6.16.12-1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014 > RIP: 0010:xsk_destruct_skb+0xd0/0x180 > [...] > Call Trace: > > ? napi_complete_done+0x7a/0x1a0 > ip_rcv_core+0x1bb/0x340 > ip_rcv+0x30/0x1f0 > __netif_receive_skb_one_core+0x85/0xa0 > process_backlog+0x87/0x130 > __napi_poll+0x28/0x180 > net_rx_action+0x339/0x420 > handle_softirqs+0xdc/0x320 > ? handle_edge_irq+0x90/0x1e0 > do_softirq.part.0+0x3b/0x60 > > > __local_bh_enable_ip+0x60/0x70 > __dev_direct_xmit+0x14e/0x1f0 > __xsk_generic_xmit+0x482/0xb70 > ? __remove_hrtimer+0x41/0xa0 > ? __xsk_generic_xmit+0x51/0xb70 > ? _raw_spin_unlock_irqrestore+0xe/0x40 > xsk_sendmsg+0xda/0x1c0 > __sys_sendto+0x1ee/0x200 > __x64_sys_sendto+0x24/0x30 > do_syscall_64+0x84/0x2f0 > ? __pfx_pollwake+0x10/0x10 > ? __rseq_handle_notify_resume+0xad/0x4c0 > ? restore_fpregs_from_fpstate+0x3c/0x90 > ? switch_fpu_return+0x5b/0xe0 > ? do_syscall_64+0x204/0x2f0 > ? do_syscall_64+0x204/0x2f0 > ? do_syscall_64+0x204/0x2f0 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > > [...] > Kernel panic - not syncing: Fatal exception in interrupt > Kernel Offset: 0x1c000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) > > Instead use the skb destructor_arg pointer along with pointer tagging. > As pointers are always aligned to 8B, use the bottom bit to indicate > whether this a single address or an allocated struct containing several > addresses. > > Fixes: 30f241fcf52a ("xsk: Fix immature cq descriptor production") > Closes: https://lore.kernel.org/netdev/0435b904-f44f-48f8-afb0-68868474bf1c@nop.hu/ > Suggested-by: Jakub Kicinski > Signed-off-by: Fernando Fernandez Mancera you haven't include my ack, so: Acked-by: Maciej Fijalkowski > --- > v2: remove some leftovers on skb_build and simplify fragmented traffic > logic > > v3: drop skb extension approach, instead use pointer tagging in > destructor_arg to know whether we have a single address or an allocated > struct with multiple ones. Also, move from bpf to net as requested > > v4: repost after rebasing > --- > net/xdp/xsk.c | 130 ++++++++++++++++++++++++++++---------------------- > 1 file changed, 74 insertions(+), 56 deletions(-) > > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c > index 7b0c68a70888..d7354a3e2545 100644 > --- a/net/xdp/xsk.c > +++ b/net/xdp/xsk.c > @@ -36,20 +36,13 @@ > #define TX_BATCH_SIZE 32 > #define MAX_PER_SOCKET_BUDGET 32 > > -struct xsk_addr_node { > - u64 addr; > - struct list_head addr_node; > -}; > - > -struct xsk_addr_head { > +struct xsk_addrs { > u32 num_descs; > - struct list_head addrs_list; > + u64 addrs[MAX_SKB_FRAGS + 1]; > }; > > static struct kmem_cache *xsk_tx_generic_cache; > > -#define XSKCB(skb) ((struct xsk_addr_head *)((skb)->cb)) > - > void xsk_set_rx_need_wakeup(struct xsk_buff_pool *pool) > { > if (pool->cached_need_wakeup & XDP_WAKEUP_RX) > @@ -558,29 +551,53 @@ static int xsk_cq_reserve_locked(struct xsk_buff_pool *pool) > return ret; > } > > +static bool xsk_skb_destructor_is_addr(struct sk_buff *skb) > +{ > + return (uintptr_t)skb_shinfo(skb)->destructor_arg & 0x1UL; > +} > + > +static u64 xsk_skb_destructor_get_addr(struct sk_buff *skb) > +{ > + return (u64)((uintptr_t)skb_shinfo(skb)->destructor_arg & ~0x1UL); > +} > + > +static u32 xsk_get_num_desc(struct sk_buff *skb) > +{ > + struct xsk_addrs *xsk_addr; > + > + if (xsk_skb_destructor_is_addr(skb)) > + return 1; > + > + xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg; > + > + return xsk_addr->num_descs; > +} > + > static void xsk_cq_submit_addr_locked(struct xsk_buff_pool *pool, > struct sk_buff *skb) > { > - struct xsk_addr_node *pos, *tmp; > + u32 num_descs = xsk_get_num_desc(skb); > + struct xsk_addrs *xsk_addr; > u32 descs_processed = 0; > unsigned long flags; > - u32 idx; > + u32 idx, i; > > spin_lock_irqsave(&pool->cq_lock, flags); > idx = xskq_get_prod(pool->cq); > > - xskq_prod_write_addr(pool->cq, idx, > - (u64)(uintptr_t)skb_shinfo(skb)->destructor_arg); > - descs_processed++; > + if (unlikely(num_descs > 1)) { > + xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg; > > - if (unlikely(XSKCB(skb)->num_descs > 1)) { > - list_for_each_entry_safe(pos, tmp, &XSKCB(skb)->addrs_list, addr_node) { > + for (i = 0; i < num_descs; i++) { > xskq_prod_write_addr(pool->cq, idx + descs_processed, > - pos->addr); > + xsk_addr->addrs[i]); > descs_processed++; > - list_del(&pos->addr_node); > - kmem_cache_free(xsk_tx_generic_cache, pos); > } > + kmem_cache_free(xsk_tx_generic_cache, xsk_addr); > + } else { > + xskq_prod_write_addr(pool->cq, idx, > + xsk_skb_destructor_get_addr(skb)); > + descs_processed++; > } > xskq_prod_submit_n(pool->cq, descs_processed); > spin_unlock_irqrestore(&pool->cq_lock, flags); > @@ -595,16 +612,6 @@ static void xsk_cq_cancel_locked(struct xsk_buff_pool *pool, u32 n) > spin_unlock_irqrestore(&pool->cq_lock, flags); > } > > -static void xsk_inc_num_desc(struct sk_buff *skb) > -{ > - XSKCB(skb)->num_descs++; > -} > - > -static u32 xsk_get_num_desc(struct sk_buff *skb) > -{ > - return XSKCB(skb)->num_descs; > -} > - > static void xsk_destruct_skb(struct sk_buff *skb) > { > struct xsk_tx_metadata_compl *compl = &skb_shinfo(skb)->xsk_meta; > @@ -621,27 +628,22 @@ static void xsk_destruct_skb(struct sk_buff *skb) > static void xsk_skb_init_misc(struct sk_buff *skb, struct xdp_sock *xs, > u64 addr) > { > - BUILD_BUG_ON(sizeof(struct xsk_addr_head) > sizeof(skb->cb)); > - INIT_LIST_HEAD(&XSKCB(skb)->addrs_list); > skb->dev = xs->dev; > skb->priority = READ_ONCE(xs->sk.sk_priority); > skb->mark = READ_ONCE(xs->sk.sk_mark); > - XSKCB(skb)->num_descs = 0; > skb->destructor = xsk_destruct_skb; > - skb_shinfo(skb)->destructor_arg = (void *)(uintptr_t)addr; > + skb_shinfo(skb)->destructor_arg = (void *)((uintptr_t)addr | 0x1UL); > } > > static void xsk_consume_skb(struct sk_buff *skb) > { > struct xdp_sock *xs = xdp_sk(skb->sk); > u32 num_descs = xsk_get_num_desc(skb); > - struct xsk_addr_node *pos, *tmp; > + struct xsk_addrs *xsk_addr; > > if (unlikely(num_descs > 1)) { > - list_for_each_entry_safe(pos, tmp, &XSKCB(skb)->addrs_list, addr_node) { > - list_del(&pos->addr_node); > - kmem_cache_free(xsk_tx_generic_cache, pos); > - } > + xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg; > + kmem_cache_free(xsk_tx_generic_cache, xsk_addr); > } > > skb->destructor = sock_wfree; > @@ -701,7 +703,6 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, > { > struct xsk_buff_pool *pool = xs->pool; > u32 hr, len, ts, offset, copy, copied; > - struct xsk_addr_node *xsk_addr; > struct sk_buff *skb = xs->skb; > struct page *page; > void *buffer; > @@ -727,16 +728,27 @@ static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs, > return ERR_PTR(err); > } > } else { > - xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache, GFP_KERNEL); > - if (!xsk_addr) > - return ERR_PTR(-ENOMEM); > + struct xsk_addrs *xsk_addr; > + > + if (xsk_skb_destructor_is_addr(skb)) { > + xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache, > + GFP_KERNEL); > + if (!xsk_addr) > + return ERR_PTR(-ENOMEM); > + > + xsk_addr->num_descs = 1; > + xsk_addr->addrs[0] = xsk_skb_destructor_get_addr(skb); > + skb_shinfo(skb)->destructor_arg = (void *)xsk_addr; > + } else { > + xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg; > + } > > /* in case of -EOVERFLOW that could happen below, > * xsk_consume_skb() will release this node as whole skb > * would be dropped, which implies freeing all list elements > */ > - xsk_addr->addr = desc->addr; > - list_add_tail(&xsk_addr->addr_node, &XSKCB(skb)->addrs_list); > + xsk_addr->addrs[xsk_addr->num_descs] = desc->addr; > + xsk_addr->num_descs++; > } > > len = desc->len; > @@ -813,7 +825,7 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, > } > } else { > int nr_frags = skb_shinfo(skb)->nr_frags; > - struct xsk_addr_node *xsk_addr; > + struct xsk_addrs *xsk_addr; > struct page *page; > u8 *vaddr; > > @@ -828,11 +840,20 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, > goto free_err; > } > > - xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache, GFP_KERNEL); > - if (!xsk_addr) { > - __free_page(page); > - err = -ENOMEM; > - goto free_err; > + if (xsk_skb_destructor_is_addr(skb)) { > + xsk_addr = kmem_cache_zalloc(xsk_tx_generic_cache, > + GFP_KERNEL); > + if (!xsk_addr) { > + __free_page(page); > + err = -ENOMEM; > + goto free_err; > + } > + > + xsk_addr->num_descs = 1; > + xsk_addr->addrs[0] = xsk_skb_destructor_get_addr(skb); > + skb_shinfo(skb)->destructor_arg = (void *)xsk_addr; > + } else { > + xsk_addr = (struct xsk_addrs *)skb_shinfo(skb)->destructor_arg; > } > > vaddr = kmap_local_page(page); > @@ -842,13 +863,11 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, > skb_add_rx_frag(skb, nr_frags, page, 0, len, PAGE_SIZE); > refcount_add(PAGE_SIZE, &xs->sk.sk_wmem_alloc); > > - xsk_addr->addr = desc->addr; > - list_add_tail(&xsk_addr->addr_node, &XSKCB(skb)->addrs_list); > + xsk_addr->addrs[xsk_addr->num_descs] = desc->addr; > + xsk_addr->num_descs++; > } > } > > - xsk_inc_num_desc(skb); > - > return skb; > > free_err: > @@ -857,7 +876,6 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs, > > if (err == -EOVERFLOW) { > /* Drop the packet */ > - xsk_inc_num_desc(xs->skb); > xsk_drop_skb(xs->skb); > xskq_cons_release(xs->tx); > } else { > @@ -1904,7 +1922,7 @@ static int __init xsk_init(void) > goto out_pernet; > > xsk_tx_generic_cache = kmem_cache_create("xsk_generic_xmit_cache", > - sizeof(struct xsk_addr_node), > + sizeof(struct xsk_addrs), > 0, SLAB_HWCACHE_ALIGN, NULL); > if (!xsk_tx_generic_cache) { > err = -ENOMEM; > -- > 2.51.1 >