CVE-2024-49949: In the Linux kernel, the following vulnerability has been resolved:  net: avoid potential underflow in qdisc_pkt_len_init() with UFO  After commit 7c6d2ecbda83 ("net: be more gentle about silly gso requests coming from user") virtio_net_hdr_to_skb() had sanity check to detect malicious attempts from user space to cook a bad GSO packet.  Then commit cf9acc90c80ec ("net: virtio_net_hdr_to_skb: count transport header in UFO") while fixing one issue, allowed user space to cook a GSO packet with the following characteristic :  IPv4 SKB_GSO_UDP, gso_size=3, skb->len = 28.  When this packet arrives in qdisc_pkt_len_init(), we end up with hdr_len = 28 (IPv4 header + UDP header), matching skb->len  Then the following sets gso_segs to 0 :  gso_segs = DIV_ROUND_UP(skb->len - hdr_len,                         shinfo->gso_size);  Then later we set qdisc_skb_cb(skb)->pkt_len to back to zero :/  qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len;  This leads to the following crash in fq_codel [1]  qdisc_pkt_len_init() is best effort, we only want an estimation of the bytes sent on the wire, not crashing the kernel.  This patch is fixing this particular issue, a following one adds more sanity checks for another potential bug.  [1] [   70.724101] BUG: kernel NULL pointer dereference, address: 0000000000000000 [   70.724561] #PF: supervisor read access in kernel mode [   70.724561] #PF: error_code(0x0000) - not-present page [   70.724561] PGD 10ac61067 P4D 10ac61067 PUD 107ee2067 PMD 0 [   70.724561] Oops: Oops: 0000 [#1] SMP NOPTI [   70.724561] CPU: 11 UID: 0 PID: 2163 Comm: b358537762 Not tainted 6.11.0-virtme #991 [   70.724561] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [   70.724561] RIP: 0010:fq_codel_enqueue (net/sched/sch_fq_codel.c:120 net/sched/sch_fq_codel.c:168 net/sched/sch_fq_codel.c:230) sch_fq_codel [ 70.724561] Code: 24 08 49 c1 e1 06 44 89 7c 24 18 45 31 ed 45 31 c0 31 ff 89 44 24 14 4c 03 8b 90 01 00 00 eb 04 39 ca 73 37 4d 8b 39 83 c7 01 <49> 8b 17 49 89 11 41 8b 57 28 45 8b 5f 34 49 c7 07 00 00 00 00 49 All code ========    0: 24 08                 and    $0x8,%al    2: 49 c1 e1 06           shl    $0x6,%r9    6: 44 89 7c 24 18        mov    %r15d,0x18(%rsp)    b: 45 31 ed              xor    %r13d,%r13d    e: 45 31 c0              xor    %r8d,%r8d   11: 31 ff                 xor    %edi,%edi   13: 89 44 24 14           mov    %eax,0x14(%rsp)   17: 4c 03 8b 90 01 00 00  add    0x190(%rbx),%r9   1e: eb 04                 jmp    0x24   20: 39 ca                 cmp    %ecx,%edx   22: 73 37                 jae    0x5b   24: 4d 8b 39              mov    (%r9),%r15   27: 83 c7 01              add    $0x1,%edi   2a:* 49 8b 17              mov    (%r15),%rdx  <-- trapping instruction   2d: 49 89 11              mov    %rdx,(%r9)   30: 41 8b 57 28           mov    0x28(%r15),%edx   34: 45 8b 5f 34           mov    0x34(%r15),%r11d   38: 49 c7 07 00 00 00 00  movq   $0x0,(%r15)   3f: 49                    rex.WB  Code starting with the faulting instruction ===========================================    0: 49 8b 17              mov    (%r15),%rdx    3: 49 89 11              mov    %rdx,(%r9)    6: 41 8b 57 28           mov    0x28(%r15),%edx    a: 45 8b 5f 34           mov    0x34(%r15),%r11d    e: 49 c7 07 00 00 00 00  movq   $0x0,(%r15)   15: 49                    rex.WB [   70.724561] RSP: 0018:ffff95ae85e6fb90 EFLAGS: 00000202 [   70.724561] RAX: 0000000002000000 RBX: ffff95ae841de000 RCX: 0000000000000000 [   70.724561] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000001 [   70.724561] RBP: ffff95ae85e6fbf8 R08: 0000000000000000 R09: ffff95b710a30000 [   70.724561] R10: 0000000000000000 R11: bdf289445ce31881 R12: ffff95ae85e6fc58 [   70.724561] R13: 0000000000000000 R14: 0000000000000040 R15: 0000000000000000 [   70.724561] FS:  000000002c5c1380(0000) GS:ffff95bd7fcc0000(0000) knlGS:0000000000000000 [   70.724561] CS:  0010 DS: 0000 ES: 0000 C ---truncated---