CVE-2025-39984

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net: tun: Update napi-&gt;skb after XDP process<br /> <br /> The syzbot report a UAF issue:<br /> <br /> BUG: KASAN: slab-use-after-free in skb_reset_mac_header include/linux/skbuff.h:3150 [inline]<br /> BUG: KASAN: slab-use-after-free in napi_frags_skb net/core/gro.c:723 [inline]<br /> BUG: KASAN: slab-use-after-free in napi_gro_frags+0x6e/0x1030 net/core/gro.c:758<br /> Read of size 8 at addr ffff88802ef22c18 by task syz.0.17/6079<br /> CPU: 0 UID: 0 PID: 6079 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)<br /> Call Trace:<br /> <br /> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120<br /> print_address_description mm/kasan/report.c:378 [inline]<br /> print_report+0xca/0x240 mm/kasan/report.c:482<br /> kasan_report+0x118/0x150 mm/kasan/report.c:595<br /> skb_reset_mac_header include/linux/skbuff.h:3150 [inline]<br /> napi_frags_skb net/core/gro.c:723 [inline]<br /> napi_gro_frags+0x6e/0x1030 net/core/gro.c:758<br /> tun_get_user+0x28cb/0x3e20 drivers/net/tun.c:1920<br /> tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1996<br /> new_sync_write fs/read_write.c:593 [inline]<br /> vfs_write+0x5c9/0xb30 fs/read_write.c:686<br /> ksys_write+0x145/0x250 fs/read_write.c:738<br /> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]<br /> do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94<br /> entry_SYSCALL_64_after_hwframe+0x77/0x7f<br /> <br /> <br /> Allocated by task 6079:<br /> kasan_save_stack mm/kasan/common.c:47 [inline]<br /> kasan_save_track+0x3e/0x80 mm/kasan/common.c:68<br /> unpoison_slab_object mm/kasan/common.c:330 [inline]<br /> __kasan_mempool_unpoison_object+0xa0/0x170 mm/kasan/common.c:558<br /> kasan_mempool_unpoison_object include/linux/kasan.h:388 [inline]<br /> napi_skb_cache_get+0x37b/0x6d0 net/core/skbuff.c:295<br /> __alloc_skb+0x11e/0x2d0 net/core/skbuff.c:657<br /> napi_alloc_skb+0x84/0x7d0 net/core/skbuff.c:811<br /> napi_get_frags+0x69/0x140 net/core/gro.c:673<br /> tun_napi_alloc_frags drivers/net/tun.c:1404 [inline]<br /> tun_get_user+0x77c/0x3e20 drivers/net/tun.c:1784<br /> tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1996<br /> new_sync_write fs/read_write.c:593 [inline]<br /> vfs_write+0x5c9/0xb30 fs/read_write.c:686<br /> ksys_write+0x145/0x250 fs/read_write.c:738<br /> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]<br /> do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94<br /> entry_SYSCALL_64_after_hwframe+0x77/0x7f<br /> <br /> Freed by task 6079:<br /> kasan_save_stack mm/kasan/common.c:47 [inline]<br /> kasan_save_track+0x3e/0x80 mm/kasan/common.c:68<br /> kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576<br /> poison_slab_object mm/kasan/common.c:243 [inline]<br /> __kasan_slab_free+0x5b/0x80 mm/kasan/common.c:275<br /> kasan_slab_free include/linux/kasan.h:233 [inline]<br /> slab_free_hook mm/slub.c:2422 [inline]<br /> slab_free mm/slub.c:4695 [inline]<br /> kmem_cache_free+0x18f/0x400 mm/slub.c:4797<br /> skb_pp_cow_data+0xdd8/0x13e0 net/core/skbuff.c:969<br /> netif_skb_check_for_xdp net/core/dev.c:5390 [inline]<br /> netif_receive_generic_xdp net/core/dev.c:5431 [inline]<br /> do_xdp_generic+0x699/0x11a0 net/core/dev.c:5499<br /> tun_get_user+0x2523/0x3e20 drivers/net/tun.c:1872<br /> tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1996<br /> new_sync_write fs/read_write.c:593 [inline]<br /> vfs_write+0x5c9/0xb30 fs/read_write.c:686<br /> ksys_write+0x145/0x250 fs/read_write.c:738<br /> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]<br /> do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94<br /> entry_SYSCALL_64_after_hwframe+0x77/0x7f<br /> <br /> After commit e6d5dbdd20aa ("xdp: add multi-buff support for xdp running in<br /> generic mode"), the original skb may be freed in skb_pp_cow_data() when<br /> XDP program was attached, which was allocated in tun_napi_alloc_frags().<br /> However, the napi-&gt;skb still point to the original skb, update it after<br /> XDP process.