Messages in this thread Patch in this message | | | From | Andrew Kanner <> | Subject | [PATCH v3] drivers: net: prevent tun_get_user() to exceed xdp size limits | Date | Tue, 25 Jul 2023 18:54:04 +0300 |
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Syzkaller reported the following issue: ======================================= Too BIG xdp->frame_sz = 131072 WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121 ____bpf_xdp_adjust_tail net/core/filter.c:4121 [inline] WARNING: CPU: 0 PID: 5020 at net/core/filter.c:4121 bpf_xdp_adjust_tail+0x466/0xa10 net/core/filter.c:4103 ... Call Trace: <TASK> bpf_prog_4add87e5301a4105+0x1a/0x1c __bpf_prog_run include/linux/filter.h:600 [inline] bpf_prog_run_xdp include/linux/filter.h:775 [inline] bpf_prog_run_generic_xdp+0x57e/0x11e0 net/core/dev.c:4721 netif_receive_generic_xdp net/core/dev.c:4807 [inline] do_xdp_generic+0x35c/0x770 net/core/dev.c:4866 tun_get_user+0x2340/0x3ca0 drivers/net/tun.c:1919 tun_chr_write_iter+0xe8/0x210 drivers/net/tun.c:2043 call_write_iter include/linux/fs.h:1871 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x650/0xe40 fs/read_write.c:584 ksys_write+0x12f/0x250 fs/read_write.c:637 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
xdp->frame_sz > PAGE_SIZE check was introduced in commit c8741e2bfe87 ("xdp: Allow bpf_xdp_adjust_tail() to grow packet size"). But tun_get_user() still provides an execution path with do_xdp_generic() and exceed XDP limits for packet size.
Using the syzkaller repro with reduced packet size it was also discovered that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(), although pad may be incremented in tun_build_skb().
If we move the limit check from tun_can_build_skb() to tun_build_skb() we will make xdp to be used only in tun_build_skb(), without falling in tun_alloc_skb(), etc. And moreover we will drop the packet which can't be processed in tun_build_skb().
Reported-and-tested-by: syzbot+f817490f5bd20541b90a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000774b9205f1d8a80d@google.com/T/ Link: https://syzkaller.appspot.com/bug?id=5335c7c62bfff89bbb1c8f14cdabebe91909060f Fixes: 7df13219d757 ("tun: reserve extra headroom only when XDP is set") Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com> ---
Notes: V2 -> V3: * attach the forgotten changelog V1 -> V2: * merged 2 patches in 1, fixing both issues: WARN_ON_ONCE with syzkaller repro and missing XDP_PACKET_HEADROOM in pad * changed the title and description of the execution path, suggested by Jason Wang <jasowang@redhat.com> * move the limit check from tun_can_build_skb() to tun_build_skb() to remove duplication and locking issue, and also drop the packet in case of a failed check - noted by Jason Wang <jasowang@redhat.com>
drivers/net/tun.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index d75456adc62a..7c2b05ce0421 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1594,10 +1594,6 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile, if (zerocopy) return false; - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) + - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE) - return false; - return true; } @@ -1673,6 +1669,9 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, buflen += SKB_DATA_ALIGN(len + pad); rcu_read_unlock(); + if (buflen > PAGE_SIZE) + return ERR_PTR(-EFAULT); + alloc_frag->offset = ALIGN((u64)alloc_frag->offset, SMP_CACHE_BYTES); if (unlikely(!skb_page_frag_refill(buflen, alloc_frag, GFP_KERNEL))) return ERR_PTR(-ENOMEM); -- 2.39.3
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