Messages in this thread Patch in this message | | | Date | Thu, 3 Dec 2020 16:58:19 +0100 | From | Marco Elver <> | Subject | Re: WARNING in sk_stream_kill_queues (5) |
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On Mon, Nov 30, 2020 at 12:40AM -0800, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 6147c83f Add linux-next specific files for 20201126 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=117c9679500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=9b91566da897c24f > dashboard link: https://syzkaller.appspot.com/bug?extid=7b99aafdcc2eedea6178 > compiler: gcc (GCC) 10.1.0-syz 20200507 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=103bf743500000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=167c60c9500000 > > The issue was bisected to: > > commit 145cd60fb481328faafba76842aa0fd242e2b163 > Author: Alexander Potapenko <glider@google.com> > Date: Tue Nov 24 05:38:44 2020 +0000 > > mm, kfence: insert KFENCE hooks for SLUB > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13abe5b3500000 > final oops: https://syzkaller.appspot.com/x/report.txt?x=106be5b3500000 > console output: https://syzkaller.appspot.com/x/log.txt?x=17abe5b3500000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+7b99aafdcc2eedea6178@syzkaller.appspotmail.com > Fixes: 145cd60fb481 ("mm, kfence: insert KFENCE hooks for SLUB") > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 11307 at net/core/stream.c:207 sk_stream_kill_queues+0x3c3/0x530 net/core/stream.c:207 [...] > Call Trace: > inet_csk_destroy_sock+0x1a5/0x490 net/ipv4/inet_connection_sock.c:885 > __tcp_close+0xd3e/0x1170 net/ipv4/tcp.c:2585 > tcp_close+0x29/0xc0 net/ipv4/tcp.c:2597 > inet_release+0x12e/0x280 net/ipv4/af_inet.c:431 > __sock_release+0xcd/0x280 net/socket.c:596 > sock_close+0x18/0x20 net/socket.c:1255 > __fput+0x283/0x920 fs/file_table.c:280 > task_work_run+0xdd/0x190 kernel/task_work.c:140 > exit_task_work include/linux/task_work.h:30 [inline] > do_exit+0xb89/0x29e0 kernel/exit.c:823 > do_group_exit+0x125/0x310 kernel/exit.c:920 > get_signal+0x3ec/0x2010 kernel/signal.c:2770 > arch_do_signal_or_restart+0x2a8/0x1eb0 arch/x86/kernel/signal.c:811 > handle_signal_work kernel/entry/common.c:144 [inline] > exit_to_user_mode_loop kernel/entry/common.c:168 [inline] > exit_to_user_mode_prepare+0x124/0x200 kernel/entry/common.c:198 > syscall_exit_to_user_mode+0x36/0x260 kernel/entry/common.c:275 > entry_SYSCALL_64_after_hwframe+0x44/0xa9
I've been debugging this and I think enabling KFENCE uncovered that some code is assuming that the following is always true:
ksize(kmalloc(S)) == ksize(kmalloc(S))
but I don't think this assumption can be made (with or without KFENCE).
With KFENCE, we actually end up testing no code assumes this, because KFENCE's ksize() always returns the exact size S.
I have narrowed it down to sk_wmem_queued becoming <0 in sk_wmem_free_skb().
The skb passed to sk_wmem_free_skb() and whose truesize causes sk_wmem_queued to become negative is always allocated in:
| kmem_cache_alloc_node+0x140/0x400 mm/slub.c:2939 | __alloc_skb+0x6d/0x710 net/core/skbuff.c:198 | alloc_skb_fclone include/linux/skbuff.h:1144 [inline] | sk_stream_alloc_skb+0x109/0xc30 net/ipv4/tcp.c:888 | tso_fragment net/ipv4/tcp_output.c:2124 [inline] | tcp_write_xmit+0x1dbf/0x5ce0 net/ipv4/tcp_output.c:2674 | __tcp_push_pending_frames+0xaa/0x390 net/ipv4/tcp_output.c:2866 | tcp_push_pending_frames include/net/tcp.h:1864 [inline] | tcp_data_snd_check net/ipv4/tcp_input.c:5374 [inline] | tcp_rcv_established+0x8c9/0x1eb0 net/ipv4/tcp_input.c:5869 | tcp_v4_do_rcv+0x5d1/0x870 net/ipv4/tcp_ipv4.c:1668 | sk_backlog_rcv include/net/sock.h:1011 [inline] | __release_sock+0x134/0x3a0 net/core/sock.c:2523 | release_sock+0x54/0x1b0 net/core/sock.c:3053 | sk_wait_data+0x177/0x450 net/core/sock.c:2565 | tcp_recvmsg+0x17ea/0x2aa0 net/ipv4/tcp.c:2181 | inet_recvmsg+0x11b/0x5d0 net/ipv4/af_inet.c:848 | sock_recvmsg_nosec net/socket.c:885 [inline] | sock_recvmsg net/socket.c:903 [inline] | sock_recvmsg net/socket.c:899 [inline] | ____sys_recvmsg+0x2c4/0x600 net/socket.c:2563 | ___sys_recvmsg+0x127/0x200 net/socket.c:2605 | __sys_recvmsg+0xe2/0x1a0 net/socket.c:2641 | do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 | entry_SYSCALL_64_after_hwframe+0x44/0xa9
I used the code below to add some warnings that helped narrow it down.
Does any of this help explain the problem?
Thanks, -- Marco
------ >8 ------
diff --git a/include/net/sock.h b/include/net/sock.h index e8d958ef3ea0..ef4837f3aba4 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -35,6 +35,7 @@ #ifndef _SOCK_H #define _SOCK_H +#include <linux/kfence.h> #include <linux/hardirq.h> #include <linux/kernel.h> #include <linux/list.h> @@ -1534,7 +1535,15 @@ static inline void sk_mem_uncharge(struct sock *sk, int size) DECLARE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key); static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb) { + bool bad = false; + sk_wmem_queued_add(sk, -skb->truesize); + + if (WARN_ON(READ_ONCE(sk->sk_wmem_queued) == -384)) { + pr_info("wmem_queued=%d truesize=%u\n", sk->sk_wmem_queued, skb->truesize); + bad = true; + } + sk_mem_uncharge(sk, skb->truesize); if (static_branch_unlikely(&tcp_tx_skb_cache_key) && !sk->sk_tx_skb_cache && !skb_cloned(skb)) { @@ -1544,6 +1553,9 @@ static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb) return; } __kfree_skb(skb); + + if (bad) + (void)READ_ONCE(skb->truesize); /* UAF to let KASAN show where it was allocated */ } static inline void sock_release_ownership(struct sock *sk) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index ffe3dcc0ebea..f365495819ee 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -208,6 +208,19 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, size = SKB_DATA_ALIGN(size); size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc); + + if (is_kfence_address(data)) + pr_info("kfence's ksize: %zu\n", ksize(data)); + /* + * BUG BUG + * Hypothesis: The problem is that some code assumes that: + * + * ksize(kmalloc(S)) == ksize(kmalloc(S)) + * + * Note: If we force no KFENCE allocation for @data above, the warnings + * disappear. KFENCE's ksize() always returns the exact size S. + */ + if (!data) goto nodata; /* kmalloc(size) might give us more room than requested.
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