Subject: [syzbot] [bpf?] [net?] stack segment fault in cpu_map_redirect

From: syzbot <[email-masked]>
Date: Tue, 09 Jul 2024 10:09:22 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    0b58e108042b Add linux-next specific files for 20240703
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17a85c9e980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ed034204f2e40e53
dashboard link: https://syzkaller.appspot.com/bug?extid=6fc359860535c8a466fa
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14aca369980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11a6f6e1980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1d079762feae/disk-0b58e108.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e53996c8d8c2/vmlinux-0b58e108.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a0bf21cdd844/bzImage-0b58e108.xz

The issue was bisected to:

commit 401cb7dae8130fd34eb84648e02ab4c506df7d5e
Author: Sebastian Andrzej Siewior <[email-masked]>
Date:   Thu Jun 20 13:22:04 2024 +0000

    net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16373059980000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=15373059980000
console output: https://syzkaller.appspot.com/x/log.txt?x=11373059980000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]
Fixes: 401cb7dae813 ("net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.")

Oops: stack segment: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 UID: 0 PID: 5103 Comm: syz-executor681 Not tainted 6.10.0-rc6-next-20240703-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
RIP: 0010:bpf_net_ctx_get_ri include/linux/filter.h:788 [inline]
RIP: 0010:__bpf_xdp_redirect_map include/linux/filter.h:1699 [inline]
RIP: 0010:cpu_map_redirect+0x5c/0x470 kernel/bpf/cpumap.c:643
Code: 81 c3 00 18 00 00 48 89 d8 48 c1 e8 03 42 80 3c 30 00 74 08 48 89 df e8 62 6b 3d 00 4c 8b 2b 49 8d 5d 38 48 89 dd 48 c1 ed 03 <42> 0f b6 44 35 00 84 c0 0f 85 fd 02 00 00 44 8b 33 44 89 f6 83 e6
RSP: 0018:ffffc9000395f960 EFLAGS: 00010202
RAX: 1ffff110051dd300 RBX: 0000000000000038 RCX: ffff888028ee8000
RDX: 0000000000000000 RSI: 000000000395f9b0 RDI: ffff88802ec3fc00
RBP: 0000000000000007 R08: 0000000000000007 R09: ffffffff81b5ee2f
R10: 0000000000000004 R11: ffff888028ee8000 R12: 000000000395f9b0
R13: 0000000000000000 R14: dffffc0000000000 R15: ffff88802ec3fc00
FS:  000055556a17a380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000099d4b98 CR3: 0000000021f40000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 bpf_prog_ec9efaa32d58ce69+0x56/0x5a
 __bpf_prog_run include/linux/filter.h:691 [inline]
 bpf_prog_run_xdp include/net/xdp.h:514 [inline]
 tun_build_skb drivers/net/tun.c:1711 [inline]
 tun_get_user+0x3321/0x4560 drivers/net/tun.c:1819
 tun_chr_write_iter+0x113/0x1f0 drivers/net/tun.c:2048
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0xa72/0xc90 fs/read_write.c:590
 ksys_write+0x1a0/0x2c0 fs/read_write.c:643
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f40ef4f8070
Code: 40 00 48 c7 c2 b8 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 80 3d 51 e0 07 00 00 74 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 48 89
RSP: 002b:00007ffcf4c50d48 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f40ef4f8070
RDX: 0000000000000022 RSI: 0000000020000a40 RDI: 00000000000000c8
RBP: 0000000000000000 R08: 00007ffc0000000d R09: 00007ffc0000000d
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:bpf_net_ctx_get_ri include/linux/filter.h:788 [inline]
RIP: 0010:__bpf_xdp_redirect_map include/linux/filter.h:1699 [inline]
RIP: 0010:cpu_map_redirect+0x5c/0x470 kernel/bpf/cpumap.c:643
Code: 81 c3 00 18 00 00 48 89 d8 48 c1 e8 03 42 80 3c 30 00 74 08 48 89 df e8 62 6b 3d 00 4c 8b 2b 49 8d 5d 38 48 89 dd 48 c1 ed 03 <42> 0f b6 44 35 00 84 c0 0f 85 fd 02 00 00 44 8b 33 44 89 f6 83 e6
RSP: 0018:ffffc9000395f960 EFLAGS: 00010202
RAX: 1ffff110051dd300 RBX: 0000000000000038 RCX: ffff888028ee8000
RDX: 0000000000000000 RSI: 000000000395f9b0 RDI: ffff88802ec3fc00
RBP: 0000000000000007 R08: 0000000000000007 R09: ffffffff81b5ee2f
R10: 0000000000000004 R11: ffff888028ee8000 R12: 000000000395f9b0
R13: 0000000000000000 R14: dffffc0000000000 R15: ffff88802ec3fc00
FS:  000055556a17a380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000099d4b98 CR3: 0000000021f40000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	81 c3 00 18 00 00    	add    $0x1800,%ebx
   6:	48 89 d8             	mov    %rbx,%rax
   9:	48 c1 e8 03          	shr    $0x3,%rax
   d:	42 80 3c 30 00       	cmpb   $0x0,(%rax,%r14,1)
  12:	74 08                	je     0x1c
  14:	48 89 df             	mov    %rbx,%rdi
  17:	e8 62 6b 3d 00       	call   0x3d6b7e
  1c:	4c 8b 2b             	mov    (%rbx),%r13
  1f:	49 8d 5d 38          	lea    0x38(%r13),%rbx
  23:	48 89 dd             	mov    %rbx,%rbp
  26:	48 c1 ed 03          	shr    $0x3,%rbp
* 2a:	42 0f b6 44 35 00    	movzbl 0x0(%rbp,%r14,1),%eax <-- trapping instruction
  30:	84 c0                	test   %al,%al
  32:	0f 85 fd 02 00 00    	jne    0x335
  38:	44 8b 33             	mov    (%rbx),%r14d
  3b:	44 89 f6             	mov    %r14d,%esi
  3e:	83                   	.byte 0x83
  3f:	e6                   	.byte 0xe6

---
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