Subject: [syzbot] KMSAN: uninit-value in p9pdu_readf

From: syzbot <[email-masked]>
Date: Sat, 09 Oct 2021 22:48:17 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    c7f84f4e1147 kmsan: core: do not touch interrupts when ent..
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=118e86a8b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=978f1b2d7a5aad3e
dashboard link: https://syzkaller.appspot.com/bug?extid=06472778c97ed94af66d
compiler:       clang version 14.0.0 ([email-masked]:llvm/llvm-project.git 0996585c8e3b3d409494eb5f1cad714b9e1f7fb5), GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

=====================================================
BUG: KMSAN: uninit-value in p9pdu_vreadf net/9p/protocol.c:147 [inline]
BUG: KMSAN: uninit-value in p9pdu_readf+0x46cf/0x4fc0 net/9p/protocol.c:526
 p9pdu_vreadf net/9p/protocol.c:147 [inline]
 p9pdu_readf+0x46cf/0x4fc0 net/9p/protocol.c:526
 p9pdu_vreadf net/9p/protocol.c:198 [inline]
 p9pdu_readf+0x2080/0x4fc0 net/9p/protocol.c:526
 p9_client_stat+0x2b3/0x710 net/9p/client.c:1724
 v9fs_mount+0xc14/0x12c0 fs/9p/vfs_super.c:170
 legacy_get_tree+0x163/0x2e0 fs/fs_context.c:610
 vfs_get_tree+0xd8/0x5d0 fs/super.c:1498
 do_new_mount+0x7bc/0x1680 fs/namespace.c:2988
 path_mount+0x106f/0x2960 fs/namespace.c:3318
 do_mount fs/namespace.c:3331 [inline]
 __do_sys_mount fs/namespace.c:3539 [inline]
 __se_sys_mount+0x8eb/0xa10 fs/namespace.c:3516
 __ia32_sys_mount+0x157/0x1b0 fs/namespace.c:3516
 do_syscall_32_irqs_on arch/x86/entry/common.c:114 [inline]
 __do_fast_syscall_32+0x96/0xf0 arch/x86/entry/common.c:180
 do_fast_syscall_32+0x34/0x70 arch/x86/entry/common.c:205
 do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:248
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c

Local variable ----ecode@p9_check_errors created at:
 p9_check_errors+0x68/0xb90 net/9p/client.c:506
 p9_client_rpc+0xd90/0x1410 net/9p/client.c:801
=====================================================
Kernel panic - not syncing: panic_on_kmsan set ...
CPU: 0 PID: 31201 Comm: syz-executor.3 Tainted: G    B   W         5.15.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1ff/0x28e lib/dump_stack.c:106
 dump_stack+0x25/0x28 lib/dump_stack.c:113
 panic+0x44f/0xdeb kernel/panic.c:232
 kmsan_report+0x2ee/0x300 mm/kmsan/report.c:168
 __msan_warning+0xa9/0xf0 mm/kmsan/instrumentation.c:199
 p9pdu_vreadf net/9p/protocol.c:147 [inline]
 p9pdu_readf+0x46cf/0x4fc0 net/9p/protocol.c:526
 p9pdu_vreadf net/9p/protocol.c:198 [inline]
 p9pdu_readf+0x2080/0x4fc0 net/9p/protocol.c:526
 p9_client_stat+0x2b3/0x710 net/9p/client.c:1724
 v9fs_mount+0xc14/0x12c0 fs/9p/vfs_super.c:170
 legacy_get_tree+0x163/0x2e0 fs/fs_context.c:610
 vfs_get_tree+0xd8/0x5d0 fs/super.c:1498
 do_new_mount+0x7bc/0x1680 fs/namespace.c:2988
 path_mount+0x106f/0x2960 fs/namespace.c:3318
 do_mount fs/namespace.c:3331 [inline]
 __do_sys_mount fs/namespace.c:3539 [inline]
 __se_sys_mount+0x8eb/0xa10 fs/namespace.c:3516
 __ia32_sys_mount+0x157/0x1b0 fs/namespace.c:3516
 do_syscall_32_irqs_on arch/x86/entry/common.c:114 [inline]
 __do_fast_syscall_32+0x96/0xf0 arch/x86/entry/common.c:180
 do_fast_syscall_32+0x34/0x70 arch/x86/entry/common.c:205
 do_SYSENTER_32+0x1b/0x20 arch/x86/entry/common.c:248
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf6ef3549
Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00
RSP: 002b:00000000f44ed5fc EFLAGS: 00000296 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000020000000
RDX: 0000000020000140 RSI: 0000000000000000 RDI: 0000000020000580
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Kernel Offset: disabled
Rebooting in 86400 seconds..
----------------
Code disassembly (best guess):
   0:	03 74 c0 01          	add    0x1(%rax,%rax,8),%esi
   4:	10 05 03 74 b8 01    	adc    %al,0x1b87403(%rip)        # 0x1b8740d
   a:	10 06                	adc    %al,(%rsi)
   c:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
  10:	10 07                	adc    %al,(%rdi)
  12:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
  16:	10 08                	adc    %cl,(%rax)
  18:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
  1c:	00 00                	add    %al,(%rax)
  1e:	00 00                	add    %al,(%rax)
  20:	00 51 52             	add    %dl,0x52(%rcx)
  23:	55                   	push   %rbp
  24:	89 e5                	mov    %esp,%ebp
  26:	0f 34                	sysenter
  28:	cd 80                	int    $0x80
* 2a:	5d                   	pop    %rbp <-- trapping instruction
  2b:	5a                   	pop    %rdx
  2c:	59                   	pop    %rcx
  2d:	c3                   	retq
  2e:	90                   	nop
  2f:	90                   	nop
  30:	90                   	nop
  31:	90                   	nop
  32:	66 2e 0f 1f 84 00 00 	nopw   %cs:0x0(%rax,%rax,1)
  39:	00 00 00
  3c:	0f                   	.byte 0xf
  3d:	1f                   	(bad)
  3e:	44                   	rex.R

---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email-masked].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.