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SubjectBUG: unable to handle kernel NULL pointer dereference in __syscall_return_slowpath
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Hello,

syzbot found the following crash on:

HEAD commit: 4e99b321 Merge tag 'nfs-for-5.8-2' of git://git.linux-nfs...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=116abdd3100000
kernel config: https://syzkaller.appspot.com/x/.config?x=bf3aec367b9ab569
dashboard link: https://syzkaller.appspot.com/bug?extid=95910cea1a7ad8850a0f
compiler: gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17020755100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+95910cea1a7ad8850a0f@syzkaller.appspotmail.com

BUG: kernel NULL pointer dereference, address: 000000000000000f
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8079 Comm: systemd-udevd Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__syscall_return_slowpath+0x0/0x280 arch/x86/entry/common.c:309
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
RSP: 0018:ffffc90004cd7f38 EFLAGS: 00010283
RAX: 000000000000000f RBX: 0000000000000002 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff81bc66f2 RDI: ffffc90004cd7f58
RBP: ffffc90004cd7f58 R08: 0000000000000000 R09: ffff8880ae636cdb
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 00007f934b3b78c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000000000f CR3: 000000008ebc4000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
do_syscall_64+0x6c/0xe0 arch/x86/entry/common.c:368
entry_SYSCALL_64_after_hwframe+0x44/0xa9
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0
Oops: 0002 [#2] PREEMPT SMP KASAN
CPU: 0 PID: 8079 Comm: systemd-udevd Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:in_gate_area_no_mm+0x0/0x6a arch/x86/entry/vsyscall/vsyscall_64.c:343
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
RSP: 0018:ffffc90004cd7478 EFLAGS: 00010093
RAX: 0000000000000000 RBX: ffffc90004cd7518 RCX: ffffffff8169f800
RDX: ffff888091d90300 RSI: ffffffff8169f82b RDI: 00007f934a4fe840
RBP: 00007f934a4fe840 R08: ffffc90004cd7628 R09: ffffffff8c8c8109
R10: 00007f934a4fe840 R11: 0000000000000000 R12: ffffc90004cd7628
R13: 0000000000000001 R14: 00007f934a4fe840 R15: ffffc90004cd7538
FS: 00007f934b3b78c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000008ebc4000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
is_kernel include/linux/kallsyms.h:43 [inline]
is_ksym_addr include/linux/kallsyms.h:49 [inline]
kallsyms_lookup+0xc3/0x2e0 kernel/kallsyms.c:290
__sprint_symbol+0x9c/0x1c0 kernel/kallsyms.c:363
symbol_string+0x14c/0x370 lib/vsprintf.c:969
pointer+0x185/0x970 lib/vsprintf.c:2226
vsnprintf+0x5b2/0x14f0 lib/vsprintf.c:2624
vscnprintf+0x29/0x80 lib/vsprintf.c:2723
vprintk_store+0x44/0x4a0 kernel/printk/printk.c:1942
vprintk_emit+0x139/0x770 kernel/printk/printk.c:2003
vprintk_func+0x8f/0x1a6 kernel/printk/printk_safe.c:393
printk+0xba/0xed kernel/printk/printk.c:2070
show_ip+0x22/0x30 arch/x86/kernel/dumpstack.c:124
show_iret_regs+0x10/0x32 arch/x86/kernel/dumpstack.c:131
__show_regs+0x18/0x50 arch/x86/kernel/process_64.c:72
show_trace_log_lvl+0x255/0x2b4 arch/x86/kernel/dumpstack.c:274
show_regs arch/x86/kernel/dumpstack.c:447 [inline]
__die_body arch/x86/kernel/dumpstack.c:393 [inline]
__die+0x51/0x90 arch/x86/kernel/dumpstack.c:407
no_context+0x56b/0x9f0 arch/x86/mm/fault.c:695
__bad_area_nosemaphore+0xa9/0x480 arch/x86/mm/fault.c:789
do_user_addr_fault arch/x86/mm/fault.c:1268 [inline]
handle_page_fault arch/x86/mm/fault.c:1365 [inline]
exc_page_fault+0xc29/0x14c0 arch/x86/mm/fault.c:1418
asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:565
RIP: 0010:__syscall_return_slowpath+0x0/0x280 arch/x86/entry/common.c:309
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
RSP: 0018:ffffc90004cd7f38 EFLAGS: 00010283
RAX: 000000000000000f RBX: 0000000000000002 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff81bc66f2 RDI: ffffc90004cd7f58
RBP: ffffc90004cd7f58 R08: 0000000000000000 R09: ffff8880ae636cdb
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
do_syscall_64+0x6c/0xe0 arch/x86/entry/common.c:368
entry_SYSCALL_64_after_hwframe+0x44/0xa9
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0
Oops: 0002 [#3] PREEMPT SMP KASAN
CPU: 0 PID: 8079 Comm: systemd-udevd Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:in_gate_area_no_mm+0x0/0x6a arch/x86/entry/vsyscall/vsyscall_64.c:343
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
RSP: 0018:ffffc90004cd6988 EFLAGS: 00010093
RAX: 0000000000000000 RBX: ffffc90004cd6a28 RCX: ffffffff8169f800
RDX: ffff888091d90300 RSI: ffffffff8169f82b RDI: 00007f934a4fe840
RBP: 00007f934a4fe840 R08: ffffc90004cd6b38 R09: ffff8880ae623d52
R10: 00007f934a4fe840 R11: 0000000000000001 R12: ffffc90004cd6b38
R13: 0000000000000001 R14: 00007f934a4fe840 R15: ffffc90004cd6a48
FS: 00007f934b3b78c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000008ebc4000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
is_kernel include/linux/kallsyms.h:43 [inline]
is_ksym_addr include/linux/kallsyms.h:49 [inline]
kallsyms_lookup+0xc3/0x2e0 kernel/kallsyms.c:290
__sprint_symbol+0x9c/0x1c0 kernel/kallsyms.c:363
symbol_string+0x14c/0x370 lib/vsprintf.c:969
pointer+0x185/0x970 lib/vsprintf.c:2226
vsnprintf+0x5b2/0x14f0 lib/vsprintf.c:2624
vscnprintf+0x29/0x80 lib/vsprintf.c:2723
printk_safe_log_store+0xf5/0x250 kernel/printk/printk_safe.c:94
vprintk_safe kernel/printk/printk_safe.c:347 [inline]
vprintk_func+0xef/0x1a6 kernel/printk/printk_safe.c:390
printk+0xba/0xed kernel/printk/printk.c:2070
show_ip+0x22/0x30 arch/x86/kernel/dumpstack.c:124
show_iret_regs+0x10/0x32 arch/x86/kernel/dumpstack.c:131
__show_regs+0x18/0x50 arch/x86/kernel/process_64.c:72
show_trace_log_lvl+0x255/0x2b4 arch/x86/kernel/dumpstack.c:274
show_regs arch/x86/kernel/dumpstack.c:447 [inline]
__die_body arch/x86/kernel/dumpstack.c:393 [inline]
__die+0x51/0x90 arch/x86/kernel/dumpstack.c:407
no_context+0x56b/0x9f0 arch/x86/mm/fault.c:695
__bad_area_nosemaphore+0xa9/0x480 arch/x86/mm/fault.c:789
do_user_addr_fault arch/x86/mm/fault.c:1242 [inline]
handle_page_fault arch/x86/mm/fault.c:1365 [inline]
exc_page_fault+0x946/0x14c0 arch/x86/mm/fault.c:1418
asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:565
RIP: 0010:in_gate_area_no_mm+0x0/0x6a arch/x86/entry/vsyscall/vsyscall_64.c:343
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
RSP: 0018:ffffc90004cd7478 EFLAGS: 00010093
RAX: 0000000000000000 RBX: ffffc90004cd7518 RCX: ffffffff8169f800
RDX: ffff888091d90300 RSI: ffffffff8169f82b RDI: 00007f934a4fe840
RBP: 00007f934a4fe840 R08: ffffc90004cd7628 R09: ffffffff8c8c8109
R10: 00007f934a4fe840 R11: 0000000000000000 R12: ffffc90004cd7628
R13: 0000000000000001 R14: 00007f934a4fe840 R15: ffffc90004cd7538
is_kernel include/linux/kallsyms.h:43 [inline]
is_ksym_addr include/linux/kallsyms.h:49 [inline]
kallsyms_lookup+0xc3/0x2e0 kernel/kallsyms.c:290
__sprint_symbol+0x9c/0x1c0 kernel/kallsyms.c:363
symbol_string+0x14c/0x370 lib/vsprintf.c:969
pointer+0x185/0x970 lib/vsprintf.c:2226
vsnprintf+0x5b2/0x14f0 lib/vsprintf.c:2624
vscnprintf+0x29/0x80 lib/vsprintf.c:2723
vprintk_store+0x44/0x4a0 kernel/printk/printk.c:1942
vprintk_emit+0x139/0x770 kernel/printk/printk.c:2003
vprintk_func+0x8f/0x1a6 kernel/printk/printk_safe.c:393
printk+0xba/0xed kernel/printk/printk.c:2070
show_ip+0x22/0x30 arch/x86/kernel/dumpstack.c:124
show_iret_regs+0x10/0x32 arch/x86/kernel/dumpstack.c:131
__show_regs+0x18/0x50 arch/x86/kernel/process_64.c:72
show_trace_log_lvl+0x255/0x2b4 arch/x86/kernel/dumpstack.c:274
show_regs arch/x86/kernel/dumpstack.c:447 [inline]
__die_body arch/x86/kernel/dumpstack.c:393 [inline]
__die+0x51/0x90 arch/x86/kernel/dumpstack.c:407
no_context+0x56b/0x9f0 arch/x86/mm/fault.c:695
__bad_area_nosemaphore+0xa9/0x480 arch/x86/mm/fault.c:789
do_user_addr_fault arch/x86/mm/fault.c:1268 [inline]
handle_page_fault arch/x86/mm/fault.c:1365 [inline]
exc_page_fault+0xc29/0x14c0 arch/x86/mm/fault.c:1418
asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:565
RIP: 0010:__syscall_return_slowpath+0x0/0x280 arch/x86/entry/common.c:309
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 00 00 00 00 00 00 00 00 0
Lost 40 message(s)!


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