Re: [PATCH] mm/swap: consider max pages in iomap_swapfile_add_extent

[Yu Xu <xuyu@linux.alibaba.com>]

On 8/19/21 1:01 AM, Darrick J. Wong wrote:
> On Wed, Aug 18, 2021 at 07:36:51PM +0800, Xu Yu wrote:
>> When the max pages (last_page in the swap header + 1) is smaller than
>> the total pages (inode size) of the swapfile, iomap_swapfile_activate
>> overwrites sis->max with total pages.
>>
>> However, frontswap_map is allocated using max pages, but cleared using
>> sis->max in __frontswap_invalidate_area(). The consequence is that the
>> neighbors of frontswap_map bitmap may be overwritten, and then slab is
>> polluted.
>>
>> This fixes the issue by considering the limitation of max pages of swap
>> info in iomap_swapfile_add_extent().
>>
>> To reproduce the case, compile kernel with slub RED ZONE, then run test:
>> $ sudo stress-ng -a 1 -x softlockup,resources -t 72h --metrics --times \
>>   --verify -v -Y /root/tmpdir/stress-ng/stress-statistic-12.yaml \
>>   --log-file /root/tmpdir/stress-ng/stress-logfile-12.txt \
>>   --temp-path /root/tmpdir/stress-ng/

Hi, Darrick J. Wong,

This is the stress-ng test script from our nightly test, I just copied
as it is.

> 
> 72 hours?  That's not really a targeted reproducer test.

Actually, the system crashes soon, in less than 5 minutes on average.

> 
> Oh, very interesting!  maxpages comes from the swap header.
> 
> # fallocate -l 100m /mnt/a
> # mkswap /mnt/a
> mkswap: /mnt/a: insecure permissions 0644, 0600 suggested.
> Setting up swapspace version 1, size = 100 MiB (104853504 bytes)
> no label, UUID=c6c93d94-3b91-47cc-9684-9c0edbd04759
> # swapon /mnt/a
> swapon: /mnt/a: insecure permissions 0644, 0600 suggested.
> [   68.267848] Adding 102396k swap on /mnt/a.  Priority:-2 extents:1 across:102396k SS
> 
> 
> Ok, ~100M of swap...
> 
> # swapoff /mnt/a
> # fallocate -l 200m /mnt/a
> # swapon /mnt/a
> swapon: /mnt/a: insecure permissions 0644, 0600 suggested.
> [   84.458713] Adding 204796k swap on /mnt/a.  Priority:-2 extents:1 across:204796k SS
> 
> Huh.  200MB of swap, even though we haven't touched the swap header:
> 
> # dd if=/mnt/a bs=4096 count=1 | od -tx1 -Ad -c
> 0000000  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00
>           \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
> *
> 0001024  01  00  00  00  ff  63  00  00  00  00  00  00  66  40  eb  42
>          001  \0  \0  \0 377   c  \0  \0  \0  \0  \0  \0   f   @ 353   B
> 
> Version 1 swap header, 0x63ff pages (~102396kb), 0 bad pages...
> 
> 0001040  8e  81  4e  4e  92  a1  f9  98  d9  43  2f  cc  00  00  00  00
>          216 201   N   N 222 241 371 230 331   C   / 314  \0  \0  \0  \0
> 0001056  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00  00
>           \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
> *
> 0004080  00  00  00  00  00  00  53  57  41  50  53  50  41  43  45  32
>           \0  \0  \0  \0  \0  \0   S   W   A   P   S   P   A   C   E   2
> 0004096
> 
> So yes, iomap_swapfile_* is incorrect.  Even better, we have a targeted
> way to test this now. :)

Yes, this is more straightforward.  I used to focus on the slab
corruption too much.

> 
>> We'll get the error log as below:
>>
>> [ 1151.015141] =============================================================================
>> [ 1151.016489] BUG kmalloc-16 (Not tainted): Right Redzone overwritten
>> [ 1151.017486] -----------------------------------------------------------------------------
>> [ 1151.017486]
>> [ 1151.018997] Disabling lock debugging due to kernel taint
>> [ 1151.019873] INFO: 0x0000000084e43932-0x0000000098d17cae @offset=7392. First byte 0x0 instead of 0xcc
>> [ 1151.021303] INFO: Allocated in __do_sys_swapon+0xcf6/0x1170 age=43417 cpu=9 pid=3816
>> [ 1151.022538]  __slab_alloc+0xe/0x20
>> [ 1151.023069]  __kmalloc_node+0xfd/0x4b0
>> [ 1151.023704]  __do_sys_swapon+0xcf6/0x1170
>> [ 1151.024346]  do_syscall_64+0x33/0x40
>> [ 1151.024925]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> [ 1151.025749] INFO: Freed in put_cred_rcu+0xa1/0xc0 age=43424 cpu=3 pid=2041
>> [ 1151.026889]  kfree+0x276/0x2b0
>> [ 1151.027405]  put_cred_rcu+0xa1/0xc0
>> [ 1151.027949]  rcu_do_batch+0x17d/0x410
>> [ 1151.028566]  rcu_core+0x14e/0x2b0
>> [ 1151.029084]  __do_softirq+0x101/0x29e
>> [ 1151.029645]  asm_call_irq_on_stack+0x12/0x20
>> [ 1151.030381]  do_softirq_own_stack+0x37/0x40
>> [ 1151.031037]  do_softirq.part.15+0x2b/0x30
>> [ 1151.031710]  __local_bh_enable_ip+0x4b/0x50
>> [ 1151.032412]  copy_fpstate_to_sigframe+0x111/0x360
>> [ 1151.033197]  __setup_rt_frame+0xce/0x480
>> [ 1151.033809]  arch_do_signal+0x1a3/0x250
>> [ 1151.034463]  exit_to_user_mode_prepare+0xcf/0x110
>> [ 1151.035242]  syscall_exit_to_user_mode+0x27/0x190
>> [ 1151.035970]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> [ 1151.036795] INFO: Slab 0x000000003b9de4dc objects=44 used=9 fp=0x00000000539e349e flags=0xfffffc0010201
>> [ 1151.038323] INFO: Object 0x000000004855ba01 @offset=7376 fp=0x0000000000000000
>> [ 1151.038323]
>> [ 1151.039683] Redzone  000000008d0afd3d: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc  ................
>> [ 1151.041180] Object   000000004855ba01: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>> [ 1151.042714] Redzone  0000000084e43932: 00 00 00 c0 cc cc cc cc                          ........
>> [ 1151.044120] Padding  000000000864c042: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a  ZZZZZZZZZZZZZZZZ
>> [ 1151.045615] CPU: 5 PID: 3816 Comm: stress-ng Tainted: G    B             5.10.50+ #7
>> [ 1151.046846] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
>> [ 1151.048633] Call Trace:
>> [ 1151.049072]  dump_stack+0x57/0x6a
>> [ 1151.049585]  check_bytes_and_report+0xed/0x110
>> [ 1151.050320]  check_object+0x1eb/0x290
>> [ 1151.050924]  ? __x64_sys_swapoff+0x39a/0x540
>> [ 1151.051646]  free_debug_processing+0x151/0x350
>> [ 1151.052333]  __slab_free+0x21a/0x3a0
>> [ 1151.052938]  ? _cond_resched+0x2d/0x40
>> [ 1151.053529]  ? __vunmap+0x1de/0x220
>> [ 1151.054139]  ? __x64_sys_swapoff+0x39a/0x540
>> [ 1151.054796]  ? kfree+0x276/0x2b0
>> [ 1151.055307]  kfree+0x276/0x2b0
>> [ 1151.055832]  __x64_sys_swapoff+0x39a/0x540
>> [ 1151.056466]  do_syscall_64+0x33/0x40
>> [ 1151.057084]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> [ 1151.057866] RIP: 0033:0x150340b0ffb7
>> [ 1151.058481] Code: Unable to access opcode bytes at RIP 0x150340b0ff8d.
>> [ 1151.059537] RSP: 002b:00007fff7f4ee238 EFLAGS: 00000246 ORIG_RAX: 00000000000000a8
>> [ 1151.060768] RAX: ffffffffffffffda RBX: 00007fff7f4ee66c RCX: 0000150340b0ffb7
>> [ 1151.061904] RDX: 000000000000000a RSI: 0000000000018094 RDI: 00007fff7f4ee860
>> [ 1151.063033] RBP: 00007fff7f4ef980 R08: 0000000000000000 R09: 0000150340a672bd
>> [ 1151.064135] R10: 00007fff7f4edca0 R11: 0000000000000246 R12: 0000000000018094
>> [ 1151.065253] R13: 0000000000000005 R14: 000000000160d930 R15: 00007fff7f4ee66c
>> [ 1151.066413] FIX kmalloc-16: Restoring 0x0000000084e43932-0x0000000098d17cae=0xcc
>> [ 1151.066413]
>> [ 1151.067890] FIX kmalloc-16: Object at 0x000000004855ba01 not freed
>>
>> Fixes: 0e6895ba00b7 ("ext4: implement swap_activate aops using iomap")
>> Signed-off-by: Gang Deng <gavin.dg@linux.alibaba.com>
>> Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
> 
> Looks good; I'll cc you both when I send out the regression test.
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> 
> --D
> 
>> ---
>>   fs/iomap/swapfile.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/fs/iomap/swapfile.c b/fs/iomap/swapfile.c
>> index 6250ca6a1f85..4ecf4e1f68ef 100644
>> --- a/fs/iomap/swapfile.c
>> +++ b/fs/iomap/swapfile.c
>> @@ -31,11 +31,16 @@ static int iomap_swapfile_add_extent(struct iomap_swapfile_info *isi)
>>   {
>>   	struct iomap *iomap = &isi->iomap;
>>   	unsigned long nr_pages;
>> +	unsigned long max_pages;
>>   	uint64_t first_ppage;
>>   	uint64_t first_ppage_reported;
>>   	uint64_t next_ppage;
>>   	int error;
>>   
>> +	if (unlikely(isi->nr_pages >= isi->sis->max))
>> +		return 0;
>> +	max_pages = isi->sis->max - isi->nr_pages;
>> +
>>   	/*
>>   	 * Round the start up and the end down so that the physical
>>   	 * extent aligns to a page boundary.
>> @@ -48,6 +53,7 @@ static int iomap_swapfile_add_extent(struct iomap_swapfile_info *isi)
>>   	if (first_ppage >= next_ppage)
>>   		return 0;
>>   	nr_pages = next_ppage - first_ppage;
>> +	nr_pages = min(nr_pages, max_pages);
>>   
>>   	/*
>>   	 * Calculate how much swap space we're adding; the first page contains
>> -- 
>> 2.20.1.2432.ga663e714
>>

-- 
Thanks,
Yu