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Subject: Re: [PATCH V2] proc: fix ubsan warning in mem_lseek
From:   yangerkun <yangerkun@huawei.com>
To:     <viro@zeniv.linux.org.uk>, <adobriyan@gmail.com>
CC:     <linux-fsdevel@vger.kernel.org>, <zhengbin13@huawei.com>,
        <yi.zhang@huawei.com>, <houtao1@huawei.com>
References: <20190902065706.60754-1-yangerkun@huawei.com>
 <7452f3d2-1fcf-2627-cbee-b9a920c17fcb@huawei.com>
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Date:   Tue, 17 Sep 2019 14:09:38 +0800
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Ping again...

On 2019/9/6 13:48, yangerkun wrote:
> Ping.
>
> On 2019/9/2 14:57, yangerkun wrote:
>> UBSAN has reported a overflow with mem_lseek. And it's fine with
>> mem_open set file mode with FMODE_UNSIGNED_OFFSET(memory_lseek).
>> However, another file use mem_lseek do lseek can have not
>> FMODE_UNSIGNED_OFFSET(proc_kpagecount_operations/proc_pagemap_operations), 
>>
>> fix it by checking overflow and FMODE_UNSIGNED_OFFSET.
>>
>> ==================================================================
>> UBSAN: Undefined behaviour in ../fs/proc/base.c:941:15
>> signed integer overflow:
>> 4611686018427387904 + 4611686018427387904 cannot be represented in 
>> type 'long long int'
>> CPU: 4 PID: 4762 Comm: syz-executor.1 Not tainted 4.4.189 #3
>> Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
>> Call trace:
>> [<ffffff90080a5f28>] dump_backtrace+0x0/0x590 
>> arch/arm64/kernel/traps.c:91
>> [<ffffff90080a64f0>] show_stack+0x38/0x60 arch/arm64/kernel/traps.c:234
>> [<ffffff9008986a34>] __dump_stack lib/dump_stack.c:15 [inline]
>> [<ffffff9008986a34>] dump_stack+0x128/0x184 lib/dump_stack.c:51
>> [<ffffff9008a2d120>] ubsan_epilogue+0x34/0x9c lib/ubsan.c:166
>> [<ffffff9008a2d8b8>] handle_overflow+0x228/0x280 lib/ubsan.c:197
>> [<ffffff9008a2da2c>] __ubsan_handle_add_overflow+0x4c/0x68 
>> lib/ubsan.c:204
>> [<ffffff900862b9f4>] mem_lseek+0x12c/0x130 fs/proc/base.c:941
>> [<ffffff90084ef78c>] vfs_llseek fs/read_write.c:260 [inline]
>> [<ffffff90084ef78c>] SYSC_lseek fs/read_write.c:285 [inline]
>> [<ffffff90084ef78c>] SyS_lseek+0x164/0x1f0 fs/read_write.c:276
>> [<ffffff9008093c80>] el0_svc_naked+0x30/0x34
>> ==================================================================
>>
>> Signed-off-by: yangerkun <yangerkun@huawei.com>
>> ---
>>   fs/proc/base.c     | 32 ++++++++++++++++++++++++--------
>>   fs/read_write.c    |  5 -----
>>   include/linux/fs.h |  5 +++++
>>   3 files changed, 29 insertions(+), 13 deletions(-)
>>
>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>> index ebea950..a6c701b 100644
>> --- a/fs/proc/base.c
>> +++ b/fs/proc/base.c
>> @@ -882,18 +882,34 @@ static ssize_t mem_write(struct file *file, 
>> const char __user *buf,
>>     loff_t mem_lseek(struct file *file, loff_t offset, int orig)
>>   {
>> +    loff_t ret = 0;
>> +
>> +    spin_lock(&file->f_lock);
>>       switch (orig) {
>> -    case 0:
>> -        file->f_pos = offset;
>> -        break;
>> -    case 1:
>> -        file->f_pos += offset;
>> +    case SEEK_CUR:
>> +        offset += file->f_pos;
>> +        /* fall through */
>> +    case SEEK_SET:
>> +        /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
>> +        if ((unsigned long long)offset >= -MAX_ERRNO)
>> +            ret = -EOVERFLOW;
>>           break;
>>       default:
>> -        return -EINVAL;
>> +        ret = -EINVAL;
>> +    }
>> +
>> +    if (!ret) {
>> +        if (offset < 0 && !(unsigned_offsets(file))) {
>> +            ret = -EINVAL;
>> +        } else {
>> +            file->f_pos = offset;
>> +            ret = file->f_pos;
>> +            force_successful_syscall_return();
>> +        }
>>       }
>> -    force_successful_syscall_return();
>> -    return file->f_pos;
>> +
>> +    spin_unlock(&file->f_lock);
>> +    return ret;
>>   }
>>     static int mem_release(struct inode *inode, struct file *file)
>> diff --git a/fs/read_write.c b/fs/read_write.c
>> index 5bbf587..961966e 100644
>> --- a/fs/read_write.c
>> +++ b/fs/read_write.c
>> @@ -34,11 +34,6 @@ const struct file_operations generic_ro_fops = {
>>     EXPORT_SYMBOL(generic_ro_fops);
>>   -static inline bool unsigned_offsets(struct file *file)
>> -{
>> -    return file->f_mode & FMODE_UNSIGNED_OFFSET;
>> -}
>> -
>>   /**
>>    * vfs_setpos - update the file offset for lseek
>>    * @file:    file structure in question
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 997a530..e5edbc9 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -3074,6 +3074,11 @@ extern void
>>   file_ra_state_init(struct file_ra_state *ra, struct address_space 
>> *mapping);
>>   extern loff_t noop_llseek(struct file *file, loff_t offset, int 
>> whence);
>>   extern loff_t no_llseek(struct file *file, loff_t offset, int whence);
>> +static inline bool unsigned_offsets(struct file *file)
>> +{
>> +    return file->f_mode & FMODE_UNSIGNED_OFFSET;
>> +}
>> +
>>   extern loff_t vfs_setpos(struct file *file, loff_t offset, loff_t 
>> maxsize);
>>   extern loff_t generic_file_llseek(struct file *file, loff_t offset, 
>> int whence);
>>   extern loff_t generic_file_llseek_size(struct file *file, loff_t 
>> offset,