linux-kernel - Re: [PATCH] jffs2: correct logic when creating a hole in jffs2_write_begin

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Message-ID: <MN2PR17MB33753129D81B1E42A54768BDB8949@MN2PR17MB3375.namprd17.prod.outlook.com>
Date:   Tue, 26 Jul 2022 00:11:49 +0000
From:   Vanessa Page <Vebpe@...look.com>
To:     Yifei Liu <yifeliu@...stonybrook.edu>
CC:     "ezk@...stonybrook.edu" <ezk@...stonybrook.edu>,
        "madkar@...stonybrook.edu" <madkar@...stonybrook.edu>,
        David Woodhouse <dwmw2@...radead.org>,
        Richard Weinberger <richard@....at>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Kyeong Yoo <kyeong.yoo@...iedtelesis.co.nz>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] jffs2: correct logic when creating a hole in
 jffs2_write_begin

Stop fucking emailing me you suck fuck. You want a password so you can hack my shit you broke motherfucker

People are not THAT stupid. 

> On Jul 25, 2022, at 6:11 PM, Vanessa Page <Vebpe@...look.com> wrote:
> 
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> 
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> 
>> On Jul 25, 2022, at 1:04 AM, Vanessa Page <Vebpe@...look.com> wrote:
>> 
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>> 
>> Sent from my iPhon✌️
>> 
>>>> On Jul 25, 2022, at 1:01 AM, Yifei Liu <yifeliu@...stonybrook.edu> wrote:
>>> 
>>> Bug description and fix:
>>> 
>>> 1. Write data to a file, say all 1s from offset 0 to 16.
>>> 
>>> 2. Truncate the file to a smaller size, say 8 bytes.
>>> 
>>> 3. Write new bytes (say 2s) from an offset past the original size of the
>>> file, say at offset 20, for 4 bytes.  This is supposed to create a "hole"
>>> in the file, meaning that the bytes from offset 8 (where it was truncated
>>> above) up to the new write at offset 20, should all be 0s (zeros).
>>> 
>>> 4. flush all caches using "echo 3 > /proc/sys/vm/drop_caches" (or unmount
>>> and remount) the f/s.
>>> 
>>> 5. Check the content of the file.  It is wrong.  The 1s that used to be
>>> between bytes 9 and 16, before the truncation, have REAPPEARED (they should
>>> be 0s).
>>> 
>>> We wrote a script and helper C program to reproduce the bug
>>> (reproduce_jffs2_write_begin_issue.sh, write_file.c, and Makefile).  We can
>>> make them available to anyone.
>>> 
>>> The above example is shown when writing a small file within the same first
>>> page.  But the bug happens for larger files, as long as steps 1, 2, and 3
>>> above all happen within the same page.
>>> 
>>> The problem was traced to the jffs2_write_begin code, where it goes into an
>>> 'if' statement intended to handle writes past the current EOF (i.e., writes
>>> that may create a hole).  The code computes a 'pageofs' that is the floor
>>> of the write position (pos), aligned to the page size boundary.  In other
>>> words, 'pageofs' will never be larger than 'pos'.  The code then sets the
>>> internal jffs2_raw_inode->isize to the size of max(current inode size,
>>> pageofs) but that is wrong: the new file size should be the 'pos', which is
>>> larger than both the current inode size and pageofs.
>>> 
>>> Similarly, the code incorrectly sets the internal jffs2_raw_inode->dsize to
>>> the difference between the pageofs minus current inode size; instead it
>>> should be the current pos minus the current inode size.  Finally,
>>> inode->i_size was also set incorrectly.
>>> 
>>> The patch below fixes this bug.  The bug was discovered using a new tool
>>> for finding f/s bugs using model checking, called MCFS (Model Checking File
>>> Systems).
>>> 
>>> Signed-off-by: Yifei Liu <yifeliu@...stonybrook.edu>
>>> Signed-off-by: Erez Zadok <ezk@...stonybrook.edu>
>>> Signed-off-by: Manish Adkar <madkar@...stonybrook.edu>
>>> ---
>>> fs/jffs2/file.c | 15 +++++++--------
>>> 1 file changed, 7 insertions(+), 8 deletions(-)
>>> 
>>> diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
>>> index ba86acbe12d3..0479096b96e4 100644
>>> --- a/fs/jffs2/file.c
>>> +++ b/fs/jffs2/file.c
>>> @@ -137,19 +137,18 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
>>>  struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
>>>  struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
>>>  pgoff_t index = pos >> PAGE_SHIFT;
>>> -    uint32_t pageofs = index << PAGE_SHIFT;
>>>  int ret = 0;
>>> 
>>>  jffs2_dbg(1, "%s()\n", __func__);
>>> 
>>> -    if (pageofs > inode->i_size) {
>>> -        /* Make new hole frag from old EOF to new page */
>>> +    if (pos > inode->i_size) {
>>> +        /* Make new hole frag from old EOF to new position */
>>>      struct jffs2_raw_inode ri;
>>>      struct jffs2_full_dnode *fn;
>>>      uint32_t alloc_len;
>>> 
>>> -        jffs2_dbg(1, "Writing new hole frag 0x%x-0x%x between current EOF and new page\n",
>>> -              (unsigned int)inode->i_size, pageofs);
>>> +        jffs2_dbg(1, "Writing new hole frag 0x%x-0x%x between current EOF and new position\n",
>>> +              (unsigned int)inode->i_size, (uint32_t)pos);
>>> 
>>>      ret = jffs2_reserve_space(c, sizeof(ri), &alloc_len,
>>>                    ALLOC_NORMAL, JFFS2_SUMMARY_INODE_SIZE);
>>> @@ -169,10 +168,10 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
>>>      ri.mode = cpu_to_jemode(inode->i_mode);
>>>      ri.uid = cpu_to_je16(i_uid_read(inode));
>>>      ri.gid = cpu_to_je16(i_gid_read(inode));
>>> -        ri.isize = cpu_to_je32(max((uint32_t)inode->i_size, pageofs));
>>> +        ri.isize = cpu_to_je32((uint32_t)pos);
>>>      ri.atime = ri.ctime = ri.mtime = cpu_to_je32(JFFS2_NOW());
>>>      ri.offset = cpu_to_je32(inode->i_size);
>>> -        ri.dsize = cpu_to_je32(pageofs - inode->i_size);
>>> +        ri.dsize = cpu_to_je32((uint32_t)pos - inode->i_size);
>>>      ri.csize = cpu_to_je32(0);
>>>      ri.compr = JFFS2_COMPR_ZERO;
>>>      ri.node_crc = cpu_to_je32(crc32(0, &ri, sizeof(ri)-8));
>>> @@ -202,7 +201,7 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
>>>          goto out_err;
>>>      }
>>>      jffs2_complete_reservation(c);
>>> -        inode->i_size = pageofs;
>>> +        inode->i_size = pos;
>>>      mutex_unlock(&f->sem);
>>>  }
>>> 
>>> -- 
>>> 2.25.1
>>> 
>>> 
>>> ______________________________________________________
>>> Linux MTD discussion mailing list
>>> http://lists.infradead.org/mailman/listinfo/linux-mtd/

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