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exfat: fix the new buffer was not zeroed before writing

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In exfat, not only the newly allocated space will be mapped as
the new buffer, but also the space between ->valid_size and the
file size will be mapped as the new buffer. If the buffer is
mapped as new in ->write_begin(), it will be zeroed. But if the
buffer has been mapped as new before ->write_begin(), ->write_begin()
will not zero them, resulting in access to uninitialized data.

So this commit uses folio_zero_new_buffers() to zero the new buffers
after ->write_begin().

Fixes: 6630ea49103c ("exfat: move extend valid_size into ->page_mkwrite()")
Reported-by: syzbot+91ae49e1c1a2634d20c0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=91ae49e1c1a2634d20c0
Tested-by: syzbot+91ae49e1c1a2634d20c0@syzkaller.appspotmail.com
Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
Yuezhang Mo 2024-12-12 16:29:23 +08:00 committed by Namjae Jeon
parent 4265319f10
commit d141e72aef
1 changed files with 6 additions and 0 deletions
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6
fs/exfat/file.c
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@ -545,6 +545,7 @@ static int exfat_extend_valid_size(struct file *file, loff_t new_valid_size)
while (pos < new_valid_size) {
u32 len;
struct folio *folio;
unsigned long off;
len = PAGE_SIZE - (pos & (PAGE_SIZE - 1));
if (pos + len > new_valid_size)
@ -554,6 +555,9 @@ static int exfat_extend_valid_size(struct file *file, loff_t new_valid_size)
if (err)
goto out;
off = offset_in_folio(folio, pos);
folio_zero_new_buffers(folio, off, off + len);
err = ops->write_end(file, mapping, pos, len, len, folio, NULL);
if (err < 0)
goto out;
@ -563,6 +567,8 @@ static int exfat_extend_valid_size(struct file *file, loff_t new_valid_size)
cond_resched();
}
return 0;
out:
return err;
}