Messages in this thread | | | Date | Wed, 17 Jul 2013 05:20:31 +0100 | Subject | Re: [patch] Squashfs: sanity check information from disk | From | Phillip Lougher <> |
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On 15 July 2013 17:17, Dan Carpenter <dan.carpenter@oracle.com> wrote: > We read the size of the name from the disk, but a larger name than > expected would cause memory corruption.
Thanks for the patch, it's queued for the next merge window. There's one mistake with the patch, but I can fix it when it's applied, or you can send a revised patch (see later).
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> > --- > I don't know this code very well, but to me it looks like there is an > off by one bug here as well.
No, the code is perfectly OK here, the confusion stems from what the +1 is doing.
> > We say: > > size = le32_to_cpu(index->size) + 1; > > The "+ 1" is presumably for the NUL terminator. Then we do:
index->size is one less than the size of the name, so to get the true size of the name we must add one to it. If index->size is 7 it means the size of the name stored on disk is 8 bytes.
This storing the size as one less came from the observation we never have 0 length filenames, and so 0 would effectively never be used.
> > index->name[size] = '\0'; > > That means we are putting a NUL character one space beyond the end of > the array. Presumably the first character of the next thing saved to > the disk is usually zero so that's why we don't notice that we are > reading a extra character when we read "size" number of bytes.
> > diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c > index 7834a51..bc1334c 100644 > --- a/fs/squashfs/namei.c > +++ b/fs/squashfs/namei.c > @@ -79,7 +79,8 @@ static int get_dir_index_using_name(struct super_block *sb, > int len) > { > struct squashfs_sb_info *msblk = sb->s_fs_info; > - int i, size, length = 0, err; > + int i, length = 0, err; > + unsigned int size; > struct squashfs_dir_index *index; > char *str; > > @@ -103,6 +104,10 @@ static int get_dir_index_using_name(struct super_block *sb, > > > size = le32_to_cpu(index->size) + 1; > + if (size >= SQUASHFS_NAME_LEN + 1) {
This should be
if (size > SQUASHFS_NAME_LEN)
I can fix it, or you can send a revised patch.
Phillip
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