* [willy@infradead.org: Re: [willy@infradead.org: Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup]]
@ 2020-01-28 22:11 Matthew Wilcox
2020-01-29 1:23 ` [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup Andreas Dilger
0 siblings, 1 reply; 3+ messages in thread
From: Matthew Wilcox @ 2020-01-28 22:11 UTC (permalink / raw)
To: linux-ext4, Andreas Dilger
I've tried to get Ted's opinion on this a few times with radio silence.
Or email is broken. Anyone else care to offer an opinion?
----- Forwarded message from Matthew Wilcox <willy@infradead.org> -----
Date: Thu, 23 Jan 2020 21:11:43 -0800
From: Matthew Wilcox <willy@infradead.org>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Subject: Re: [willy@infradead.org: Re: [PATCH v4] fs: introduce
is_dot_or_dotdot helper for cleanup]
ping?
On Mon, Dec 30, 2019 at 06:13:03AM -0800, Matthew Wilcox wrote:
>
> Didn't see a response from you on this. Can you confirm the three
> cases in ext4 mentioned below should be converted to return -EUNCLEAN?
>
> ----- Forwarded message from Matthew Wilcox <willy@infradead.org> -----
>
> Date: Thu, 12 Dec 2019 10:13:02 -0800
> From: Matthew Wilcox <willy@infradead.org>
> To: Eric Biggers <ebiggers@kernel.org>
> Cc: Tiezhu Yang <yangtiezhu@loongson.cn>, Alexander Viro
> <viro@zeniv.linux.org.uk>, "Theodore Y. Ts'o" <tytso@mit.edu>, Jaegeuk
> Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>, Tyler Hicks
> <tyhicks@canonical.com>, linux-fsdevel@vger.kernel.org,
> ecryptfs@vger.kernel.org, linux-fscrypt@vger.kernel.org,
> linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup
> User-Agent: Mutt/1.12.1 (2019-06-15)
>
> On Tue, Dec 10, 2019 at 11:19:13AM -0800, Eric Biggers wrote:
> > > +static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
> > > +{
> > > + if (unlikely(name[0] == '.')) {
> > > + if (len < 2 || (len == 2 && name[1] == '.'))
> > > + return true;
> > > + }
> > > +
> > > + return false;
> > > +}
> >
> > This doesn't handle the len=0 case. Did you check that none of the users pass
> > in zero-length names? It looks like fscrypt_fname_disk_to_usr() can, if the
> > directory entry on-disk has a zero-length name. Currently it will return
> > -EUCLEAN in that case, but with this patch it may think it's the name ".".
>
> Trying to wrench this back on track ...
>
> fscrypt_fname_disk_to_usr is called by:
>
> fscrypt_get_symlink():
> if (cstr.len == 0)
> return ERR_PTR(-EUCLEAN);
> ext4_readdir():
> Does not currently check de->name_len. I believe this check should
> be added to __ext4_check_dir_entry() because a zero-length directory
> entry can affect both encrypted and non-encrypted directory entries.
> dx_show_leaf():
> Same as ext4_readdir(). Should probably call ext4_check_dir_entry()?
> htree_dirblock_to_tree():
> Would be covered by a fix to ext4_check_dir_entry().
> f2fs_fill_dentries():
> if (de->name_len == 0) {
> ...
> ubifs_readdir():
> Does not currently check de->name_len. Also affects non-encrypted
> directory entries.
>
> So of the six callers, two of them already check the dirent length for
> being zero, and four of them ought to anyway, but don't. I think they
> should be fixed, but clearly we don't historically check for this kind
> of data corruption (strangely), so I don't think that's a reason to hold
> up this patch until the individual filesystems are fixed.
>
> ----- End forwarded message -----
----- End forwarded message -----
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup
2020-01-28 22:11 [willy@infradead.org: Re: [willy@infradead.org: Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup]] Matthew Wilcox
@ 2020-01-29 1:23 ` Andreas Dilger
2020-01-29 7:36 ` Matthew Wilcox
0 siblings, 1 reply; 3+ messages in thread
From: Andreas Dilger @ 2020-01-29 1:23 UTC (permalink / raw)
To: Matthew Wilcox
Cc: linux-ext4, Tiezhu Yang, Theodore Y. Ts'o, Chao Yu,
linux-fscrypt, linux-fsdevel
[-- Attachment #1: Type: text/plain, Size: 4261 bytes --]
On Jan 28, 2020, at 3:11 PM, Matthew Wilcox <willy@infradead.org> wrote:
>
>
> I've tried to get Ted's opinion on this a few times with radio silence.
> Or email is broken. Anyone else care to offer an opinion?
Maybe I'm missing something, but I think the discussion of the len == 0
case is now moot, since PATCH v6 (which is the latest version that I can
find) is checking for "len >= 1" before accessing name[0]:
+static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
+{
+ if (len >= 1 && unlikely(name[0] == '.')) {
+ if (len == 1 || (len == 2 && name[1] == '.'))
+ return true;
+ }
+
+ return false;
+}
This seems a tiny bit sub-optimal, as (len >= 1) is true for almost every
filename, so it doesn't allow failing the condition quickly. Checking
for exactly (len == 1) and (len == 2) allows failing this condition for
most of the files immediately, which makes "unlikely()" actually useful,
and allows simplifying the inside condition.
static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
{
if (unlikely((len == 1 || len == 2) && name[0] == '.')) {
if (len == 1 || name[1] == '.')
return true;
}
return false;
}
That said, this is at best micro-optimization so it isn't obvious this is
much of an improvement or not.
Cheers, Andreas
> On Mon, Dec 30, 2019 at 06:13:03AM -0800, Matthew Wilcox wrote:
>>
>> Didn't see a response from you on this. Can you confirm the three
>> cases in ext4 mentioned below should be converted to return -EUNCLEAN?
>>
>> ----- Forwarded message from Matthew Wilcox <willy@infradead.org> -----
>>
>> Date: Thu, 12 Dec 2019 10:13:02 -0800
>> From: Matthew Wilcox <willy@infradead.org>
>> To: Eric Biggers <ebiggers@kernel.org>
>> Cc: Tiezhu Yang <yangtiezhu@loongson.cn>, Alexander Viro
>> <viro@zeniv.linux.org.uk>, "Theodore Y. Ts'o" <tytso@mit.edu>, Jaegeuk
>> Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>, Tyler Hicks
>> <tyhicks@canonical.com>, linux-fsdevel@vger.kernel.org,
>> ecryptfs@vger.kernel.org, linux-fscrypt@vger.kernel.org,
>> linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
>> Subject: Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup
>> User-Agent: Mutt/1.12.1 (2019-06-15)
>>
>> On Tue, Dec 10, 2019 at 11:19:13AM -0800, Eric Biggers wrote:
>>>> +static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
>>>> +{
>>>> + if (unlikely(name[0] == '.')) {
>>>> + if (len < 2 || (len == 2 && name[1] == '.'))
>>>> + return true;
>>>> + }
>>>> +
>>>> + return false;
>>>> +}
>>>
>>> This doesn't handle the len=0 case. Did you check that none of the users pass
>>> in zero-length names? It looks like fscrypt_fname_disk_to_usr() can, if the
>>> directory entry on-disk has a zero-length name. Currently it will return
>>> -EUCLEAN in that case, but with this patch it may think it's the name ".".
>>
>> Trying to wrench this back on track ...
>>
>> fscrypt_fname_disk_to_usr is called by:
>>
>> fscrypt_get_symlink():
>> if (cstr.len == 0)
>> return ERR_PTR(-EUCLEAN);
>> ext4_readdir():
>> Does not currently check de->name_len. I believe this check should
>> be added to __ext4_check_dir_entry() because a zero-length directory
>> entry can affect both encrypted and non-encrypted directory entries.
>> dx_show_leaf():
>> Same as ext4_readdir(). Should probably call ext4_check_dir_entry()?
>> htree_dirblock_to_tree():
>> Would be covered by a fix to ext4_check_dir_entry().
>> f2fs_fill_dentries():
>> if (de->name_len == 0) {
>> ...
>> ubifs_readdir():
>> Does not currently check de->name_len. Also affects non-encrypted
>> directory entries.
>>
>> So of the six callers, two of them already check the dirent length for
>> being zero, and four of them ought to anyway, but don't. I think they
>> should be fixed, but clearly we don't historically check for this kind
>> of data corruption (strangely), so I don't think that's a reason to hold
>> up this patch until the individual filesystems are fixed.
>>
>> ----- End forwarded message -----
>
> ----- End forwarded message -----
Cheers, Andreas
[-- Attachment #2: Message signed with OpenPGP --]
[-- Type: application/pgp-signature, Size: 873 bytes --]
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup
2020-01-29 1:23 ` [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup Andreas Dilger
@ 2020-01-29 7:36 ` Matthew Wilcox
0 siblings, 0 replies; 3+ messages in thread
From: Matthew Wilcox @ 2020-01-29 7:36 UTC (permalink / raw)
To: Andreas Dilger
Cc: linux-ext4, Tiezhu Yang, Theodore Y. Ts'o, Chao Yu,
linux-fscrypt, linux-fsdevel
On Tue, Jan 28, 2020 at 06:23:18PM -0700, Andreas Dilger wrote:
> On Jan 28, 2020, at 3:11 PM, Matthew Wilcox <willy@infradead.org> wrote:
> > I've tried to get Ted's opinion on this a few times with radio silence.
> > Or email is broken. Anyone else care to offer an opinion?
>
> Maybe I'm missing something, but I think the discussion of the len == 0
> case is now moot, since PATCH v6 (which is the latest version that I can
> find) is checking for "len >= 1" before accessing name[0]:
Regardless of _this_ patch, the question is "Should ext4 be checking
for filenames of zero length and reporting -EUCLEAN if it finds any?"
I believe the answer is yes, since it's clearly a corrupted filesystem,
but I may be missing something.
Thanks for your reply.
> >> fscrypt_get_symlink():
> >> if (cstr.len == 0)
> >> return ERR_PTR(-EUCLEAN);
> >> ext4_readdir():
> >> Does not currently check de->name_len. I believe this check should
> >> be added to __ext4_check_dir_entry() because a zero-length directory
> >> entry can affect both encrypted and non-encrypted directory entries.
> >> dx_show_leaf():
> >> Same as ext4_readdir(). Should probably call ext4_check_dir_entry()?
> >> htree_dirblock_to_tree():
> >> Would be covered by a fix to ext4_check_dir_entry().
> >> f2fs_fill_dentries():
> >> if (de->name_len == 0) {
> >> ...
> >> ubifs_readdir():
> >> Does not currently check de->name_len. Also affects non-encrypted
> >> directory entries.
> >>
> >> So of the six callers, two of them already check the dirent length for
> >> being zero, and four of them ought to anyway, but don't. I think they
> >> should be fixed, but clearly we don't historically check for this kind
> >> of data corruption (strangely), so I don't think that's a reason to hold
> >> up this patch until the individual filesystems are fixed.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-01-29 7:36 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-01-28 22:11 [willy@infradead.org: Re: [willy@infradead.org: Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup]] Matthew Wilcox
2020-01-29 1:23 ` [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup Andreas Dilger
2020-01-29 7:36 ` Matthew Wilcox
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).