[v4] fs: introduce is_dot_or_dotdot helper for cleanup
diff mbox series

Message ID 1575979801-32569-1-git-send-email-yangtiezhu@loongson.cn
State Superseded
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Series
  • [v4] fs: introduce is_dot_or_dotdot helper for cleanup
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Commit Message

Tiezhu Yang Dec. 10, 2019, 12:10 p.m. UTC
There exists many similar and duplicate codes to check "." and "..",
so introduce is_dot_or_dotdot helper to make the code more clean.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---

v4:
  - rename is_dot_dotdot() to is_dot_or_dotdot()

v3:
  - use "name" and "len" as arguments instead of qstr
  - move is_dot_dotdot() to include/linux/namei.h

v2:
  - use the better performance implementation of is_dot_dotdot
  - make it static inline and move it to include/linux/fs.h

 fs/crypto/fname.c     | 16 +++-------------
 fs/ecryptfs/crypto.c  | 10 ----------
 fs/f2fs/f2fs.h        | 11 -----------
 fs/f2fs/hash.c        |  3 ++-
 fs/namei.c            |  6 ++----
 include/linux/namei.h | 10 ++++++++++
 6 files changed, 17 insertions(+), 39 deletions(-)

Comments

Matthew Wilcox Dec. 10, 2019, 12:13 p.m. UTC | #1
On Tue, Dec 10, 2019 at 08:10:01PM +0800, Tiezhu Yang wrote:
> There exists many similar and duplicate codes to check "." and "..",
> so introduce is_dot_or_dotdot helper to make the code more clean.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Eric Biggers Dec. 10, 2019, 7:19 p.m. UTC | #2
On Tue, Dec 10, 2019 at 08:10:01PM +0800, Tiezhu Yang wrote:
> diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
> index 3da3707..ef7eba8 100644
> --- a/fs/crypto/fname.c
> +++ b/fs/crypto/fname.c
> @@ -11,21 +11,11 @@
>   * This has not yet undergone a rigorous security audit.
>   */
>  
> +#include <linux/namei.h>
>  #include <linux/scatterlist.h>
>  #include <crypto/skcipher.h>
>  #include "fscrypt_private.h"
>  
> -static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
> -{
> -	if (str->len == 1 && str->name[0] == '.')
> -		return true;
> -
> -	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
> -		return true;
> -
> -	return false;
> -}
> -
>  /**
>   * fname_encrypt() - encrypt a filename
>   *
> @@ -255,7 +245,7 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
>  	const struct qstr qname = FSTR_TO_QSTR(iname);
>  	struct fscrypt_digested_name digested_name;
>  
> -	if (fscrypt_is_dot_dotdot(&qname)) {
> +	if (is_dot_or_dotdot(qname.name, qname.len)) {

There's no need for the 'qname' variable anymore.  Can you please remove it and
do:

	if (is_dot_or_dotdot(iname->name, iname->len)) {

> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index 7fe7b87..aba114a 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -92,4 +92,14 @@ retry_estale(const long error, const unsigned int flags)
>  	return error == -ESTALE && !(flags & LOOKUP_REVAL);
>  }
>  
> +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 ".".

So I think there needs to either be a len >= 1 check added, *or* you need to
make an argument for why it's okay to not care about the empty name case.

- Eric
Al Viro Dec. 10, 2019, 11:10 p.m. UTC | #3
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 ".".
> 
> So I think there needs to either be a len >= 1 check added, *or* you need to
> make an argument for why it's okay to not care about the empty name case.

Frankly, the only caller that matters in practice is link_path_walk(); _that_
is by far the hottest path that might make use of that thing.

BTW, the callers that might end up passing 0 for len really ought to take
a good look at another thing - that name[0] is, in fact, mapped.  Something
along the lines of
	if (name + len > end_of_buffer)
		sod off
	if (<that function>(name, len))
		....
is not enough, for obvious reasons.
Tiezhu Yang Dec. 11, 2019, 12:56 a.m. UTC | #4
On 12/11/2019 03:19 AM, Eric Biggers wrote:
> On Tue, Dec 10, 2019 at 08:10:01PM +0800, Tiezhu Yang wrote:
>> diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
>> index 3da3707..ef7eba8 100644
>> --- a/fs/crypto/fname.c
>> +++ b/fs/crypto/fname.c
>> @@ -11,21 +11,11 @@
>>    * This has not yet undergone a rigorous security audit.
>>    */
>>   
>> +#include <linux/namei.h>
>>   #include <linux/scatterlist.h>
>>   #include <crypto/skcipher.h>
>>   #include "fscrypt_private.h"
>>   
>> -static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
>> -{
>> -	if (str->len == 1 && str->name[0] == '.')
>> -		return true;
>> -
>> -	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
>> -		return true;
>> -
>> -	return false;
>> -}
>> -
>>   /**
>>    * fname_encrypt() - encrypt a filename
>>    *
>> @@ -255,7 +245,7 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
>>   	const struct qstr qname = FSTR_TO_QSTR(iname);
>>   	struct fscrypt_digested_name digested_name;
>>   
>> -	if (fscrypt_is_dot_dotdot(&qname)) {
>> +	if (is_dot_or_dotdot(qname.name, qname.len)) {
> There's no need for the 'qname' variable anymore.  Can you please remove it and
> do:
>
> 	if (is_dot_or_dotdot(iname->name, iname->len)) {

Hi Eric,

Thanks for your review, I will do it in the v5 patch.

>
>> diff --git a/include/linux/namei.h b/include/linux/namei.h
>> index 7fe7b87..aba114a 100644
>> --- a/include/linux/namei.h
>> +++ b/include/linux/namei.h
>> @@ -92,4 +92,14 @@ retry_estale(const long error, const unsigned int flags)
>>   	return error == -ESTALE && !(flags & LOOKUP_REVAL);
>>   }
>>   
>> +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 ".".
>
> So I think there needs to either be a len >= 1 check added, *or* you need to
> make an argument for why it's okay to not care about the empty name case.

Anyway, let me modify the if condition "len < 2" to "len == 1".

static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
{
         if (unlikely(name[0] == '.')) {
                 if (len == 1 || (len == 2 && name[1] == '.'))
                         return true;
         }

         return false;
}

I will send v5 patch as soon as possible.

Thanks,

Tiezhu Yang

>
> - Eric
Matthew Wilcox Dec. 12, 2019, 6:13 p.m. UTC | #5
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.

Patch
diff mbox series

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 3da3707..ef7eba8 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -11,21 +11,11 @@ 
  * This has not yet undergone a rigorous security audit.
  */
 
+#include <linux/namei.h>
 #include <linux/scatterlist.h>
 #include <crypto/skcipher.h>
 #include "fscrypt_private.h"
 
-static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
-{
-	if (str->len == 1 && str->name[0] == '.')
-		return true;
-
-	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
-		return true;
-
-	return false;
-}
-
 /**
  * fname_encrypt() - encrypt a filename
  *
@@ -255,7 +245,7 @@  int fscrypt_fname_disk_to_usr(struct inode *inode,
 	const struct qstr qname = FSTR_TO_QSTR(iname);
 	struct fscrypt_digested_name digested_name;
 
-	if (fscrypt_is_dot_dotdot(&qname)) {
+	if (is_dot_or_dotdot(qname.name, qname.len)) {
 		oname->name[0] = '.';
 		oname->name[iname->len - 1] = '.';
 		oname->len = iname->len;
@@ -323,7 +313,7 @@  int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
 	memset(fname, 0, sizeof(struct fscrypt_name));
 	fname->usr_fname = iname;
 
-	if (!IS_ENCRYPTED(dir) || fscrypt_is_dot_dotdot(iname)) {
+	if (!IS_ENCRYPTED(dir) || is_dot_or_dotdot(iname->name, iname->len)) {
 		fname->disk_name.name = (unsigned char *)iname->name;
 		fname->disk_name.len = iname->len;
 		return 0;
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index f91db24..2014f8f 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1991,16 +1991,6 @@  int ecryptfs_encrypt_and_encode_filename(
 	return rc;
 }
 
-static bool is_dot_dotdot(const char *name, size_t name_size)
-{
-	if (name_size == 1 && name[0] == '.')
-		return true;
-	else if (name_size == 2 && name[0] == '.' && name[1] == '.')
-		return true;
-
-	return false;
-}
-
 /**
  * ecryptfs_decode_and_decrypt_filename - converts the encoded cipher text name to decoded plaintext
  * @plaintext_name: The plaintext name
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 5a888a0..3d5e684 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2767,17 +2767,6 @@  static inline bool f2fs_cp_error(struct f2fs_sb_info *sbi)
 	return is_set_ckpt_flags(sbi, CP_ERROR_FLAG);
 }
 
-static inline bool is_dot_dotdot(const struct qstr *str)
-{
-	if (str->len == 1 && str->name[0] == '.')
-		return true;
-
-	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
-		return true;
-
-	return false;
-}
-
 static inline bool f2fs_may_extent_tree(struct inode *inode)
 {
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
diff --git a/fs/f2fs/hash.c b/fs/f2fs/hash.c
index 5bc4dcd..ef155c2 100644
--- a/fs/f2fs/hash.c
+++ b/fs/f2fs/hash.c
@@ -15,6 +15,7 @@ 
 #include <linux/cryptohash.h>
 #include <linux/pagemap.h>
 #include <linux/unicode.h>
+#include <linux/namei.h>
 
 #include "f2fs.h"
 
@@ -82,7 +83,7 @@  static f2fs_hash_t __f2fs_dentry_hash(const struct qstr *name_info,
 	if (fname && !fname->disk_name.name)
 		return cpu_to_le32(fname->hash);
 
-	if (is_dot_dotdot(name_info))
+	if (is_dot_or_dotdot(name, len))
 		return 0;
 
 	/* Initialize the default seed for the hash checksum functions */
diff --git a/fs/namei.c b/fs/namei.c
index d6c91d1..f3a4439 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2451,10 +2451,8 @@  static int lookup_one_len_common(const char *name, struct dentry *base,
 	if (!len)
 		return -EACCES;
 
-	if (unlikely(name[0] == '.')) {
-		if (len < 2 || (len == 2 && name[1] == '.'))
-			return -EACCES;
-	}
+	if (is_dot_or_dotdot(name, len))
+		return -EACCES;
 
 	while (len--) {
 		unsigned int c = *(const unsigned char *)name++;
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 7fe7b87..aba114a 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -92,4 +92,14 @@  retry_estale(const long error, const unsigned int flags)
 	return error == -ESTALE && !(flags & LOOKUP_REVAL);
 }
 
+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;
+}
+
 #endif /* _LINUX_NAMEI_H */