[PATCH v5 0/2] fix the fallback implementation of get_name

[PATCH v5 0/2] fix the fallback implementation of get_name

[Chuck Lever]

Last call.

Topic branch for fs/exportfs:

https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git
branch: exportfs-next

Changes since v4:
- Make it easier to backport 1/2
- Replace "len < 2" with "len == 1" for clarity

Changes since v3:
- is_dot_dotdot() now checks that the file name length > 0

Changes since v2:
- Capture the open-coded "is_dot_dotdot" implementation in
 lookup_one_common()

Changes since v1:
- Fixes: was dropped from 1/2
- Added a patch to hoist is_dot_dotdot() into linux/fs.h

---

Chuck Lever (1):
      fs: Create a generic is_dot_dotdot() utility

Trond Myklebust (1):
      exportfs: fix the fallback implementation of the get_name export operation


 fs/crypto/fname.c    |  8 +-------
 fs/ecryptfs/crypto.c | 10 ----------
 fs/exportfs/expfs.c  |  2 +-
 fs/f2fs/f2fs.h       | 11 -----------
 fs/namei.c           |  6 ++----
 include/linux/fs.h   | 11 +++++++++++
 6 files changed, 15 insertions(+), 33 deletions(-)

--
Chuck Lever

[PATCH v5 1/2] exportfs: fix the fallback implementation of the get_name export operation

[Chuck Lever]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

The fallback implementation for the get_name export operation uses
readdir() to try to match the inode number to a filename. That filename
is then used together with lookup_one() to produce a dentry.
A problem arises when we match the '.' or '..' entries, since that
causes lookup_one() to fail. This has sometimes been seen to occur for
filesystems that violate POSIX requirements around uniqueness of inode
numbers, something that is common for snapshot directories.

This patch just ensures that we skip '.' and '..' rather than allowing a
match.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/linux-nfs/CAOQ4uxiOZobN76OKB-VBNXWeFKVwLW_eK5QtthGyYzWU9mjb7Q@mail.gmail.com/
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/exportfs/expfs.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 3ae0154c5680..dcf7d86c2ce4 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -244,6 +244,16 @@ struct getdents_callback {
 	int sequence;		/* sequence counter */
 };
 
+/* Copied from lookup_one_common() */
+static inline bool is_dot_dotdot(const char *name, size_t len)
+{
+	if (unlikely(name[0] == '.')) {
+		if (len < 2 || (len == 2 && name[1] == '.'))
+			return true;
+	}
+	return false;
+}
+
 /*
  * A rather strange filldir function to capture
  * the name matching the specified inode number.
@@ -255,7 +265,7 @@ static bool filldir_one(struct dir_context *ctx, const char *name, int len,
 		container_of(ctx, struct getdents_callback, ctx);
 
 	buf->sequence++;
-	if (buf->ino == ino && len <= NAME_MAX) {
+	if (buf->ino == ino && len <= NAME_MAX && !is_dot_dotdot(name, len)) {
 		memcpy(buf->name, name, len);
 		buf->name[len] = '\0';
 		buf->found = 1;

[PATCH v5 2/2] fs: Create a generic is_dot_dotdot() utility

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

De-duplicate the same functionality in several places by hoisting
the is_dot_dotdot() utility function into linux/fs.h.

Suggested-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/crypto/fname.c    |    8 +-------
 fs/ecryptfs/crypto.c |   10 ----------
 fs/exportfs/expfs.c  |   10 ----------
 fs/f2fs/f2fs.h       |   11 -----------
 fs/namei.c           |    6 ++----
 include/linux/fs.h   |   11 +++++++++++
 6 files changed, 14 insertions(+), 42 deletions(-)

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 7b3fc189593a..0ad52fbe51c9 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -74,13 +74,7 @@ struct fscrypt_nokey_name {
 
 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;
+	return is_dot_dotdot(str->name, str->len);
 }
 
 /**
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 03bd55069d86..2fe0f3af1a08 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1949,16 +1949,6 @@ 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/exportfs/expfs.c b/fs/exportfs/expfs.c
index dcf7d86c2ce4..07ea3d62b298 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -244,16 +244,6 @@ struct getdents_callback {
 	int sequence;		/* sequence counter */
 };
 
-/* Copied from lookup_one_common() */
-static inline bool is_dot_dotdot(const char *name, size_t len)
-{
-	if (unlikely(name[0] == '.')) {
-		if (len < 2 || (len == 2 && name[1] == '.'))
-			return true;
-	}
-	return false;
-}
-
 /*
  * A rather strange filldir function to capture
  * the name matching the specified inode number.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9043cedfa12b..322a3b8a3533 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3368,17 +3368,6 @@ 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 u8 *name, size_t len)
-{
-	if (len == 1 && name[0] == '.')
-		return true;
-
-	if (len == 2 && name[0] == '.' && name[1] == '.')
-		return true;
-
-	return false;
-}
-
 static inline void *f2fs_kmalloc(struct f2fs_sb_info *sbi,
 					size_t size, gfp_t flags)
 {
diff --git a/fs/namei.c b/fs/namei.c
index 71c13b2990b4..2386a70667fa 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2667,10 +2667,8 @@ static int lookup_one_common(struct mnt_idmap *idmap,
 	if (!len)
 		return -EACCES;
 
-	if (unlikely(name[0] == '.')) {
-		if (len < 2 || (len == 2 && name[1] == '.'))
-			return -EACCES;
-	}
+	if (is_dot_dotdot(name, len))
+		return -EACCES;
 
 	while (len--) {
 		unsigned int c = *(const unsigned char *)name++;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98b7a7a8c42e..baa64344a308 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2846,6 +2846,17 @@ extern bool path_is_under(const struct path *, const struct path *);
 
 extern char *file_path(struct file *, char *, int);
 
+/**
+ * is_dot_dotdot - returns true only if @name is "." or ".."
+ * @name: file name to check
+ * @len: length of file name, in bytes
+ */
+static inline bool is_dot_dotdot(const char *name, size_t len)
+{
+	return len && unlikely(name[0] == '.') &&
+		(len == 1 || (len == 2 && name[1] == '.'));
+}
+
 #include <linux/err.h>
 
 /* needed for stackable file system support */

Re: [PATCH v5 0/2] fix the fallback implementation of get_name

[Christian Brauner]

On Sat, Jan 20, 2024 at 08:57:40AM -0500, Chuck Lever wrote:
> Last call.
> 
> Topic branch for fs/exportfs:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git
> branch: exportfs-next

Looks good to me,
Acked-by: Christian Brauner <brauner@kernel.org>

Re: [PATCH v5 2/2] fs: Create a generic is_dot_dotdot() utility

[Eric Biggers]

On Sat, Jan 20, 2024 at 08:57:54AM -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> De-duplicate the same functionality in several places by hoisting
> the is_dot_dotdot() utility function into linux/fs.h.
> 
> Suggested-by: Amir Goldstein <amir73il@gmail.com>
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/crypto/fname.c    |    8 +-------
>  fs/ecryptfs/crypto.c |   10 ----------
>  fs/exportfs/expfs.c  |   10 ----------
>  fs/f2fs/f2fs.h       |   11 -----------
>  fs/namei.c           |    6 ++----
>  include/linux/fs.h   |   11 +++++++++++
>  6 files changed, 14 insertions(+), 42 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric