Patch "cifs: return ENAMETOOLONG for overlong names in cifs_open()/cifs_lookup()" has been added to the 4.12-stable tree

This is a note to let you know that I've just added the patch titled

cifs: return ENAMETOOLONG for overlong names in cifs_open()/cifs_lookup()

to the 4.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cifs-return-enametoolong-for-overlong-names-in-cifs_open-cifs_lookup.patch
and it can be found in the queue-4.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ronnie Sahlberg <[email protected]>
Date: Wed, 23 Aug 2017 14:48:14 +1000
Subject: cifs: return ENAMETOOLONG for overlong names in cifs_open()/cifs_lookup()

From: Ronnie Sahlberg <[email protected]>

commit d3edede29f74d335f81d95a4588f5f136a9f7dcf upstream.

Add checking for the path component length and verify it is <= the maximum that the server advertizes via FileFsAttributeInformation.

With this patch cifs.ko will now return ENAMETOOLONG instead of ENOENT when users to access an overlong path.

To test this, try to cd into a (non-existing) directory on a CIFS share that has a too long name:
cd /mnt/aaaaaaaaaaaaaaa...

and it now should show a good error message from the shell:
bash: cd: /mnt/aaaaaaaaaaaaaaaa...aaaaaa: File name too long

rh bz 1153996

---
 fs/cifs/dir.c |   18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

@@ -194,15 +194,20 @@ cifs_bp_rename_retry:
 }
 
 /*
+ * Don't allow path components longer than the server max.
  * Don't allow the separator character in a path component.
  * The VFS will not allow "/", but "\" is allowed by posix.
  */
 static int
-check_name(struct dentry *direntry)
+check_name(struct dentry *direntry, struct cifs_tcon *tcon)
 {
 	struct cifs_sb_info *cifs_sb = CIFS_SB(direntry->d_sb);
 	int i;
 
+	if (unlikely(direntry->d_name.len >
+		     tcon->fsAttrInfo.MaxPathNameComponentLength))
+		return -ENAMETOOLONG;
+
 	if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_POSIX_PATHS)) {
 		for (i = 0; i < direntry->d_name.len; i++) {
 			if (direntry->d_name.name[i] == '\\') {

@@ -500,10 +505,6 @@ cifs_atomic_open(struct inode *inode, st
 		return finish_no_open(file, res);
 	}
 
-	rc = check_name(direntry);
-	if (rc)
-		return rc;
-
 	xid = get_xid();
 
 	cifs_dbg(FYI, "parent inode = 0x%p name is: %pd and dentry = 0x%p\n",

@@ -516,6 +517,11 @@ cifs_atomic_open(struct inode *inode, st
 	}
 
 	tcon = tlink_tcon(tlink);
+
+	rc = check_name(direntry, tcon);
+	if (rc)
+		goto out_free_xid;
+
 	server = tcon->ses->server;
 
 	if (server->ops->new_lease_key)

@@ -776,7 +782,7 @@ cifs_lookup(struct inode *parent_dir_ino
 	}
 	pTcon = tlink_tcon(tlink);
 
-	rc = check_name(direntry);
+	rc = check_name(direntry, pTcon);
 	if (rc)
 		goto lookup_out;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.12/cifs-return-enametoolong-for-overlong-names-in-cifs_open-cifs_lookup.patch