afs: Fix characters allowed into cell names

The afs filesystem needs to prohibit certain characters from cell names,
such as '/', as these are used to form filenames in procfs, leading to
the following warning being generated:

	WARNING: CPU: 0 PID: 3489 at fs/proc/generic.c:178

Fix afs_alloc_cell() to disallow nonprintable characters, '/', '@' and
names that begin with a dot.

Remove the check for "@cell" as that is then redundant.

This can be tested by running:

	echo add foo/.bar 1.2.3.4 >/proc/fs/afs/cells

Note that we will also need to deal with:

 - Names ending in ".invalid" shouldn't be passed to the DNS.

 - Names that contain non-valid domainname chars shouldn't be passed to
   the DNS.

 - DNS replies that say "your-dns-needs-immediate-attention.<gTLD>" and
   replies containing A records that say 127.0.53.53 should be
   considered invalid.
   [https://www.icann.org/en/system/files/files/name-collision-mitigation-01aug14-en.pdf]

but these need to be dealt with by the kafs-client DNS program rather
than the kernel.

Reported-by: syzbot+b904ba7c947a37b4b291@syzkaller.appspotmail.com
Cc: stable@kernel.org
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index fd5133e..78ba5f9 100644 (file)
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -134,8 +134,17 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
                _leave(" = -ENAMETOOLONG");
                return ERR_PTR(-ENAMETOOLONG);
        }
-       if (namelen == 5 && memcmp(name, "@cell", 5) == 0)
+
+       /* Prohibit cell names that contain unprintable chars, '/' and '@' or
+        * that begin with a dot.  This also precludes "@cell".
+        */
+       if (name[0] == '.')
                return ERR_PTR(-EINVAL);
+       for (i = 0; i < namelen; i++) {
+               char ch = name[i];
+               if (!isprint(ch) || ch == '/' || ch == '@')
+                       return ERR_PTR(-EINVAL);
+       }
 
        _enter("%*.*s,%s", namelen, namelen, name, addresses);