linux-kernel - [PATCH 5.4 034/104] afs: Fix characters allowed into cell names

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Date:   Tue, 28 Jan 2020 14:59:55 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+b904ba7c947a37b4b291@...kaller.appspotmail.com,
        stable@...nel.org, David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.4 034/104] afs: Fix characters allowed into cell names

From: David Howells <dhowells@...hat.com>

commit a45ea48e2bcd92c1f678b794f488ca0bda9835b8 upstream.

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@...kaller.appspotmail.com
Cc: stable@...nel.org
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/afs/cell.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -134,8 +134,17 @@ static struct afs_cell *afs_alloc_cell(s
 		_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);