afs: Fix the maximum cell name length

[ Upstream commit 8fd56ad6e7c90ac2bddb0741c6b248c8c5d56ac8 ]

The kafs filesystem limits the maximum length of a cell to 256 bytes, but a
problem occurs if someone actually does that: kafs tries to create a
directory under /proc/net/afs/ with the name of the cell, but that fails
with a warning:

        WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:405

because procfs limits the maximum filename length to 255.

However, the DNS limits the maximum lookup length and, by extension, the
maximum cell name, to 255 less two (length count and trailing NUL).

Fix this by limiting the maximum acceptable cellname length to 253.  This
also allows us to be sure we can create the "/afs/.<cell>/" mountpoint too.

Further, split the YFS VL record cell name maximum to be the 256 allowed by
the protocol and ignore the record retrieved by YFSVL.GetCellName if it
exceeds 253.

Fixes: c3e9f888263b ("afs: Implement client support for the YFSVL.GetCellName RPC op")
Reported-by: syzbot+7848fee1f1e5c53f912b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/6776d25d.050a0220.3a8527.0048.GAE@google.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/376236.1736180460@warthog.procyon.org.uk
Tested-by: syzbot+7848fee1f1e5c53f912b@syzkaller.appspotmail.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/afs/afs.h b/fs/afs/afs.h
index 432cb4b23961424776b05d56f40962eb9bc2356b..3ea5f3e3c922a32fbe0ff3bec5fd364341356110 100644 (file)
--- a/fs/afs/afs.h
+++ b/fs/afs/afs.h
@@ -10,7 +10,7 @@
 
 #include <linux/in.h>
 
-#define AFS_MAXCELLNAME                256     /* Maximum length of a cell name */
+#define AFS_MAXCELLNAME                253     /* Maximum length of a cell name (DNS limited) */
 #define AFS_MAXVOLNAME         64      /* Maximum length of a volume name */
 #define AFS_MAXNSERVERS                8       /* Maximum servers in a basic volume record */
 #define AFS_NMAXNSERVERS       13      /* Maximum servers in a N/U-class volume record */

diff --git a/fs/afs/afs_vl.h b/fs/afs/afs_vl.h
index 9c65ffb8a523bd90debe526c7eda4872a0336d98..8da0899fbc0835a6c772d2ff83cc14946274cc1c 100644 (file)
--- a/fs/afs/afs_vl.h
+++ b/fs/afs/afs_vl.h
@@ -13,6 +13,7 @@
 #define AFS_VL_PORT            7003    /* volume location service port */
 #define VL_SERVICE             52      /* RxRPC service ID for the Volume Location service */
 #define YFS_VL_SERVICE         2503    /* Service ID for AuriStor upgraded VL service */
+#define YFS_VL_MAXCELLNAME     256     /* Maximum length of a cell name in YFS protocol */
 
 enum AFSVL_Operations {
        VLGETENTRYBYID          = 503,  /* AFS Get VLDB entry by ID */

diff --git a/fs/afs/vl_alias.c b/fs/afs/vl_alias.c
index f04a80e4f5c3fa87c26849c757c5dba044db210f..83cf1bfbe343ae61316c8d5d513540cc57ea4c39 100644 (file)
--- a/fs/afs/vl_alias.c
+++ b/fs/afs/vl_alias.c
@@ -302,6 +302,7 @@ static char *afs_vl_get_cell_name(struct afs_cell *cell, struct key *key)
 static int yfs_check_canonical_cell_name(struct afs_cell *cell, struct key *key)
 {
        struct afs_cell *master;
+       size_t name_len;
        char *cell_name;
 
        cell_name = afs_vl_get_cell_name(cell, key);
@@ -313,8 +314,11 @@ static int yfs_check_canonical_cell_name(struct afs_cell *cell, struct key *key)
                return 0;
        }
 
-       master = afs_lookup_cell(cell->net, cell_name, strlen(cell_name),
-                                NULL, false);
+       name_len = strlen(cell_name);
+       if (!name_len || name_len > AFS_MAXCELLNAME)
+               master = ERR_PTR(-EOPNOTSUPP);
+       else
+               master = afs_lookup_cell(cell->net, cell_name, name_len, NULL, false);
        kfree(cell_name);
        if (IS_ERR(master))
                return PTR_ERR(master);

diff --git a/fs/afs/vlclient.c b/fs/afs/vlclient.c
index dc9327332f069067fe1204cab325916054e060bf..882f0727c3cd3d0f0257c26a24866fa022bcf99d 100644 (file)
--- a/fs/afs/vlclient.c
+++ b/fs/afs/vlclient.c
@@ -670,7 +670,7 @@ static int afs_deliver_yfsvl_get_cell_name(struct afs_call *call)
                        return ret;
 
                namesz = ntohl(call->tmp);
-               if (namesz > AFS_MAXCELLNAME)
+               if (namesz > YFS_VL_MAXCELLNAME)
                        return afs_protocol_error(call, afs_eproto_cellname_len);
                paddedsz = (namesz + 3) & ~3;
                call->count = namesz;