cifs: Fix reacquisition of volume cookie on still-live connection

During mount, cifs_mount_get_tcon() gets a tcon resource connection record
and then attaches an fscache volume cookie to it.  However, it does this
irrespective of whether or not the tcon returned from cifs_get_tcon() is a
new record or one that's already in use.  This leads to a warning about a
volume cookie collision and a leaked volume cookie because tcon->fscache
gets reset.

Fix this be adding a mutex and a "we've already tried this" flag and only
doing it once for the lifetime of the tcon.

[!] Note: Looking at cifs_mount_get_tcon(), a more general solution may
actually be required.  Reacquiring the volume cookie isn't the only thing
that function does: it also partially reinitialises the tcon record without
any locking - which may cause live filesystem ops already using the tcon
through a previous mount to malfunction.

This can be reproduced simply by something like:

    mount //example.com/test /xfstest.test -o user=shares,pass=xxx,fsc
    mount //example.com/test /mnt -o user=shares,pass=xxx,fsc

Fixes: 70431bfd825d ("cifs: Support fscache indexing rewrite")
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
cc: Shyam Prasad N <sprasad@microsoft.com>
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index d6669ce4ae87f07415b150eaffcbf429c4fe74bd..fc09d1c0ee070fc7b3ecd17e02e3872238a668ba 100644 (file)
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1276,7 +1276,9 @@ struct cifs_tcon {
        __u32 max_cached_dirs;
 #ifdef CONFIG_CIFS_FSCACHE
        u64 resource_id;                /* server resource id */
+       bool fscache_acquired;          /* T if we've tried acquiring a cookie */
        struct fscache_volume *fscache; /* cookie for share */
+       struct mutex fscache_lock;      /* Prevent regetting a cookie */
 #endif
        struct list_head pending_opens; /* list of incomplete opens */
        struct cached_fids *cfids;

diff --git a/fs/smb/client/fscache.c b/fs/smb/client/fscache.c
index 340efce8f052951a308329b70b5846d9e57477f5..113bde8f1e6133ba7270edae49116ff680e49886 100644 (file)
--- a/fs/smb/client/fscache.c
+++ b/fs/smb/client/fscache.c
@@ -43,12 +43,23 @@ int cifs_fscache_get_super_cookie(struct cifs_tcon *tcon)
        char *key;
        int ret = -ENOMEM;
 
+       if (tcon->fscache_acquired)
+               return 0;
+
+       mutex_lock(&tcon->fscache_lock);
+       if (tcon->fscache_acquired) {
+               mutex_unlock(&tcon->fscache_lock);
+               return 0;
+       }
+       tcon->fscache_acquired = true;
+
        tcon->fscache = NULL;
        switch (sa->sa_family) {
        case AF_INET:
        case AF_INET6:
                break;
        default:
+               mutex_unlock(&tcon->fscache_lock);
                cifs_dbg(VFS, "Unknown network family '%d'\n", sa->sa_family);
                return -EINVAL;
        }
@@ -57,6 +68,7 @@ int cifs_fscache_get_super_cookie(struct cifs_tcon *tcon)
 
        sharename = extract_sharename(tcon->tree_name);
        if (IS_ERR(sharename)) {
+               mutex_unlock(&tcon->fscache_lock);
                cifs_dbg(FYI, "%s: couldn't extract sharename\n", __func__);
                return PTR_ERR(sharename);
        }
@@ -90,6 +102,7 @@ out_2:
        kfree(key);
 out:
        kfree(sharename);
+       mutex_unlock(&tcon->fscache_lock);
        return ret;
 }
 

diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c
index 7d15a1969b818439515b5188e8662a3b8f1276ce..ad44f8d66b3775ce5c585b2c2b989b9d79cb623f 100644 (file)
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -139,6 +139,9 @@ tcon_info_alloc(bool dir_leases_enabled)
        atomic_set(&ret_buf->num_local_opens, 0);
        atomic_set(&ret_buf->num_remote_opens, 0);
        ret_buf->stats_from_time = ktime_get_real_seconds();
+#ifdef CONFIG_CIFS_FSCACHE
+       mutex_init(&ret_buf->fscache_lock);
+#endif
 
        return ret_buf;
 }