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

From: David Howells
Date: Thu Apr 04 2024 - 11:22:43 EST


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@xxxxxxxxxx>
cc: Steve French <sfrench@xxxxxxxxx>
cc: Paulo Alcantara <pc@xxxxxxxxxxxxx>
cc: Shyam Prasad N <sprasad@xxxxxxxxxxxxx>
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/smb/client/cifsglob.h | 2 ++
fs/smb/client/fscache.c | 13 +++++++++++++
fs/smb/client/misc.c | 3 +++
3 files changed, 18 insertions(+)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 7ed9d05f6890..43319288b4e3 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1275,7 +1275,9 @@ 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 340efce8f052..113bde8f1e61 100644
--- 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 @@ int cifs_fscache_get_super_cookie(struct cifs_tcon *tcon)
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 c3771fc81328..b27fbb840539 100644
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -141,6 +141,9 @@ tcon_info_alloc(bool dir_leases_enabled)
#ifdef CONFIG_CIFS_DFS_UPCALL
INIT_LIST_HEAD(&ret_buf->dfs_ses_list);
#endif
+#ifdef CONFIG_CIFS_FSCACHE
+ mutex_init(&ret_buf->fscache_lock);
+#endif

return ret_buf;
}