ksmbd: fix race condition with fp

fp can used in each command. If smb2_close command is coming at the
same time, UAF issue can happen by race condition.

                           Time
                            +
Thread A                    | Thread B1 B2 .... B5
smb2_open                   | smb2_close
                            |
 __open_id                  |
   insert fp to file_table  |
                            |
                            |   atomic_dec_and_test(&fp->refcount)
                            |   if fp->refcount == 0, free fp by kfree.
 // UAF!                    |
 use fp                     |
                            +
This patch add f_state not to use freed fp is used and not to free fp in
use.

Reported-by: luosili <rootlab@huawei.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 20 insertions, 3 deletions

diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c
index f41f8d6108ce..c4b80ab7df74 100644
--- a/fs/smb/server/vfs_cache.c
+++ b/fs/smb/server/vfs_cache.c
@@ -333,6 +333,9 @@ static void __ksmbd_close_fd(struct ksmbd_file_table *ft, struct ksmbd_file *fp)
 
 static struct ksmbd_file *ksmbd_fp_get(struct ksmbd_file *fp)
 {
+	if (fp->f_state != FP_INITED)
+		return NULL;
+
 	if (!atomic_inc_not_zero(&fp->refcount))
 		return NULL;
 	return fp;
@@ -382,15 +385,20 @@ int ksmbd_close_fd(struct ksmbd_work *work, u64 id)
 		return 0;
 
 	ft = &work->sess->file_table;
-	read_lock(&ft->lock);
+	write_lock(&ft->lock);
 	fp = idr_find(ft->idr, id);
 	if (fp) {
 		set_close_state_blocked_works(fp);
 
-		if (!atomic_dec_and_test(&fp->refcount))
+		if (fp->f_state != FP_INITED)
 			fp = NULL;
+		else {
+			fp->f_state = FP_CLOSED;
+			if (!atomic_dec_and_test(&fp->refcount))
+				fp = NULL;
+		}
 	}
-	read_unlock(&ft->lock);
+	write_unlock(&ft->lock);
 
 	if (!fp)
 		return -EINVAL;
@@ -570,6 +578,7 @@ struct ksmbd_file *ksmbd_open_fd(struct ksmbd_work *work, struct file *filp)
 	fp->tcon		= work->tcon;
 	fp->volatile_id		= KSMBD_NO_FID;
 	fp->persistent_id	= KSMBD_NO_FID;
+	fp->f_state		= FP_NEW;
 	fp->f_ci		= ksmbd_inode_get(fp);
 
 	if (!fp->f_ci) {
@@ -591,6 +600,14 @@ err_out:
 	return ERR_PTR(ret);
 }
 
+void ksmbd_update_fstate(struct ksmbd_file_table *ft, struct ksmbd_file *fp,
+			 unsigned int state)
+{
+	write_lock(&ft->lock);
+	fp->f_state = state;
+	write_unlock(&ft->lock);
+}
+
 static int
 __close_file_table_ids(struct ksmbd_file_table *ft,
 		       struct ksmbd_tree_connect *tcon,