smb/server: avoid deadlock when linking with ReplaceIfExists

If smb2_create_link() is called with ReplaceIfExists set and the name
does exist then a deadlock will happen.

ksmbd_vfs_kern_path_locked() will return with success and the parent
directory will be locked.  ksmbd_vfs_remove_file() will then remove the
file.  ksmbd_vfs_link() will then be called while the parent is still
locked.  It will try to lock the same parent and will deadlock.

This patch moves the ksmbd_vfs_kern_path_unlock() call to *before*
ksmbd_vfs_link() and then simplifies the code, removing the file_present
flag variable.

Signed-off-by: NeilBrown <neil@brown.name>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 02ccdcc86af2895aca678d7a75b68cb3c1f758a3..07f567ed609c1ab91fef005ddf6142865f06ab3e 100644 (file)
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -6037,7 +6037,6 @@ static int smb2_create_link(struct ksmbd_work *work,
 {
        char *link_name = NULL, *target_name = NULL, *pathname = NULL;
        struct path path, parent_path;
-       bool file_present = false;
        int rc;
 
        if (buf_len < (u64)sizeof(struct smb2_file_link_info) +
@@ -6070,11 +6069,8 @@ static int smb2_create_link(struct ksmbd_work *work,
        if (rc) {
                if (rc != -ENOENT)
                        goto out;
-       } else
-               file_present = true;
-
-       if (file_info->ReplaceIfExists) {
-               if (file_present) {
+       } else {
+               if (file_info->ReplaceIfExists) {
                        rc = ksmbd_vfs_remove_file(work, &path);
                        if (rc) {
                                rc = -EINVAL;
@@ -6082,21 +6078,17 @@ static int smb2_create_link(struct ksmbd_work *work,
                                            link_name);
                                goto out;
                        }
-               }
-       } else {
-               if (file_present) {
+               } else {
                        rc = -EEXIST;
                        ksmbd_debug(SMB, "link already exists\n");
                        goto out;
                }
+               ksmbd_vfs_kern_path_unlock(&parent_path, &path);
        }
-
        rc = ksmbd_vfs_link(work, target_name, link_name);
        if (rc)
                rc = -EINVAL;
 out:
-       if (file_present)
-               ksmbd_vfs_kern_path_unlock(&parent_path, &path);
 
        if (!IS_ERR(link_name))
                kfree(link_name);