ksmbd: discard write access to the directory open

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: discard write access to the directory open may_open() does not allow a directory to be opened with the write access. However, some writing flags set by client result in adding write access on server, making ksmbd incompatible with FUSE file system. Simply, let's discard the write access when opening a directory. list_add corruption. next is NULL. ------------[ cut here ]------------ kernel BUG at lib/list_debug.c:26! pc : __list_add_valid+0x88/0xbc lr : __list_add_valid+0x88/0xbc Call trace: __list_add_valid+0x88/0xbc fuse_finish_open+0x11c/0x170 fuse_open_common+0x284/0x5e8 fuse_dir_open+0x14/0x24 do_dentry_open+0x2a4/0x4e0 dentry_open+0x50/0x80 smb2_open+0xbe4/0x15a4 handle_ksmbd_work+0x478/0x5ec process_one_work+0x1b4/0x448 worker_thread+0x25c/0x430 kthread+0x104/0x1d4 ret_from_fork+0x10/0x20

References

• https://git.kernel.org/stable/c/66cf853e1c7a2407f15d9f7aaa3e47d61745e361
• https://git.kernel.org/stable/c/9e84b1ba5c98fb5c9f869c85db1d870354613baa
• https://git.kernel.org/stable/c/198498b2049c0f11f7670be6974570e02b0cc035
• https://git.kernel.org/stable/c/e2e33caa5dc2eae7bddf88b22ce11ec3d760e5cd