smb/server: avoid deadlock when linking with ReplaceIfExists

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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.

References

• https://git.kernel.org/stable/c/9d5012ffe14120f978ee34aef4df3d6cb026b7c4
• https://git.kernel.org/stable/c/ac98d54630d5b52e3f684d872f0d82c06c418ea9
• https://git.kernel.org/stable/c/1e858a7a51c7b8b009d8f246de7ceb7743b44a71
• https://git.kernel.org/stable/c/814cfdb6358d9b84fcbec9918c8f938cc096a43a
• https://git.kernel.org/stable/c/a7dddd62578c2eb6cb28b8835556a121b5157323
• https://git.kernel.org/stable/c/a726fef6d7d4cfc365d3434e3916dbfe78991a33
• https://git.kernel.org/stable/c/d5fc1400a34b4ea5e8f2ce296ea12bf8c8421694