NFS: Fix a race when updating an existing write

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: NFS: Fix a race when updating an existing write After nfs_lock_and_join_requests() tests for whether the request is still attached to the mapping, nothing prevents a call to nfs_inode_remove_request() from succeeding until we actually lock the page group. The reason is that whoever called nfs_inode_remove_request() doesn't necessarily have a lock on the page group head. So in order to avoid races, let's take the page group lock earlier in nfs_lock_and_join_requests(), and hold it across the removal of the request in nfs_inode_remove_request().

References

• https://git.kernel.org/stable/c/0ff42a32784e0f2cb46a46da8e9f473538c13e1b
• https://git.kernel.org/stable/c/f230d40147cc37eb3aef4d50e2e2c06ea73d9a77
• https://git.kernel.org/stable/c/c32e3c71aaa1c1ba05da88605e2ddd493c58794f
• https://git.kernel.org/stable/c/181feb41f0b268e6288bf9a7b984624d7fe2031d
• https://git.kernel.org/stable/c/92278ae36935a54e65fef9f8ea8efe7e80481ace
• https://git.kernel.org/stable/c/202a3432d21ac060629a760fff3b0a39859da3ea
• https://git.kernel.org/stable/c/76d2e3890fb169168c73f2e4f8375c7cc24a765e