smb: Fix regression in writes when non-standard maximum write size negotiated

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: smb: Fix regression in writes when non-standard maximum write size negotiated The conversion to netfs in the 6.3 kernel caused a regression when maximum write size is set by the server to an unexpected value which is not a multiple of 4096 (similarly if the user overrides the maximum write size by setting mount parm "wsize", but sets it to a value that is not a multiple of 4096). When negotiated write size is not a multiple of 4096 the netfs code can skip the end of the final page when doing large sequential writes, causing data corruption. This section of code is being rewritten/removed due to a large netfs change, but until that point (ie for the 6.3 kernel until now) we can not support non-standard maximum write sizes. Add a warning if a user specifies a wsize on mount that is not a multiple of 4096 (and round down), also add a change where we round down the maximum write size if the server negotiates a value that is not a multiple of 4096 (we also have to check to make sure that we do not round it down to zero).

References

• https://git.kernel.org/stable/c/4145ccff546ea868428b3e0fe6818c6261b574a9
• https://git.kernel.org/stable/c/63c35afd50e28b49c5b75542045a8c42b696dab9
• https://git.kernel.org/stable/c/4860abb91f3d7fbaf8147d54782149bb1fc45892