smb: client: discard post-EOF pagecache when extending a file via zero range

Overview

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

smb: client: discard post-EOF pagecache when extending a file via zero range

smb3_zero_range() removed the pagecache only for the range being zeroed, so when it extends the file the folio straddling the old EOF - which may hold data dirtied past EOF through an mmap - was never dropped and became visible as file content once the file was extended.

Lower the discard boundary to the smaller of the zero-range offset and the old EOF.

Affected

• Linux >= 72c419d9b073628d3b5b0b2fc787b724f1a8c726 < 94949b6b2f2bf0dba2e8786aed0b08cc6bc3a183
• Linux >= 72c419d9b073628d3b5b0b2fc787b724f1a8c726 < b75dadb50a25eed525264bf6fea44fad94e7626f
• Linux >= 72c419d9b073628d3b5b0b2fc787b724f1a8c726 < 6a8279c98ad289b27c0bdb11adb3f0c0b7fd456d
• Linux >= 72c419d9b073628d3b5b0b2fc787b724f1a8c726 < da4fe97fb6c730d9c94a115c7bfa6f98e0d578d0
• Linux 5.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.