Executive brief
A logic error was identified in the Linux kernel's network filesystem (netfs) component, which handles how data is written to network-attached storage. The system was unnecessarily disabling a performance feature called 'write streaming' when a file was opened for both reading and writing. While primarily a performance and stability fix, this issue could cause unexpected behavior or errors in applications performing heavy simultaneous read/write operations on network drives.
Technical details
A vulnerability in the Linux kernel's netfs library was resolved regarding the management of 'write streaming' in netfs_perform_write(). Previously, write streaming (caching dirty data in non-uptodate folios to avoid unnecessary reads) was disabled if the file descriptor was opened with O_RDWR (FMODE_READ). This was originally intended to prevent the need to flush streaming pages before a read, but the logic was redundant as netfs now handles gap-filling via read_folio(). The restriction also failed to account for separate file descriptors opened for reading. The fix removes the O_RDWR check, allowing streaming writes to proceed correctly. This issue was notably triggered during generic/522 xfstests.
Affected products
- Linux Linux Kernel 6.8 to 7.0.11
Timeline
- 2026-05-12: patched: Initial fix commit by David Howells
- 2026-07-19: disclosed: CVE published to NVD