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Change History

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

netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry

When a write subrequest is marked NETFS_SREQ_NEED_RETRY, the retry path
in netfs_unbuffered_write() unconditionally calls stream->prepare_write()
without checking if it is NULL.

Filesystems such as 9P do not set the prepare_write operation, so
stream->prepare_write remains NULL. When get_user_pages() fails with
-EFAULT and the subrequest is flagged for retry, this results in a NULL
pointer dereference at fs/netfs/direct_write.c:189.

Fix this by mirroring the pattern already used in write_retry.c: if
stream->prepare_write is NULL, skip renegotiation and directly reissue
the subrequest via netfs_reissue_write(), which handles iterator reset,
IN_PROGRESS flag, stats update and reissue internally.

https://git.kernel.org/stable/c/7a5482f5ce891decbf36f2e6fab1e9fc4a76a684

https://git.kernel.org/stable/c/a4d1b4ba9754bac3efebd06f583a44a7af52c0ab

https://git.kernel.org/stable/c/e9075e420a1eb3b52c60f3b95893a55e77419ce8