Re: [PATCH] netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry

[Christian Brauner]

On Sat, 07 Mar 2026 10:09:47 +0530, Deepanshu Kartikey wrote:
> 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.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry
      https://git.kernel.org/vfs/vfs/c/e9075e420a1e