https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236379
Bug ID: 236379
Summary: [FUSE] fuse(4) writes from aio(4) don't set the
fuse_out_header.pid field correctly
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: asom...@freebsd.org
Every FUSE operation includes the pid of the process that issued the request.
However, when an aiod kernel process writes to a fuse-backed file on behalf of
a regular user process, fuse(4) only sees aiod's pid_t, not the user process's.
This can cause a fuse filesystem daemon to incorrectly authenticate write
commands
There are three possible solutions:
1) Set the pid field correctly. The aio daemon already keeps track of it,
but doesn't send that information to fuse(4). It's not obvious how.
a) Perhaps stuff it into a spare field in struct ucred?
b) Define custom fileops for fuse and store the pid that opened a file in
struct file.f_data? But this would cause problems when sending a file
descriptor from one process to another with sendmsg.
2) Set FUSE_WRITE_CACHE, just like writes from the pager. Currently, however,
fuse(4) isn't aware of which operations come from aiod.
3) Alternatively, since FUSE_WRITE is an asynchronous operation, aio(4)
could learn to bypass VOP_WRITE and use a threadless direct dispatch like
it currently does for disks. That would improve performance, too.
This bug probably applies to aio reads as well, but I haven't checked yet.
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