Fix shared upload permissions for capability-restricted LTX backend

README.md

@@ -33,7 +33,9 @@ ffmpeg only. It does not install or restart LTX, Deck, WireGuard or a GPU driver
    these files. Set file permissions so only the selected WEB_UID can read them.
    For a backend without authentication, the token file can be empty.
 4. Ensure WEB_UID/WEB_GID can write the input directory and read the output
-   directory. Do not recursively change ownership of existing LTX data.
+   directory. Use a shared group with the LTX process for inputs: a dedicated
+   input directory with mode 2750, files 0640. Both containers need this group.
+   Do not recursively change ownership of existing LTX data.
 5. Set PUBLIC_ORIGIN to the browser URL, e.g. `http://127.0.0.1:8118` for an SSH tunnel.
 6. Start: `docker compose up -d --build`.
 7. Stop: `docker compose down`. Shared media is retained; LTX keeps running.

deploy/compose.athena.yaml

@@ -3,6 +3,8 @@
 services:
   ltx-deskweb:
     container_name: ltx-deskweb
+    # Shared read group with the existing capability-restricted LTX backend.
+    user: "1000:0"
     network_mode: host
     ports: !reset []
     extra_hosts: !reset []

docs/ARCHITECTURE.md

@@ -27,6 +27,10 @@ outputs are mounted read-only. Only configured input/output roots are readable;
 traversal and symlinks escaping those roots are rejected. ffmpeg/ffprobe create
 thumbnails, dimensions and extracted frames on CPU; they are not inference runtimes.
 Network protocols are disabled for media inspection. HTTP Range supports seeking.
+Uploads, copied assets and thumbnails are mode 0640. Provision the writable input
+folder with a shared backend group and mode 2750 (setgid), so new files inherit
+that group. Both service identities must be able to traverse/read the shared
+folder; a root UID with dropped capabilities cannot bypass ordinary permissions.
 
 Projects: initial preview retains the upstream browser-local project storage.
 Projects are specific to this browser/origin, not multiuser or cross-device synced.

docs/ATHENA_DEPLOYMENT.md

@@ -7,7 +7,8 @@ The additional `deploy/compose.athena.yaml` uses host networking **only for this
 frontend**, binds its web server to `127.0.0.1:8118`, and connects to Deck at
 `http://127.0.0.1:8120`. This avoids changing Deck's existing network or relying on
 its current Docker IP. No Docker socket, GPU devices or inference packages are
-mounted into the GUI. CPU and RAM limits: 2 CPUs / 1 GiB.
+mounted into the GUI. CPU and RAM limits: 2 CPUs / 1 GiB. GUI identity: UID 1000 / GID 0;
+this supplies shared-file read access, not root UID or Linux capabilities.
 
 Filtered Deck inventory labels:
 
@@ -17,7 +18,9 @@ Filtered Deck inventory labels:
 Media mounts:
 
 - `/data/video/ltx-desktop/LTXDesktop/remote-inputs/deskweb` → writable inputs.
-  A new isolated directory owned by UID/GID 1000; no recursive permission changes.
+  A new isolated directory owned by UID 1000 / GID 0, mode 2750; no changes to other LTX directories.
+  Files use mode 0640. The existing LTX backend runs with GID 0 and dropped
+  capabilities, so group-read/traverse permission is required even for its root UID.
 - `/data/video/ltx-desktop/LTXDesktop/outputs` → read-only outputs.
 
 Backend-visible input path: `/data/LTXDesktop/remote-inputs/deskweb`.

docs/VALIDATION.md

@@ -33,3 +33,21 @@ synthetic text upload and readback through shared input storage (test file remov
 Deck's actual Unix-socket helper inventory returns `ltx-deskweb` as `running`.
 Existing Medium, TTS, WireGuard and Deck remain running; LTX remains stopped.
 Real video generation was not requested or tested in this deployment.
+
+## Shared-input permission fix — 2026-09-29
+
+A real I2V request exposed a cross-container permission error: private uploads
+(0600 in a 0750 UID/GID-1000 directory) were invisible to LTX's UID/GID-0 process
+because its container drops all Linux capabilities. Same bind mount/path did not
+imply read permission. The API reported this as “Image file not found”.
+
+Dedicated DeskWEB input directory now uses UID 1000 / GID 0, mode 2750; uploads,
+asset copies and thumbnails use 0640. Athena GUI runs as 1000:0 with capabilities
+still dropped. Only existing DeskWEB-owned input files had their permissions
+corrected; no other media directory, backend container or GPU service was changed.
+
+Validation: build/typecheck and all 8 tests pass; integration tests now assert
+0640 on uploads, copies (including a 0600 source) and thumbnails. On Athena the
+reported image's existence/read permission was verified from inside LTX without
+opening its content. A fresh synthetic upload was also checked from LTX and then
+removed. Only the GUI was recreated; real image generation remains a user retry.

server/app.mjs

@@ -1,7 +1,7 @@
 import http from 'node:http'
 import https from 'node:https'
 import { createReadStream, createWriteStream } from 'node:fs'
-import { readFile, mkdir, realpath, stat, unlink, copyFile } from 'node:fs/promises'
+import { readFile, mkdir, realpath, stat, unlink, copyFile, chmod } from 'node:fs/promises'
 import path from 'node:path'
 import { randomBytes, randomUUID, timingSafeEqual, createHash } from 'node:crypto'
 import { pipeline } from 'node:stream/promises'
@@ -119,7 +119,7 @@ export async function createApp(config) {
           if(Number(req.headers['content-length'])>limit)throw fail(413,'Upload too large')
           const target=outputName(ext);let size=0
           const limiter=new Transform({transform(chunk,_encoding,done){size+=chunk.length;done(size>limit?fail(413,'Upload too large'):null,chunk)}})
-          try {await pipeline(req,limiter,createWriteStream(target.local,{flags:'wx',mode:0o600}))} catch(e){await unlink(target.local).catch(()=>{});throw e}
+          try {await pipeline(req,limiter,createWriteStream(target.local,{flags:'wx',mode:0o640}));await chmod(target.local,0o640)} catch(e){await unlink(target.local).catch(()=>{});throw e}
           return json(res,201,{success:true,path:target.backend})
         }
         if(url.pathname==='/web/files'&&req.method==='POST') {
@@ -131,7 +131,7 @@ export async function createApp(config) {
           const source=await resolveMedia(p.path)
           if(p.action==='prepare')return json(res,200,{success:true,path:p.path})
           if(p.action==='copy') {
-            const target=outputName(path.extname(source));await copyFile(source,target.local);return json(res,200,{success:true,path:target.backend})
+            const target=outputName(path.extname(source));await copyFile(source,target.local);await chmod(target.local,0o640);return json(res,200,{success:true,path:target.backend})
           }
           if(p.action==='metadata'||p.action==='thumbnail'||p.action==='frame') {
             if(p.action==='metadata') {
@@ -143,6 +143,7 @@ export async function createApp(config) {
             if(!Number.isFinite(time)||time<0)throw fail(400,'Invalid frame time')
             const target=outputName('.jpg')
             await exec('ffmpeg',['-nostdin','-v','error','-ss',String(time),'-protocol_whitelist','file,pipe','-i',source,'-frames:v','1','-vf','scale=960:-2','-y',target.local],{timeout:60000,maxBuffer:1024*1024})
+            await chmod(target.local,0o640)
             return json(res,200,{success:true,path:target.backend,bigThumbnailPath:target.backend,smallThumbnailPath:target.backend})
           }
           throw fail(400,'Unsupported file operation')

server/app.test.mjs

@@ -1,7 +1,7 @@
 import { test } from 'node:test'
 import assert from 'node:assert/strict'
 import http from 'node:http'
-import { mkdtemp, mkdir, writeFile, readFile, symlink, rm } from 'node:fs/promises'
+import { mkdtemp, mkdir, writeFile, readFile, symlink, rm, stat, chmod } from 'node:fs/promises'
 import os from 'node:os'
 import path from 'node:path'
 import { createApp } from './app.mjs'
@@ -54,6 +54,7 @@ test('upload, backend path, range playback and existence check',async t=>{
   const {call,dir}=await fixture(t)
   const upload=await call('/web/upload?name=clip.mp4',{method:'POST',body:'0123456789'})
   assert.equal(upload.status,201);const result=await upload.json();assert.ok(result.path.startsWith('/ltx/inputs/'))
+  assert.equal((await stat(path.join(dir,'input',path.basename(result.path)))).mode & 0o777,0o640)
   assert.equal(await readFile(path.join(dir,'input',path.basename(result.path)),'utf8'),'0123456789')
   const media=await call('/web/media?path='+encodeURIComponent(result.path),{headers:{Range:'bytes=2-5'}})
   assert.equal(media.status,206);assert.equal(media.headers.get('content-range'),'bytes 2-5/10');assert.equal(await media.text(),'2345')
@@ -76,13 +77,16 @@ test('shared media can be inspected, copied and thumbnailed without an inference
   const {call,dir}=await fixture(t)
   // Deliberately tiny synthetic PPM pixels; ffprobe detects content, not extension.
   await writeFile(path.join(dir,'output','test.png'),Buffer.concat([Buffer.from('P6\n2 2\n255\n'),Buffer.from([0,0,255,0,0,255,0,0,255,0,0,255])]))
+  await chmod(path.join(dir,'output','test.png'),0o600)
   const invoke=async action=>{
     const response=await call('/web/files',{method:'POST',body:JSON.stringify({action,path:'/ltx/outputs/test.png'})})
     assert.equal(response.status,200);return response.json()
   }
   const metadata=await invoke('metadata');assert.equal(metadata.width,2);assert.equal(metadata.height,2)
   const copy=await invoke('copy');assert.ok(copy.path.startsWith('/ltx/inputs/'))
+  assert.equal((await stat(path.join(dir,'input',path.basename(copy.path)))).mode & 0o777,0o640)
   const thumbnail=await invoke('thumbnail');assert.ok(thumbnail.path.endsWith('.jpg'))
+  assert.equal((await stat(path.join(dir,'input',path.basename(thumbnail.path)))).mode & 0o777,0o640)
   const response=await call('/web/media?path='+encodeURIComponent(thumbnail.path));assert.equal(response.status,200)
   assert.equal(response.headers.get('content-type'),'image/jpeg');assert.ok((await response.arrayBuffer()).byteLength>100)
 })