[chore] ffmpeg webassembly fiddling (#4454)

This disables ffmpeg / ffprobe support on platforms where the wazero compiler is not available. The slowness introduced is hard to pindown for admins (and us!), so it's easier to just return an error message linking to docs on attempted media processing. It still allows the instance to run, just erroring if anything other than a jpeg is attempted to be processed. This should hopefully make it easier for users to notice these issues.

Also further locks down our wazero 'allowFiles' fs and other media code to address: https://codeberg.org/superseriousbusiness/gotosocial/issues/4408

relates to: https://codeberg.org/superseriousbusiness/gotosocial/issues/4427
also relates to issues raised in #gotosocial-help on matrix

closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4408

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4454
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

1 files changed, 13 insertions, 35 deletions

diff --git a/internal/media/ffmpeg.go b/internal/media/ffmpeg.go
index d98e93baf..938a10894 100644
--- a/internal/media/ffmpeg.go
+++ b/internal/media/ffmpeg.go
@@ -21,8 +21,6 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
-	"os"
-	"path"
 	"strconv"
 	"strings"
 
@@ -158,34 +156,20 @@ func ffmpeg(ctx context.Context, inpath string, outpath string, args ...string)
 		Config: func(modcfg wazero.ModuleConfig) wazero.ModuleConfig {
 			fscfg := wazero.NewFSConfig()
 
-			// Needs read-only access to
-			// /dev/urandom for some types.
-			urandom := &allowFiles{
-				{
-					abs:  "/dev/urandom",
-					flag: os.O_RDONLY,
-					perm: 0,
-				},
-			}
-			fscfg = fscfg.WithFSMount(urandom, "/dev")
+			// Needs read-only access /dev/urandom,
+			// required by some ffmpeg operations.
+			fscfg = fscfg.WithFSMount(&allowFiles{
+				allowRead("/dev/urandom"),
+			}, "/dev")
 
 			// In+out dirs are always the same (tmp),
 			// so we can share one file system for
 			// both + grant different perms to inpath
 			// (read only) and outpath (read+write).
-			shared := &allowFiles{
-				{
-					abs:  inpath,
-					flag: os.O_RDONLY,
-					perm: 0,
-				},
-				{
-					abs:  outpath,
-					flag: os.O_RDWR | os.O_CREATE | os.O_TRUNC,
-					perm: 0666,
-				},
-			}
-			fscfg = fscfg.WithFSMount(shared, path.Dir(inpath))
+			fscfg = fscfg.WithFSMount(&allowFiles{
+				allowCreate(outpath),
+				allowRead(inpath),
+			}, tmpdir)
 
 			// Set anonymous module name.
 			modcfg = modcfg.WithName("")
@@ -246,16 +230,10 @@ func ffprobe(ctx context.Context, filepath string) (*result, error) {
 		Config: func(modcfg wazero.ModuleConfig) wazero.ModuleConfig {
 			fscfg := wazero.NewFSConfig()
 
-			// Needs read-only access
-			// to file being probed.
-			in := &allowFiles{
-				{
-					abs:  filepath,
-					flag: os.O_RDONLY,
-					perm: 0,
-				},
-			}
-			fscfg = fscfg.WithFSMount(in, path.Dir(filepath))
+			// Needs read-only access to probed file.
+			fscfg = fscfg.WithFSMount(&allowFiles{
+				allowRead(filepath),
+			}, tmpdir)
 
 			// Set anonymous module name.
 			modcfg = modcfg.WithName("")