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luci-mod-system: permit sysupgrade --create-backup over rpcd #8947

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luci-mod-system: permit sysupgrade --create-backup over rpcd #8947

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luci-mod-system: permit sysupgrade --create-backup over rpcd
JuliusBairaktaris Aug 15, 2026
7b773aa
luci-mod-status: grant the legacy iptables-save variants over rpcd
JuliusBairaktaris Aug 15, 2026
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3 changes: 2 additions & 1 deletion modules/luci-mod-system/root/usr/share/rpcd/acl.d/luci-mod-system.json
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Expand Up @@ -176,7 +176,8 @@
"/proc/mtd": [ "read" ],
"/proc/partitions": [ "read" ],
"/proc/sys/kernel/hostname": [ "read" ],
"/sbin/sysupgrade --list-backup": [ "exec" ]
"/sbin/sysupgrade --list-backup": [ "exec" ],
"/sbin/sysupgrade --create-backup -": [ "exec" ]

@openwrt-ai openwrt-ai Aug 15, 2026

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The ACL string itself looks right: rpcd checks the bare executable first and then executable + " " + each param joined with spaces (rpc_file_exec_run() file.c:1055-1083), so this is an exact match for today's execl("/sbin/sysupgrade", "/sbin/sysupgrade", "--create-backup", "-", NULL) in cgi-io, and the read section next to --list-backup is the right home for it.

What I can't square is the transport. --create-backup - emits a gzip stream on stdout, and rpcd's file.exec cannot carry that payload:

  • stdout is copied into a NUL-terminated blobmsg string (rpc_ustream_to_blobmsg() file.c:889-909), so the archive is cut at the first NUL byte;
  • the ustream read buffer is capped at RPC_FILE_MAX_SIZE = 4096 * 64 = 256 KB (file.c:46, file.c:57-59), and filling it aborts the call with UBUS_STATUS_NOT_SUPPORTED (file.c:982-989);
  • rpcd master has no fd-passing/streaming exec variant, so there is no way around the buffer.

That limit is precisely why cgi-io exists in the first place — fs.exec_direct() docs, fs.js:404-407 describe /cgi-bin/cgi-exec as the path for "large command outputs which might exceed the ubus message size limits or which contain binary data", and flash.js:83 posts the backup form straight at cgi-backup.

So: does openwrt/cgi-io#6 still spawn and stream the child's stdout to the HTTP client itself, using rpcd only for the privileged spawn / ACL check, or does it go through ubus call file exec? If the latter, any backup over 256 KB (i.e. most of them) fails outright and smaller ones come back truncated at the first NUL. I couldn't read that PR from here, so this may already be handled — worth stating in the commit message either way, since the ACL grant is the only visible half.

The same question applies to the luci-mod-status hunk in this PR: iptables-save / ip6tables-save output on a large ruleset also runs past 256 KB.

Generated by Claude Code

},
"ubus": {
"file": [ "exec", "read", "stat" ]
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