Bug 1255

Summary:	Standalone shell hush can no longer exec applets
Product:	Busybox	Reporter:	Simon Griffin <grifsim>
Component:	Other	Assignee:	unassigned
Status:	RESOLVED FIXED
Severity:	minor	CC:	busybox-cvs
Priority:	P5
Version:	1.16.x
Target Milestone:	---
Hardware:	PC
OS:	Linux
Host:		Target:
Build:

Description Simon Griffin 2010-03-10 20:31:55 UTC

I have been using "exec switch_root /mnt/new_root /sbin/init" from an initramfs successfully with hush / busybox 1.15.3 and earlier versions.  But this command stopped working when I upgraded to 1.16.0 today...

   sh: can't execute 'switch_root': No such file or directory
   Kernel panic - not syncing: Attempted to kill init!

Simple workarounds are to use ash instead of hush or not to use the standalone shell mode.

This issue was introduced with the following commit:

http://git.busybox.net/busybox/commit/?id=3ef4f77620a9f5f9a7c1247e29ea9c14e07b8a30


Steps to reproduce:

* Compile latest busybox using...

CONFIG_HUSH=y
CONFIG_FEATURE_SH_STANDALONE=y
CONFIG_INSTALL_APPLET_DONT=y

* start hush and exec an applet, e.g. hush itself...

$ busybox hush -c 'exec hush'
hush: can't execute 'hush': No such file or directory


The expected result is the same result as with either of these:

$ busybox hush -c 'exec busybox hush'
$ busybox ash -c 'exec hush'

Comment 1 Denys Vlasenko 2010-03-21 18:43:05 UTC

You also need CONFIG_FEATURE_PREFER_APPLETS=y

With the following config:

# grep ^CON .config
CONFIG_HAVE_DOT_CONFIG=y
CONFIG_INCLUDE_SUSv2=y
CONFIG_FEATURE_BUFFERS_USE_MALLOC=y
CONFIG_SHOW_USAGE=y
CONFIG_FEATURE_COMPRESS_USAGE=y
CONFIG_SUBST_WCHAR=0
CONFIG_LAST_SUPPORTED_WCHAR=0
CONFIG_LONG_OPTS=y
CONFIG_FEATURE_DEVPTS=y
CONFIG_FEATURE_PREFER_APPLETS=y
CONFIG_BUSYBOX_EXEC_PATH="/proc/self/exe"
CONFIG_CROSS_COMPILER_PREFIX=""
CONFIG_EXTRA_CFLAGS=""
CONFIG_NO_DEBUG_LIB=y
CONFIG_INSTALL_APPLET_SYMLINKS=y
CONFIG_PREFIX="./_install"
CONFIG_PASSWORD_MINLEN=6
CONFIG_MD5_SIZE_VS_SPEED=2
CONFIG_FEATURE_EDITING_MAX_LEN=0
CONFIG_FEATURE_EDITING_HISTORY=0
CONFIG_FEATURE_NON_POSIX_CP=y
CONFIG_FEATURE_COPYBUF_KB=4
CONFIG_MONOTONIC_SYSCALL=y
CONFIG_IOCTL_HEX2STR_ERROR=y
CONFIG_FEATURE_HWIB=y
CONFIG_ECHO=y
CONFIG_FEATURE_FANCY_ECHO=y
CONFIG_DEFAULT_SETFONT_DIR=""
CONFIG_FEATURE_VI_MAX_LEN=0
CONFIG_FEATURE_KILL_DELAY=0
CONFIG_TELINIT_PATH=""
CONFIG_USE_BB_CRYPT=y
CONFIG_FIRST_SYSTEM_ID=0
CONFIG_LAST_SYSTEM_ID=0
CONFIG_DEFAULT_MODULES_DIR=""
CONFIG_DEFAULT_DEPMOD_FILE=""
CONFIG_FSCK_MINIX=y
CONFIG_FEATURE_MINIX2=y
CONFIG_FEATURE_BEEP_FREQ=0
CONFIG_FEATURE_BEEP_LENGTH_MS=0
CONFIG_FEATURE_CROND_DIR=""
CONFIG_FEATURE_LESS_MAXLINES=0
CONFIG_IFUPDOWN_IFSTATE_PATH=""
CONFIG_DHCPD_LEASES_FILE=""
CONFIG_UDHCP_DEBUG=0
CONFIG_UDHCPC_DEFAULT_SCRIPT=""
CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS=0
CONFIG_IFUPDOWN_UDHCPC_CMD_OPTIONS=""
CONFIG_FEATURE_MIME_CHARSET=""
CONFIG_SV_DEFAULT_SERVICE_DIR=""
CONFIG_FEATURE_SH_IS_NONE=y
CONFIG_HUSH=y
CONFIG_HUSH_BASH_COMPAT=y
CONFIG_HUSH_INTERACTIVE=y
CONFIG_SH_MATH_SUPPORT=y
CONFIG_FEATURE_SH_STANDALONE=y
CONFIG_FEATURE_IPC_SYSLOG_BUFFER_SIZE=0

I see the following behavior: "cp" fails as expected (I dont have this applet enabled, and PATH is ""), but enabled applet "fsck.minix" works:

# PATH= ./busybox hush


BusyBox v1.17.0.git (2010-03-21 19:15:47 CET) hush - the humble shell

/.1/usr/srcdevel/bbox/fix/busybox.z7 # cp
hush: can't execute 'cp': No such file or directory
/.1/usr/srcdevel/bbox/fix/busybox.z7 # fsck.minix
BusyBox v1.17.0.git (2010-03-21 19:15:47 CET) multi-call binary.

Usage: fsck.minix [-larvsmf] BLOCKDEV

/.1/usr/srcdevel/bbox/fix/busybox.z7 #

Comment 2 Simon Griffin 2010-03-21 21:15:34 UTC

(In reply to comment #1)
> You also need CONFIG_FEATURE_PREFER_APPLETS=y
> 
Yes, I have that one enabled as well. Pretty much goes without saying since FEATURE_SH_STANDALONE depends on: (MSH || LASH || HUSH || ASH) && FEATURE_PREFER_APPLETS


> I see the following behavior: "cp" fails as expected (I dont have this applet
> enabled, and PATH is ""), but enabled applet "fsck.minix" works:
> 
> # PATH= ./busybox hush
> 
> 
> BusyBox v1.17.0.git (2010-03-21 19:15:47 CET) hush - the humble shell
> 
> /.1/usr/srcdevel/bbox/fix/busybox.z7 # cp
> hush: can't execute 'cp': No such file or directory
> /.1/usr/srcdevel/bbox/fix/busybox.z7 # fsck.minix
> BusyBox v1.17.0.git (2010-03-21 19:15:47 CET) multi-call binary.
> 
> Usage: fsck.minix [-larvsmf] BLOCKDEV
> 
> /.1/usr/srcdevel/bbox/fix/busybox.z7 #
> 

Here is what I get using your .config:


~/src/busybox-git$ PATH= ./busybox hush


BusyBox v1.17.0.git (2010-03-21 21:53:25 CET) hush - the humble shell

/home/simon/src/busybox-git $ cp        
hush: can't execute 'cp': No such file or directory
/home/simon/src/busybox-git $ fsck.minix
BusyBox v1.17.0.git (2010-03-21 21:53:25 CET) multi-call binary.

Usage: fsck.minix [-larvsmf] BLOCKDEV

/home/simon/src/busybox-git $ exec fsck.minix
hush: can't execute 'fsck.minix': No such file or directory
~/src/busybox-git$ 


No problem at all until I try to "exec" an applet that worked without "exec". This only fails with hush, never ash, and only from commit 3ef4f77620a9f5f9a7c1247e29ea9c14e07b8a30 and onwards.

Comment 3 Denys Vlasenko 2010-03-22 00:47:41 UTC

AHA!

The fix is simple.

Try this:

http://busybox.net/downloads/fixes-1.16.0/busybox-1.16.0-hush.patch

Comment 4 Simon Griffin 2010-03-22 01:23:53 UTC

(In reply to comment #3)
> AHA!
> 
> The fix is simple.
> 
> Try this:
> 
> http://busybox.net/downloads/fixes-1.16.0/busybox-1.16.0-hush.patch
> 


That patch did the trick. It works great on my end.
Thanks a lot!