android - 为何 su 程序一定要放到 /system/bin 目录下?

Question

各位好，请教个问题。

是否 su 程序不放到 /system/bin 目录下就没效了？

我是这样做的，用ro.kernel.qemu=1获得 adb 的 root 权限，adb shell id 是 0.0，这个时候扔个 busybox 和 su 程序到新目录 /data/tmpsos 的目录下，文件夹赋权 777，busybox 和 su 赋权 4777，然后用 adb shell "/data/tmpsos/su -c \"/data/tmpsos/busybox mount -r /dev/block/mmcblk0p2 /data/tmpsos/aso\""，命令执行成功，但是我把 adb 改回正常模式，再执行这条指令，就提示没权限了。

是不是 su 程序一定要放到 /system/bin 目录呢？

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补充说明

机器的mount情况如下，没发现noexec限制。

rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,relatime,mode=600 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,relatime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,relatime,mode=755,gid=1000 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/mmcblk0p2 /system ext4 ro,relatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p3 /data ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered,noauto_da_alloc 0 0
/dev/block/mmcblk0p4 /data/cache ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p5 /data/calibration ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered 0 0
/dev/block/vold/179:1 /mnt/sdcard vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/vold/179:1 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0 tmpfs /mnt/sdcard/.android_secure tmpfs ro,relatime,size=0k,mode=000 0 0
/dev/block/dm-0 /mnt/asec/com.camigomedia.mewantbamboo-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-1 /mnt/asec/com.intsig.camdict-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-2 /mnt/asec/com.imangi.templerun-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-3 /mnt/asec/com.omesoft.hypnotherapist-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-4 /mnt/asec/com.halfbrick.fruitninjafree-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-5 /mnt/asec/com.mybo.ponon-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-6 /mnt/asec/com.outfit7.talkingtompro-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-7 /mnt/asec/cn.dxy.medicinehelper-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-8 /mnt/asec/com.KelliNoda.Battleheart-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-9 /mnt/asec/com.fluik.OfficeJerkFree-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-10 /mnt/asec/com.UCMobile-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-11 /mnt/asec/com.forthblue.pool-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-12 /mnt/asec/com.wochacha-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-13 /mnt/asec/pl.idreams.CanKnockdown2-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-14 /mnt/asec/com.fingersoft.cartooncamera-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-15 /mnt/asec/com.disney.WMW-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-16 /mnt/asec/com.angrymobgames.muffinknightfree-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-17 /mnt/asec/com.gau.go.launcherex.gowidget.switchwidget-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-18 /mnt/asec/com.jiasoft.highrail-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-19 /mnt/asec/hotcard.net-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-20 /mnt/asec/com.dedalord.runningfred-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-21 /mnt/asec/org.cocos2dx.FishGame-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-22 /mnt/asec/com.tencent.mtt-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-23 /mnt/asec/com.feelingtouch.NinjaRun-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-24 /mnt/asec/com.iiseeuu.zhaoyaojing-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-25 /mnt/asec/info.rguide.gzmtr-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-26 /mnt/asec/com.gau.go.launcherex.gowidget.clockwidget-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-27 /mnt/asec/com.gau.go.launcherex.gowidget.notewidget-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-28 /mnt/asec/com.mt.mtxx.mtxx-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-29 /mnt/asec/com.outfit7.talkingtom2free-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-30 /mnt/asec/com.jb.gosms-2 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-31 /mnt/asec/com.likeapp.game.bubbleshooter-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-32 /mnt/asec/com.mobilicos.howtomakeorigami-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0
/dev/block/dm-33 /mnt/asec/com.omesoft.firstaid-1 vfat ro,dirsync,nosuid,nodev,relatime,uid=1000,fmask=0222,dmask=0222,codepage=cp437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0

Answer 1

/dev/block/mmcblk0p3 /data ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered,noauto_da_alloc 0 0

这里/data/tmpsos/su所在的/data分区是设置了nosuid的了。
su必须设置suid才可以正常使用

Answer 2

你要同時看看mount point的掛點是否有noexec的授權限制

/dev/block/mmcblk0p2 /system ext4 ro,relatime,barrier=1,data=ordered 0 0
/dev/block/mmcblk0p3 /data ext4 rw,nosuid,nodev,noatime,barrier=1,data=ordered,noauto_da_alloc 0 0

/system 為只讀你改不了, data nosuid 不能suid, 所是你還是不能用, 但你假設的su一定要在/system是不對的