Solution for your grep script

[infamousrev]

The script located at:
https://github.com/MAVProxyUser/P0VsRedHerring/blob/master/grep

Does not work properly, it tries to activate adb, but logging in with adb won't work.

This is because the login script of adb runs grep in its initialisation (Causing Login->grep->restart-adb->failure).

I suggest either (this will activate adb quite late in boot):

echo /system/bin/adb_en.sh >> /system/bin/start_dji_system.sh

Or if you think that is too risky simply:

/system/bin/adb_en.sh&
/system/xbin/busybox nc -l -p 1234 -e /system/bin/sh&

Will offer a fairly risk free approach, however restoring grep function is an important thing to consider.

Or something like this:

#Mount system rw
mount -o remount,rw /system
#Select all lines before the debug check
cat /system/bin/start_dji_system.sh | /system/bin/grep -B10000 'setprop dji.sdrs 1' > /system/bin/start_dji_system.sh1
#Add line to activate adb
echo /system/bin/adb_en.sh > /system/bin/start_dji_system.sh2
#Select all lines after the debug check
cat /system/bin/start_dji_system.sh | /system/bin/grep -A10000 'setprop dji.sdrs_log 1' > /system/bin/start_dji_system.sh3
#Merge files
cat /system/bin/start_dji_system.sh1 /system/bin/start_dji_system.sh2 /system/bin/start_dji_system.sh3 > /system/bin/start_dji_system.sh4
#change permissions
chmod 755 /system/bin/start_dji_system.sh4
chown root:shell /system/bin/start_dji_system.sh4
#TODO: Add Sanity check
#replace restart script with modified variant
cp -a /system/bin/start_dji_system.sh4 /system/bin/start_dji_system.sh

[samuelsadok]

Another approach would be to make the grep hook transparent to the caller and launch custom startup code in a forked process. This way you can also safely make the hack persistent.

Like this:

self="$0"

# Comment these out to make RedHerring persistent
# mv /data/.bin/grep /data/.bin/grep.disarmed &>/dev/null
# self="/data/.bin/grep.disarmed"

/system/xbin/busybox touch /data/InYourGrill.$$

# If this is the first execution, restart myself in background with "--pwn" argument
if mkdir /tmp/RedHerring &>/dev/null; then
        mkdir /data/RedHerring &>/dev/null
        ( /system/xbin/busybox sh "$self" --pwn > /data/RedHerring/log.txt & )
fi

# Give control to the real grep unless started with --pwn
[ "$1" == "--pwn" ] || exec /system/xbin/busybox grep "$@"

### Beginning of persistent startup code ###

echo "### RED HERRING ###"
[start adb here]

However one thing puzzles me: there is actually no grep in $PATH, so it's not clear to me why anything would expect it to work in the first place.