Re: what happens if
2012/3/20 Diego Iastrubni elc...@kde.org On יום שלישי 20 מרץ 2012 10:45:19 Erez D wrote: All theory I read before implementing this said this was a bad idea. The theory says that libc may maintain some mutex inside malloc() which is called from printf() for example. This means that even trivial things may kill your app. The theory says that in multithreaded applications as soon as you clone() (the system called used by pthread_create()) you should execvp. In my application (a lot of C++, running on linux 2.6.32, glibc 2.9 and glibc 2.11.1 on ARM) erverything worked perfectly against the theory, your mileage may vary. what do you mean by erverything worked perfectly against the theory - did it work or did you have problems although you just execvp after clone ? Sorry, to be clear: I cloned(), then forked(), but no exec*() was called in the new child process. doesn't clone() and fork() do similar things ? why fork() after clone() ? Everything worked fine in my setup. But again, YMMV. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
2012/3/19 Diego Iastrubni elc...@kde.org On יום שני 19 מרץ 2012 12:22:15 Erez D wrote: On Mon, Mar 19, 2012 at 12:20 PM, Nadav Har'El n...@math.technion.ac.ilwrote: On Mon, Mar 19, 2012, Erez D wrote about Re: what happens if: my reason for fork is only for exec() - to protect the first program from the other. Then you should be all fine. Another reason is for interacting with libraries which are singleton. I had to work with a library to talk to some special HW. The library was designed to work with one device per process, and I needed to support many. I found myself forking and using pipe() to use the API from my main app. The problem is that that fork() was called from a thread. Read ahead. If you're talking about the C language, you won't have any of these problems. System calls like close() or dup() do not use any pthread capabilities like mutexes. If you're talking about a different programming language, I frankly have no idea what its fork() does. Maybe you need to write some C code that does fork()/exec() in one function call, and avoid this risk. i will be using C++. are you sure this is safe ? All theory I read before implementing this said this was a bad idea. The theory says that libc may maintain some mutex inside malloc() which is called from printf() for example. This means that even trivial things may kill your app. The theory says that in multithreaded applications as soon as you clone() (the system called used by pthread_create()) you should execvp. In my application (a lot of C++, running on linux 2.6.32, glibc 2.9 and glibc 2.11.1 on ARM) erverything worked perfectly against the theory, your mileage may vary. what do you mean by erverything worked perfectly against the theory - did it work or did you have problems although you just execvp after clone ? ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On יום שלישי 20 מרץ 2012 10:45:19 Erez D wrote: All theory I read before implementing this said this was a bad idea. The theory says that libc may maintain some mutex inside malloc() which is called from printf() for example. This means that even trivial things may kill your app. The theory says that in multithreaded applications as soon as you clone() (the system called used by pthread_create()) you should execvp. In my application (a lot of C++, running on linux 2.6.32, glibc 2.9 and glibc 2.11.1 on ARM) erverything worked perfectly against the theory, your mileage may vary. what do you mean by erverything worked perfectly against the theory - did it work or did you have problems although you just execvp after clone ? Sorry, to be clear: I cloned(), then forked(), but no exec*() was called in the new child process. Everything worked fine in my setup. But again, YMMV. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
what happens if
what happens if i am running a multithreaded app ( 3 threads ) and one thread calls fork() ? ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
Hi Erez,
On Mon, Mar 19, 2012 at 10:47:20AM +0200, Erez D wrote:
what happens if i am running a multithreaded app ( 3 threads ) and one
thread calls fork() ?
See pthread_atfork(3).
baruch
--
http://baruch.siach.name/blog/ ~. .~ Tk Open Systems
=}ooO--U--Ooo{=
- bar...@tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -
___
Linux-il mailing list
Linux-il@cs.huji.ac.il
http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
FTFM: The child process is created with a single thread - the one that called fork(). 2012/3/19 Erez D erez0...@gmail.com what happens if i am running a multithreaded app ( 3 threads ) and one thread calls fork() ? ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il -- Ubi dubium, ibi libertas (where there is doubt, there is freedom) ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On Mon, Mar 19, 2012, Erez D wrote about what happens if: what happens if i am running a multithreaded app ( 3 threads ) and one thread calls fork() ? On Linux, the new process will run ONLY a copy of the thread doing the fork(). The other threads are *not* copied to the child process. There is no way in Linux to ask to duplicate all of the process's threads, as in Solaris's forkall(2) system call. Even if such a system call existed, its usefulness would be dubious as explained in Posix's fork(2) manual: http://pubs.opengroup.org/onlinepubs/009695399/functions/fork.html (look for the section starting in The addition of the forkall() function to the standard was considered and rejected.) All this makes fork() more or less useless for multithreaded applications except for one idiom: fork() followed by exec(). -- Nadav Har'El|Monday, Mar 19 2012, n...@math.technion.ac.il |- Phone +972-523-790466, ICQ 13349191 |This space is for sale - inquire inside. http://nadav.harel.org.il | ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On Mon, Mar 19, 2012 at 11:40 AM, Nadav Har'El n...@math.technion.ac.ilwrote: On Mon, Mar 19, 2012, Erez D wrote about what happens if: what happens if i am running a multithreaded app ( 3 threads ) and one thread calls fork() ? On Linux, the new process will run ONLY a copy of the thread doing the fork(). The other threads are *not* copied to the child process. There is no way in Linux to ask to duplicate all of the process's threads, as in Solaris's forkall(2) system call. Even if such a system call existed, its usefulness would be dubious as explained in Posix's fork(2) manual: http://pubs.opengroup.org/onlinepubs/009695399/functions/fork.html (look for the section starting in The addition of the forkall() function to the standard was considered and rejected.) All this makes fork() more or less useless for multithreaded applications except for one idiom: fork() followed by exec(). my reason for fork is only for exec() - to protect the first program from the other. the problem that may arise in forking a multithreaded is that one thread may lock a mutex and then another call for fork, which means that the child inherits the locked mutex. i do not know internaly what library function use this mutex, e.g. will close() need this mutex ? will dup() will ? in this case, trying to close a side of a pipe, duping it or even closing open fds (for security issues) may hang the child while the library waits for the mutex , and no other thread exists in the child to release it a only way to resolve it, is to fork to another process before generating the other threads, the second process will be left single threaded and so may fork() with no problems, but this way i can't use pipe(), and need to revert to named pipe which is ugly any pther ideas ? things i missed ? -- Nadav Har'El|Monday, Mar 19 2012, n...@math.technion.ac.il |- Phone +972-523-790466, ICQ 13349191 |This space is for sale - inquire inside. http://nadav.harel.org.il | ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On Mon, Mar 19, 2012, Erez D wrote about Re: what happens if: my reason for fork is only for exec() - to protect the first program from the other. Then you should be all fine. the problem that may arise in forking a multithreaded is that one thread may lock a mutex and then another call for fork, which means that the child inherits the locked mutex. i do not know internaly what library function use this mutex, e.g. will close() need this mutex ? will dup() will ? in this case, trying to close a side of a pipe, duping it or even closing open fds (for security issues) may hang the child while the library waits for the mutex , and no other thread exists in the child to release it If you're talking about the C language, you won't have any of these problems. System calls like close() or dup() do not use any pthread capabilities like mutexes. If you're talking about a different programming language, I frankly have no idea what its fork() does. Maybe you need to write some C code that does fork()/exec() in one function call, and avoid this risk. Did actually notice any problem with your code, or is this question just theoretical? -- Nadav Har'El|Monday, Mar 19 2012, n...@math.technion.ac.il |- Phone +972-523-790466, ICQ 13349191 |If God had intended us to be vegetarians, http://nadav.harel.org.il |He wouldn't have made animals out of meat ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On Mon, Mar 19, 2012 at 12:20 PM, Nadav Har'El n...@math.technion.ac.ilwrote: On Mon, Mar 19, 2012, Erez D wrote about Re: what happens if: my reason for fork is only for exec() - to protect the first program from the other. Then you should be all fine. the problem that may arise in forking a multithreaded is that one thread may lock a mutex and then another call for fork, which means that the child inherits the locked mutex. i do not know internaly what library function use this mutex, e.g. will close() need this mutex ? will dup() will ? in this case, trying to close a side of a pipe, duping it or even closing open fds (for security issues) may hang the child while the library waits for the mutex , and no other thread exists in the child to release it If you're talking about the C language, you won't have any of these problems. System calls like close() or dup() do not use any pthread capabilities like mutexes. If you're talking about a different programming language, I frankly have no idea what its fork() does. Maybe you need to write some C code that does fork()/exec() in one function call, and avoid this risk. i will be using C++. are you sure this is safe ? Did actually notice any problem with your code, or is this question just theoretical? theoretical -- Nadav Har'El|Monday, Mar 19 2012, n...@math.technion.ac.il |- Phone +972-523-790466, ICQ 13349191 |If God had intended us to be vegetarians, http://nadav.harel.org.il |He wouldn't have made animals out of meat ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On Mon, Mar 19, 2012, Erez D wrote about Re: what happens if: If you're talking about the C language, you won't have any of these problems. System calls like close() or dup() do not use any pthread capabilities like mutexes. .. i will be using C++. are you sure this is safe ? I'm sure. But don't sue me if I'm wrong ;-) -- Nadav Har'El|Monday, Mar 19 2012, n...@math.technion.ac.il |- Phone +972-523-790466, ICQ 13349191 |Disclaimer: The opinions expressed above http://nadav.harel.org.il |are not my own. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On Mon, Mar 19, 2012 at 12:25 PM, Nadav Har'El n...@math.technion.ac.ilwrote: On Mon, Mar 19, 2012, Erez D wrote about Re: what happens if: If you're talking about the C language, you won't have any of these problems. System calls like close() or dup() do not use any pthread capabilities like mutexes. .. i will be using C++. are you sure this is safe ? I'm sure. But don't sue me if I'm wrong ;-) I wont thanks -- Nadav Har'El|Monday, Mar 19 2012, n...@math.technion.ac.il |- Phone +972-523-790466, ICQ 13349191 |Disclaimer: The opinions expressed above http://nadav.harel.org.il |are not my own. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: what happens if
On יום שני 19 מרץ 2012 12:22:15 Erez D wrote: On Mon, Mar 19, 2012 at 12:20 PM, Nadav Har'El n...@math.technion.ac.ilwrote: On Mon, Mar 19, 2012, Erez D wrote about Re: what happens if: my reason for fork is only for exec() - to protect the first program from the other. Then you should be all fine. Another reason is for interacting with libraries which are singleton. I had to work with a library to talk to some special HW. The library was designed to work with one device per process, and I needed to support many. I found myself forking and using pipe() to use the API from my main app. The problem is that that fork() was called from a thread. Read ahead. If you're talking about the C language, you won't have any of these problems. System calls like close() or dup() do not use any pthread capabilities like mutexes. If you're talking about a different programming language, I frankly have no idea what its fork() does. Maybe you need to write some C code that does fork()/exec() in one function call, and avoid this risk. i will be using C++. are you sure this is safe ? All theory I read before implementing this said this was a bad idea. The theory says that libc may maintain some mutex inside malloc() which is called from printf() for example. This means that even trivial things may kill your app. The theory says that in multithreaded applications as soon as you clone() (the system called used by pthread_create()) you should execvp. In my application (a lot of C++, running on linux 2.6.32, glibc 2.9 and glibc 2.11.1 on ARM) erverything worked perfectly against the theory, your mileage may vary. ___ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
On Thu, Mar 20, 2008 at 07:25:19PM +0200, Shachar Shemesh wrote: Valery Reznic wrote: Below is important part If the header of a file isn?t recognized (the attempted execve(2) returned ENOEXEC), these functions will execute the shell (/bin/sh) with the path of the file as its first argument. (If this attempt fails, no further searching is done.) Yes, I do believe you nailed it. After Matan's email I tried running the set with strace, and realized it was, indeed, a user space thing. As I need that for a (user space) program that intercepts the actual kernel calls (and sometimes emulates them), I will assume that the governing rule is that a program can have just one shell script in its interpreter path. And now to a slightly related subject - does anyone know how I can change the command line that appears in ps for a program after it has been run? I know it should be possible, because I vaguely remember programs that receive sensitive information in command line and try to immediately hide it, but merely writing to the argv addresses did not bring the desired results, and /proc/self/cmdline seems to be read only. I happenned to stumble on this question recently. prctl(2) has PR_SET_NAME. An even simpler solution, that may work on non-Linux too and may be good enough, is softlink. -- Dan Kenigsberghttp://www.cs.technion.ac.il/~dankenICQ 162180901 = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
Dan Kenigsberg wrote: I happenned to stumble on this question recently. prctl(2) has PR_SET_NAME. An even simpler solution, that may work on non-Linux too and may be good enough, is softlink. From the prctl man page: CONFORMING TO This call is Linux-specific. IRIX has a prctl() system call (also introduced in Linux 2.1.44 as irix_prctl on the MIPS architecture), with pro- totype So, it seems that writing to the argv buffer may, actually, be more platform indep than the alternative. Shachar = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Kernel question - what happens when a shell script is the interpreter for another shell script?
Hi all, I tried the following experiment. /tmp/file1 (marked executable) has the following content: #!/bin/date echo $@ /tmp/file2 has the following content: #!/tmp/file1 echo File2 when I run file2, I expect it to print out the current date. Instead, it prints out File2. In other words, it goes to /bin/sh to execute. I tried going over the kernel code that handles this, but I must be looking at the wrong place. I got as far as the function load_script (fs/binfmt_script.c line 18 in the 2.6.23 kernel code), which seems to go over the file, extract the interpreter, and restart the entire process. Of course, once the process has restarted, bprm-sh_bang is not zero (line 25 of the file), and the function returns ENOEXEC. This explains why a shell script cannot be the interpreter for a shell script. What is not explained, however, is what does happen. I have not been able to locate what happens when the kernel runs out of functions that may make sense of the file we try to execute (aside from returning ENOEXEC, which does not seem to be what is actually happening). I have also been unable to locate where in the source there is any special casing of /bin/sh (aside from when the kernel cannot find /sbin/init, /etc/init and /bin/init during boot). What's going on here? Shachar = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
Did you add /tmp/file1 to the list in /etc/shells? On Thu, 2008-03-20 at 16:23 +0200, Shachar Shemesh wrote: Hi all, I tried the following experiment. /tmp/file1 (marked executable) has the following content: #!/bin/date echo $@ /tmp/file2 has the following content: #!/tmp/file1 echo File2 when I run file2, I expect it to print out the current date. Instead, it prints out File2. In other words, it goes to /bin/sh to execute. -- MS-Windows is the Pal-Kal of the PC world. My own blog is at http://www.zak.co.il/tddpirate/ My opinions, as expressed in this E-mail message, are mine alone. They do not represent the official policy of any organization with which I may be affiliated in any way. WARNING TO SPAMMERS: at http://www.zak.co.il/spamwarning.html = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
On Thu, 20 Mar 2008, Shachar Shemesh wrote: Hi all, I tried the following experiment. /tmp/file1 (marked executable) has the following content: #!/bin/date echo $@ /tmp/file2 has the following content: #!/tmp/file1 echo File2 when I run file2, I expect it to print out the current date. Instead, it Why? Does that happen when you run /tmp/file1? prints out File2. In other words, it goes to /bin/sh to execute. Try replacing echo with sleep 60, and run pstree in another shell. Try running /tmp/file2 from zsh instead of bash (or tcsh). This will give you a clue about which source you need to scrutinize. -- Matan Ziv-Av. [EMAIL PROTECTED] = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
Hi, Shachar.
You look at correct place and got everything right.
Almost. OK, everything you look kernel side is OK.
When you run program from the shell, shell use
not execve, but execvp (or execlp)
from the man execve
===
Special semantics for execlp() and execvp()
The functions execlp() and execvp() will
duplicate the actions of the
shell in searching for an executable file if
the specified filename
does not contain a slash (/) character. The
search path is the path
specified in the environment by the PATH
variable. If this variable
isnt specified, the default path
:/bin:/usr/bin is used. In addi-
tion, certain errors are treated specially.
If permission is denied for a file (the
attempted execve(2) returned
EACCES), these functions will continue
searching the rest of the search
path. If no other file is found, however, they
will return with the
global variable errno set to EACCES.
Below is important part
If the header of a file isnt recognized
(the attempted execve(2)
returned ENOEXEC), these functions will
execute the shell (/bin/sh)
with the path of the file as its first
argument. (If this attempt
fails, no further searching is done.)
===
If you use compile program
#include stdlib.h
int main(int argc, char *argv[], char *envp[])
{
execve(argv[1], argv[1], envp);
}
and run it under strace
strace program /tmp/file2
You'll see, that execve return ENOEXEC, as it should
(and as you saw in the kernel sources)
Regards,
Valery.
--- Shachar Shemesh [EMAIL PROTECTED] wrote:
Hi all,
I tried the following experiment. /tmp/file1 (marked
executable) has the
following content:
#!/bin/date
echo $@
/tmp/file2 has the following content:
#!/tmp/file1
echo File2
when I run file2, I expect it to print out the
current date. Instead, it
prints out File2. In other words, it goes to
/bin/sh to execute.
I tried going over the kernel code that handles
this, but I must be
looking at the wrong place. I got as far as the
function load_script
(fs/binfmt_script.c line 18 in the 2.6.23 kernel
code), which seems to
go over the file, extract the interpreter, and
restart the entire
process. Of course, once the process has restarted,
bprm-sh_bang is not
zero (line 25 of the file), and the function returns
ENOEXEC. This
explains why a shell script cannot be the
interpreter for a shell script.
What is not explained, however, is what does happen.
I have not been
able to locate what happens when the kernel runs out
of functions that
may make sense of the file we try to execute (aside
from returning
ENOEXEC, which does not seem to be what is actually
happening). I have
also been unable to locate where in the source there
is any special
casing of /bin/sh (aside from when the kernel cannot
find /sbin/init,
/etc/init and /bin/init during boot).
What's going on here?
Shachar
=
To unsubscribe, send mail to
[EMAIL PROTECTED] with
the word unsubscribe in the message body, e.g.,
run the command
echo unsubscribe | mail
[EMAIL PROTECTED]
Be a better friend, newshound, and
know-it-all with Yahoo! Mobile. Try it now.
http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
=
To unsubscribe, send mail to [EMAIL PROTECTED] with
the word unsubscribe in the message body, e.g., run the command
echo unsubscribe | mail [EMAIL PROTECTED]
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
Valery Reznic wrote: Below is important part If the header of a file isn’t recognized (the attempted execve(2) returned ENOEXEC), these functions will execute the shell (/bin/sh) with the path of the file as its first argument. (If this attempt fails, no further searching is done.) Yes, I do believe you nailed it. After Matan's email I tried running the set with strace, and realized it was, indeed, a user space thing. As I need that for a (user space) program that intercepts the actual kernel calls (and sometimes emulates them), I will assume that the governing rule is that a program can have just one shell script in its interpreter path. And now to a slightly related subject - does anyone know how I can change the command line that appears in ps for a program after it has been run? I know it should be possible, because I vaguely remember programs that receive sensitive information in command line and try to immediately hide it, but merely writing to the argv addresses did not bring the desired results, and /proc/self/cmdline seems to be read only. Shachar To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Kernel question - what happens when a shell script is the interpreter for another shell script?
On Thu, Mar 20, 2008 at 07:25:19PM +0200, Shachar Shemesh wrote: And now to a slightly related subject - does anyone know how I can change the command line that appears in ps for a program after it has been run? I know it should be possible, because I vaguely remember programs that receive sensitive information in command line and try to immediately hide it, but merely writing to the argv addresses did not bring the desired results, Are you sure? This works for me: strncpy(argv[0], test123 456, strlen(argv[0])); But this doesn't: argv[0] = test123 456; Make sure you get it right. -- Didi = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
set what happens when I do poweroff
Hello guys.. Sorry for all of the questions... I would like to know if I can set whats happening when I do "poweroff" or "halt" or "shutdown -h now" I thought maby I should reconfigure something there to fix the Power off thing... Cause apm is working great at my PC... If I do "apm --standby" for example, it's moving to a standby position... So I would like to know if I can change the proccess of the shutdown... Thanks, David = To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
