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system.3: Create a "Caveats" subsection to hold warnings about the use of system() 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2017-11-20 14:54:00 +01:00
parent 979a439b41
commit a6be81bab9
1 changed files with 21 additions and 19 deletions
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man3/system.3
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@ -174,25 +174,6 @@ while (something) {
.EE
.in
.PP
Do not use
.BR system ()
from a program with set-user-ID or set-group-ID privileges,
because strange values for some environment variables
might be used to subvert system integrity.
Use the
.BR exec (3)
family of functions instead, but not
.BR execlp (3)
or
.BR execvp (3).
.BR system ()
will not, in fact, work properly from programs with set-user-ID or
set-group-ID privileges on systems on which
.I /bin/sh
is bash version 2, since bash 2 drops privileges on startup.
(Debian uses a modified bash which does not do this when invoked as
.BR sh .)
.PP
According to POSIX.1, it is unspecified whether handlers registered using
.BR pthread_atfork (3)
are called during the execution of
@ -218,6 +199,27 @@ which yields a
.BR system ()
return value that is indistinguishable from the case
where a shell could not be executed in the child process.
.\"
.SS Caveats
.PP
Do not use
.BR system ()
from a program with set-user-ID or set-group-ID privileges,
because strange values for some environment variables
might be used to subvert system integrity.
Use the
.BR exec (3)
family of functions instead, but not
.BR execlp (3)
or
.BR execvp (3).
.BR system ()
will not, in fact, work properly from programs with set-user-ID or
set-group-ID privileges on systems on which
.I /bin/sh
is bash version 2, since bash 2 drops privileges on startup.
(Debian uses a modified bash which does not do this when invoked as
.BR sh .)
.SH SEE ALSO
.BR sh (1),
.BR execve (2),