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When calculating arguments to the interpreter for the shebang script

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executed by fexecve(2), imgp->args->fname is NULL. Moreover, there is
no way to recover the path to the script being executed.
Do what some other U*ixes do unconditionally, namely supply /dev/fd/n
as the script path when called from fexecve(). Document requirement of
having fdescfs mounted as caveat.
This commit is contained in:
Konstantin Belousov 2008-08-26 10:53:32 +00:00
parent 321e12c82e
commit eaad109973
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=182191
2 changed files with 40 additions and 6 deletions
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19
lib/libc/sys/execve.2
View File

@ -314,7 +314,7 @@ The
.Fa fd
argument is not a valid file descriptor open for executing.
.El
.Sh CAVEAT
.Sh CAVEATS
If a program is
.Em setuid
to a non-super-user, but is executed when
@ -322,6 +322,22 @@ the real
.Em uid
is ``root'', then the program has some of the powers
of a super-user as well.
.Pp
When executing an interpreted program through
.Fn fexecve ,
kernel supplies
.Pa /dev/fd/n
as a second argument to the interpreter,
where
.Ar n
is the file descriptor passed in the
.Fa fd
argument to
.Fn fexecve .
For this construction to work correctly, the
.Xr fdescfs 5
filesystem shall be mounted on
.Pa /dev/fd .
.Sh SEE ALSO
.Xr ktrace 1 ,
.Xr _exit 2 ,
@ -332,6 +348,7 @@ of a super-user as well.
.Xr sysctl 3 ,
.Xr a.out 5 ,
.Xr elf 5 ,
.Xr fdescfs 5 ,
.Xr environ 7 ,
.Xr mount 8
.Sh STANDARDS

27
sys/kern/imgact_shell.c
View File

@ -30,6 +30,7 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/vnode.h>
#include <sys/proc.h>
#include <sys/sbuf.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/exec.h>
@ -95,10 +96,11 @@ exec_shell_imgact(imgp)
struct image_params *imgp;
{
const char *image_header = imgp->image_header;
const char *ihp, *interpb, *interpe, *maxp, *optb, *opte;
const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
int error, offset;
size_t length, clength;
struct vattr vattr;
struct sbuf *sname;
/* a shell script? */
if (((const short *) image_header)[0] != SHELLMAGIC)
@ -164,6 +166,16 @@ exec_shell_imgact(imgp)
while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
opte = ihp;
if (imgp->args->fname != NULL) {
fname = imgp->args->fname;
sname = NULL;
} else {
sname = sbuf_new_auto();
sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
sbuf_finish(sname);
fname = sbuf_data(sname);
}
/*
* We need to "pop" (remove) the present value of arg[0], and "push"
* either two or three new values in the arg[] list. To do this,
@ -175,12 +187,15 @@ exec_shell_imgact(imgp)
offset = interpe - interpb + 1; /* interpreter */
if (opte > optb) /* options (if any) */
offset += opte - optb + 1;
offset += strlen(imgp->args->fname) + 1; /* fname of script */
offset += strlen(fname) + 1; /* fname of script */
length = (imgp->args->argc == 0) ? 0 :
strlen(imgp->args->begin_argv) + 1; /* bytes to delete */
if (offset - length > imgp->args->stringspace)
if (offset - length > imgp->args->stringspace) {
if (sname != NULL)
sbuf_delete(sname);
return (E2BIG);
}
bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
imgp->args->endp - (imgp->args->begin_argv + length));
@ -221,13 +236,15 @@ exec_shell_imgact(imgp)
* use and copy the interpreter's name to imgp->interpreter_name
* for exec to use.
*/
error = copystr(imgp->args->fname, imgp->args->buf + offset,
imgp->args->stringspace, &length);
error = copystr(fname, imgp->args->buf + offset, imgp->args->stringspace,
&length);
if (error == 0)
error = copystr(imgp->args->begin_argv, imgp->interpreter_name,
MAXSHELLCMDLEN, &length);
if (sname != NULL)
sbuf_delete(sname);
return (error);
}