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When exec'ing a set[ug]id program, make sure that the stdio file descriptors

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(0, 1, 2) are allocated by opening /dev/null for any which are not already
open.

Reviewed by:	alfred, phk
MFC after:	2 days
This commit is contained in:
Jacques Vidrine 2002-04-19 00:45:29 +00:00
parent 091a610ac9
commit e983a3762b
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=95017
3 changed files with 70 additions and 0 deletions
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65
sys/kern/kern_descrip.c
View File

@ -53,6 +53,7 @@
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/proc.h>
#include <sys/namei.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/filio.h>
@ -1497,6 +1498,70 @@ fdcloseexec(td)
FILEDESC_UNLOCK(fdp);
}
/*
* It is unsafe for set[ug]id processes to be started with file
* descriptors 0..2 closed, as these descriptors are given implicit
* significance in the Standard C library. fdcheckstd() will create a
* descriptor referencing /dev/null for each of stdin, stdout, and
* stderr that is not already open.
*/
int
fdcheckstd(td)
struct thread *td;
{
struct nameidata nd;
struct filedesc *fdp;
struct file *fp;
register_t retval;
int fd, i, error, flags, devnull;
fdp = td->td_proc->p_fd;
if (fdp == NULL)
return (0);
devnull = -1;
error = 0;
for (i = 0; i < 3; i++) {
if (fdp->fd_ofiles[i] != NULL)
continue;
if (devnull < 0) {
FILEDESC_LOCK(fdp);
error = falloc(td, &fp, &fd);
FILEDESC_UNLOCK(fdp);
if (error != 0)
break;
NDINIT(&nd, LOOKUP, FOLLOW, UIO_SYSSPACE, "/dev/null",
td);
flags = FREAD | FWRITE;
error = vn_open(&nd, &flags, 0);
if (error != 0) {
FILEDESC_LOCK(fdp);
fdp->fd_ofiles[i] = NULL;
FILEDESC_UNLOCK(fdp);
fdrop(fp, td);
break;
}
NDFREE(&nd, NDF_ONLY_PNBUF);
fp->f_data = (caddr_t)nd.ni_vp;
fp->f_flag = flags;
fp->f_ops = &vnops;
fp->f_type = DTYPE_VNODE;
VOP_UNLOCK(nd.ni_vp, 0, td);
devnull = fd;
} else {
FILEDESC_LOCK(fdp);
error = fdalloc(td, 0, &fd);
if (error != 0) {
FILEDESC_UNLOCK(fdp);
break;
}
error = do_dup(fdp, devnull, fd, &retval, td);
if (error != 0)
break;
}
}
return (error);
}
/*
* Internal form of close.
* Decrement reference count on file structure.

4
sys/kern/kern_exec.c
View File

@ -368,6 +368,10 @@ execve(td, uap)
vrele(vtmp);
}
}
/* Make sure file descriptors 0..2 are in use. */
error = fdcheckstd(td);
if (error != 0)
goto exec_fail_dealloc;
/*
* Set the new credentials.
*/

1
sys/sys/filedesc.h
View File

@ -147,6 +147,7 @@ int falloc(struct thread *p, struct file **resultfp, int *resultfd);
int fdalloc(struct thread *p, int want, int *result);
int fdavail(struct thread *td, int n);
void fdcloseexec(struct thread *td);
int fdcheckstd(struct thread *td);
struct filedesc *fdcopy(struct thread *td);
void fdfree(struct thread *td);
struct filedesc *fdinit(struct thread *td);