On Tue, 10 Jan 2023 at 14:18, Stephen Smalley
<stephen.smalley.work@xxxxxxxxx> wrote:
>
> On Mon, Jan 9, 2023 at 12:17 PM Christian Göttsche
> <cgzones@xxxxxxxxxxxxxx> wrote:
> >
> > Add the public interfaces getpidprevcon(3) and getpidprevcon_raw(3), and
> > the utility getpidprevcon to gather the previous context before the last
> > exec of a given process.
>
> Wondering if we should warn in the manual page for this and other
> getpid*con() interfaces that they are inherently racy and therefore
> should never be relied upon for security purposes.
With "and other getpid*con() interfaces" do you mean just getpidcon(3)
(and getpidcon_raw(3)), which is currently the only interface matching
your regex and operating on a foreign process, or also getcon(3) and
getprevcon(3)?
With race conditions you mean the possibility of the target process
changing its context (via setcon(3)) or querying a replaced process
(which is mainly possible via spawning a new process after setting
/proc/sys/kernel/ns_last_pid)?
Or do you have others in mind?
p.s.:
after the discussion has settled I'll send a v2 with the interfaces
actually published in libselinux.map
> >
> > Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
> > ---
> > libselinux/include/selinux/selinux.h | 5 ++++
> > libselinux/man/man3/getcon.3 | 9 +++++++
> > libselinux/man/man3/getpidprevcon.3 | 1 +
> > libselinux/man/man3/getpidprevcon_raw.3 | 1 +
> > libselinux/src/procattr.c | 18 ++++++++++++++
> > libselinux/utils/.gitignore | 1 +
> > libselinux/utils/getpidprevcon.c | 33 +++++++++++++++++++++++++
> > 7 files changed, 68 insertions(+)
> > create mode 100644 libselinux/man/man3/getpidprevcon.3
> > create mode 100644 libselinux/man/man3/getpidprevcon_raw.3
> > create mode 100644 libselinux/utils/getpidprevcon.c
> >
> > diff --git a/libselinux/include/selinux/selinux.h b/libselinux/include/selinux/selinux.h
> > index 47af9953..a0948853 100644
> > --- a/libselinux/include/selinux/selinux.h
> > +++ b/libselinux/include/selinux/selinux.h
> > @@ -54,6 +54,11 @@ extern int getpidcon_raw(pid_t pid, char ** con);
> > extern int getprevcon(char ** con);
> > extern int getprevcon_raw(char ** con);
> >
> > +/* Get previous context (prior to last exec) of process identified by pid, and
> > + set *con to refer to it. Caller must free via freecon. */
> > +extern int getpidprevcon(pid_t pid, char ** con);
> > +extern int getpidprevcon_raw(pid_t pid, char ** con);
> > +
> > /* Get exec context, and set *con to refer to it.
> > Sets *con to NULL if no exec context has been set, i.e. using default.
> > If non-NULL, caller must free via freecon. */
> > diff --git a/libselinux/man/man3/getcon.3 b/libselinux/man/man3/getcon.3
> > index e7e394f3..38da958b 100644
> > --- a/libselinux/man/man3/getcon.3
> > +++ b/libselinux/man/man3/getcon.3
> > @@ -23,6 +23,10 @@ setcon \- set current security context of a process
> > .sp
> > .BI "int getpidcon_raw(pid_t " pid ", char **" context );
> > .sp
> > +.BI "int getpidprevcon(pid_t " pid ", char **" context );
> > +.sp
> > +.BI "int getpidprevcon_raw(pid_t " pid ", char **" context );
> > +.sp
> > .BI "int getpeercon(int " fd ", char **" context );
> > .sp
> > .BI "int getpeercon_raw(int " fd ", char **" context );
> > @@ -50,6 +54,11 @@ same as getcon but gets the context before the last exec.
> > returns the process context for the specified PID, which must be free'd with
> > .BR freecon ().
> >
> > +.TP
> > +.BR getpidprevcon ()
> > +returns the process context before the last exec for the specified PID, which must be free'd with
> > +.BR freecon ().
> > +
> > .TP
> > .BR getpeercon ()
> > retrieves the context of the peer socket, which must be free'd with
> > diff --git a/libselinux/man/man3/getpidprevcon.3 b/libselinux/man/man3/getpidprevcon.3
> > new file mode 100644
> > index 00000000..1210b5a0
> > --- /dev/null
> > +++ b/libselinux/man/man3/getpidprevcon.3
> > @@ -0,0 +1 @@
> > +.so man3/getcon.3
> > diff --git a/libselinux/man/man3/getpidprevcon_raw.3 b/libselinux/man/man3/getpidprevcon_raw.3
> > new file mode 100644
> > index 00000000..1210b5a0
> > --- /dev/null
> > +++ b/libselinux/man/man3/getpidprevcon_raw.3
> > @@ -0,0 +1 @@
> > +.so man3/getcon.3
> > diff --git a/libselinux/src/procattr.c b/libselinux/src/procattr.c
> > index 6f4cfb82..b7a93a2b 100644
> > --- a/libselinux/src/procattr.c
> > +++ b/libselinux/src/procattr.c
> > @@ -300,3 +300,21 @@ int getpidcon(pid_t pid, char **c)
> > }
> > return getprocattrcon(c, pid, "current", NULL);
> > }
> > +
> > +int getpidprevcon_raw(pid_t pid, char **c)
> > +{
> > + if (pid <= 0) {
> > + errno = EINVAL;
> > + return -1;
> > + }
> > + return getprocattrcon_raw(c, pid, "prev", NULL);
> > +}
> > +
> > +int getpidprevcon(pid_t pid, char **c)
> > +{
> > + if (pid <= 0) {
> > + errno = EINVAL;
> > + return -1;
> > + }
> > + return getprocattrcon(c, pid, "prev", NULL);
> > +}
> > diff --git a/libselinux/utils/.gitignore b/libselinux/utils/.gitignore
> > index 3ef34374..b19b94a8 100644
> > --- a/libselinux/utils/.gitignore
> > +++ b/libselinux/utils/.gitignore
> > @@ -9,6 +9,7 @@ getdefaultcon
> > getenforce
> > getfilecon
> > getpidcon
> > +getpidprevcon
> > getsebool
> > getseuser
> > matchpathcon
> > diff --git a/libselinux/utils/getpidprevcon.c b/libselinux/utils/getpidprevcon.c
> > new file mode 100644
> > index 00000000..662ad500
> > --- /dev/null
> > +++ b/libselinux/utils/getpidprevcon.c
> > @@ -0,0 +1,33 @@
> > +#include <unistd.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <errno.h>
> > +#include <selinux/selinux.h>
> > +
> > +int main(int argc, char **argv)
> > +{
> > + pid_t pid;
> > + char *buf;
> > + int rc;
> > +
> > + if (argc != 2) {
> > + fprintf(stderr, "usage: %s pid\n", argv[0]);
> > + exit(1);
> > + }
> > +
> > + if (sscanf(argv[1], "%d", &pid) != 1) {
> > + fprintf(stderr, "%s: invalid pid %s\n", argv[0], argv[1]);
> > + exit(2);
> > + }
> > +
> > + rc = getpidprevcon(pid, &buf);
> > + if (rc < 0) {
> > + fprintf(stderr, "%s: getpidprevcon() failed: %s\n", argv[0], strerror(errno));
> > + exit(3);
> > + }
> > +
> > + printf("%s\n", buf);
> > + freecon(buf);
> > + exit(EXIT_SUCCESS);
> > +}
> > --
> > 2.39.0
> >
