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.
>
> 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
>
