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linux(4) prctl(2): Implement PR_[GS]ET_DUMPABLE

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Proxy the flag to the roughly analogous FreeBSD procctl 'TRACE'.

TRACE-disabled processes are not coredumped, and Linux !DUMPABLE processes
can not be ptraced.  There are some additional semantics around ownership of
files in the /proc/[pid] pseudo-filesystem, which we do not attempt to
emulate correctly at this time.

Reviewed by:	markj (earlier version)
Differential Revision:	https://reviews.freebsd.org/D27015
This commit is contained in:
Conrad Meyer 2020-11-03 02:10:54 +00:00
parent 443d8a07df
commit eaa5afcefa
2 changed files with 46 additions and 4 deletions
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44
sys/compat/linux/linux_misc.c
View File

@ -1937,7 +1937,7 @@ linux_prctl(struct thread *td, struct linux_prctl_args *args)
int error = 0, max_size;
struct proc *p = td->td_proc;
char comm[LINUX_MAX_COMM_LEN];
int pdeath_signal;
int pdeath_signal, trace_state;
switch (args->option) {
case LINUX_PR_SET_PDEATHSIG:
@ -1955,10 +1955,46 @@ linux_prctl(struct thread *td, struct linux_prctl_args *args)
return (copyout(&pdeath_signal,
(void *)(register_t)args->arg2,
sizeof(pdeath_signal)));
/*
* In Linux, this flag controls if set[gu]id processes can coredump.
* There are additional semantics imposed on processes that cannot
* coredump:
* - Such processes can not be ptraced.
* - There are some semantics around ownership of process-related files
* in the /proc namespace.
*
* In FreeBSD, we can (and by default, do) disable setuid coredump
* system-wide with 'sugid_coredump.' We control tracability on a
* per-process basis with the procctl PROC_TRACE (=> P2_NOTRACE flag).
* By happy coincidence, P2_NOTRACE also prevents coredumping. So the
* procctl is roughly analogous to Linux's DUMPABLE.
*
* So, proxy these knobs to the corresponding PROC_TRACE setting.
*/
case LINUX_PR_GET_DUMPABLE:
error = kern_procctl(td, P_PID, p->p_pid, PROC_TRACE_STATUS,
&trace_state);
if (error != 0)
return (error);
td->td_retval[0] = (trace_state != -1);
return (0);
case LINUX_PR_SET_DUMPABLE:
linux_msg(td, "unsupported prctl PR_SET_DUMPABLE");
error = EINVAL;
break;
/*
* It is only valid for userspace to set one of these two
* flags, and only one at a time.
*/
switch (args->arg2) {
case LINUX_SUID_DUMP_DISABLE:
trace_state = PROC_TRACE_CTL_DISABLE_EXEC;
break;
case LINUX_SUID_DUMP_USER:
trace_state = PROC_TRACE_CTL_ENABLE;
break;
default:
return (EINVAL);
}
return (kern_procctl(td, P_PID, p->p_pid, PROC_TRACE_CTL,
&trace_state));
case LINUX_PR_GET_KEEPCAPS:
/*
* Indicate that we always clear the effective and

6
sys/compat/linux/linux_misc.h
View File

@ -50,6 +50,7 @@
* Second arg is a ptr to return the
* signal.
*/
#define LINUX_PR_GET_DUMPABLE 3
#define LINUX_PR_SET_DUMPABLE 4
#define LINUX_PR_GET_KEEPCAPS 7 /* Get drop capabilities on setuid */
#define LINUX_PR_SET_KEEPCAPS 8 /* Set drop capabilities on setuid */
@ -62,6 +63,11 @@
#define LINUX_MAX_COMM_LEN 16 /* Maximum length of the process name. */
/* For GET/SET DUMPABLE */
#define LINUX_SUID_DUMP_DISABLE 0 /* Don't coredump setuid processes. */
#define LINUX_SUID_DUMP_USER 1 /* Dump as user of process. */
#define LINUX_SUID_DUMP_ROOT 2 /* Dump as root. */
#define LINUX_MREMAP_MAYMOVE 1
#define LINUX_MREMAP_FIXED 2