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Keep CAP_SYS_PTRACE with suid binary #1043

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merged 2 commits into from
Jan 12, 2017
Merged

Keep CAP_SYS_PTRACE with suid binary #1043

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ea1313d
Keep CAP_SYS_PTRACE with suid binary
Hummer12007 Jan 12, 2017
d9ba61d
Log capability dropping
Hummer12007 Jan 12, 2017
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29 changes: 29 additions & 0 deletions sway/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,9 @@
#include <unistd.h>
#include <getopt.h>
#include <sys/capability.h>
#ifdef __linux__
#include <sys/prctl.h>
#endif
#include "sway/extensions.h"
#include "sway/layout.h"
#include "sway/config.h"
Expand Down Expand Up @@ -289,6 +292,18 @@ int main(int argc, char **argv) {
return 0;
}

#ifdef __linux__
bool suid = false;
if (getuid() != geteuid() || getgid() != getegid()) {
// Retain capabilities after setuid()
if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0)) {
sway_log(L_ERROR, "Cannot keep caps after setuid()");
exit(EXIT_FAILURE);
}
suid = true;
}
#endif

// we need to setup logging before wlc_init in case it fails.
if (debug) {
init_log(L_DEBUG);
Expand All @@ -311,6 +326,20 @@ int main(int argc, char **argv) {
}
register_extensions();

#ifdef __linux__
if (suid) {
// Drop every cap except CAP_SYS_PTRACE
cap_t caps = cap_init();
cap_value_t keep = CAP_SYS_PTRACE;
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Don't we also want that TTY one?

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No, it was required because a suid binary would not gain all caps as effective, and besides, all the privileged stuff is dealt with in a child process of wlc (forked in wlc_init, so it keeps everything), so it isn't.

sway_log(L_INFO, "Dropping extra capabilities");
if (cap_set_flag(caps, CAP_PERMITTED, 1, &keep, CAP_SET) ||
cap_set_flag(caps, CAP_EFFECTIVE, 1, &keep, CAP_SET) ||
cap_set_proc(caps)) {
sway_log(L_ERROR, "Failed to drop extra capabilities");
exit(EXIT_FAILURE);
}
}
#endif
// handle SIGTERM signals
signal(SIGTERM, sig_handler);

Expand Down