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session: Don't refuse unprivileged creation of "direct" backend

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When starting a compositor that's using the "direct" session backend,
wlroots needs to handle calls to `drmSetMaster()` and `drmDropMaster()`.
As both calls used to require `CAP_SYS_ADMIN`, wlroots thus simply
refused starting in case the process doesn't enjoy evelated privileges.

Permission rules have changed since linux.git commit 45bc3d26c95a (drm:
rework SET_MASTER and DROP_MASTER perm handling, 2020-03-19). As a
result, starting with Linux v5.8, both ioctls will now also succeed if
the process is currently or has been the DRM master. And as the first
process to open render nodes will become the DRM master automatically,
this effectively means that process elevation is not strictly required
in all setups anymore.

So let's drop the `geteuid() != 0` permission check to allow those new
rules to do their magic.
This commit is contained in:
Patrick Steinhardt 2020-09-03 21:25:33 +02:00 committed by Simon Ser
parent efe6414640
commit fa05d3cde6
1 changed files with 0 additions and 14 deletions
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14
backend/session/direct-ipc.c
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@ -24,16 +24,6 @@
enum { DRM_MAJOR = 226 }; enum { DRM_MAJOR = 226 };
static bool have_permissions(void) {
#ifdef __linux__
if (geteuid() != 0) {
wlr_log(WLR_ERROR, "Do not have root privileges; cannot become DRM master");
return false;
}
#endif
return true;
}
static void send_msg(int sock, int fd, void *buf, size_t buf_len) { static void send_msg(int sock, int fd, void *buf, size_t buf_len) {
char control[CMSG_SPACE(sizeof(fd))] = {0}; char control[CMSG_SPACE(sizeof(fd))] = {0};
struct iovec iovec = { .iov_base = buf, .iov_len = buf_len }; struct iovec iovec = { .iov_base = buf, .iov_len = buf_len };
@ -223,10 +213,6 @@ void direct_ipc_finish(int sock, pid_t pid) {
} }
int direct_ipc_init(pid_t *pid_out) { int direct_ipc_init(pid_t *pid_out) {
if (!have_permissions()) {
return -1;
}
int sock[2]; int sock[2];
if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sock) < 0) { if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sock) < 0) {
wlr_log_errno(WLR_ERROR, "Failed to create socket pair"); wlr_log_errno(WLR_ERROR, "Failed to create socket pair");