ptrace: Properly initialize ptracer_cred on fork
authorEric W. Biederman <ebiederm@xmission.com>
Mon, 22 May 2017 20:40:12 +0000 (15:40 -0500)
committerEric W. Biederman <ebiederm@xmission.com>
Tue, 23 May 2017 12:40:44 +0000 (07:40 -0500)
commitc70d9d809fdeecedb96972457ee45c49a232d97f
treed814992a6f46fdc1b9faac491aaa30744cb2ed57
parent3fd37226216620c1a468afa999739d5016fbc349
ptrace: Properly initialize ptracer_cred on fork

When I introduced ptracer_cred I failed to consider the weirdness of
fork where the task_struct copies the old value by default.  This
winds up leaving ptracer_cred set even when a process forks and
the child process does not wind up being ptraced.

Because ptracer_cred is not set on non-ptraced processes whose
parents were ptraced this has broken the ability of the enlightenment
window manager to start setuid children.

Fix this by properly initializing ptracer_cred in ptrace_init_task

This must be done with a little bit of care to preserve the current value
of ptracer_cred when ptrace carries through fork.  Re-reading the
ptracer_cred from the ptracing process at this point is inconsistent
with how PT_PTRACE_CAP has been maintained all of these years.

Tested-by: Takashi Iwai <tiwai@suse.de>
Fixes: 64b875f7ac8a ("ptrace: Capture the ptracer's creds not PT_PTRACE_CAP")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
include/linux/ptrace.h
kernel/ptrace.c