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selinux: fix empty write to keycreate file

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When sid == 0 (we are resetting keycreate_sid to the default value), we
should skip the KEY__CREATE check.

Before this patch, doing a zero-sized write to /proc/self/keycreate
would check if the current task can create unlabeled keys (which would
usually fail with -EACCESS and generate an AVC). Now it skips the check
and correctly sets the task's keycreate_sid to 0.

Bug report: https://bugzilla.redhat.com/show_bug.cgi?id=1719067

Tested using the reproducer from the report above.

Fixes: 4eb582cf1f ("[PATCH] keys: add a way to store the appropriate context for newly-created keys")
Reported-by: Kir Kolyshkin <kir@sacred.ru>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Ondrej Mosnacek 2019-06-12 10:12:26 +02:00 committed by Paul Moore
parent beee56f354
commit 464c258aa4
1 changed files with 6 additions and 5 deletions
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11
security/selinux/hooks.c
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@ -6331,11 +6331,12 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
} else if (!strcmp(name, "fscreate")) {
tsec->create_sid = sid;
} else if (!strcmp(name, "keycreate")) {
error = avc_has_perm(&selinux_state,
mysid, sid, SECCLASS_KEY, KEY__CREATE,
NULL);
if (error)
goto abort_change;
if (sid) {
error = avc_has_perm(&selinux_state, mysid, sid,
SECCLASS_KEY, KEY__CREATE, NULL);
if (error)
goto abort_change;
}
tsec->keycreate_sid = sid;
} else if (!strcmp(name, "sockcreate")) {
tsec->sockcreate_sid = sid;