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security: keys: perform capable check only on privileged operations

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If the current task fails the check for the queried capability via
`capable(CAP_SYS_ADMIN)` LSMs like SELinux generate a denial message.
Issuing such denial messages unnecessarily can lead to a policy author
granting more privileges to a subject than needed to silence them.

Reorder CAP_SYS_ADMIN checks after the check whether the operation is
actually privileged.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
This commit is contained in:
Christian Göttsche 2023-05-11 14:32:52 +02:00 committed by Jarkko Sakkinen
parent 57012c5753
commit 2d7f105edb
1 changed files with 8 additions and 3 deletions
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11
security/keys/keyctl.c
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@ -980,14 +980,19 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
ret = -EACCES;
down_write(&key->sem);
if (!capable(CAP_SYS_ADMIN)) {
{
bool is_privileged_op = false;
/* only the sysadmin can chown a key to some other UID */
if (user != (uid_t) -1 && !uid_eq(key->uid, uid))
goto error_put;
is_privileged_op = true;
/* only the sysadmin can set the key's GID to a group other
* than one of those that the current process subscribes to */
if (group != (gid_t) -1 && !gid_eq(gid, key->gid) && !in_group_p(gid))
is_privileged_op = true;
if (is_privileged_op && !capable(CAP_SYS_ADMIN))
goto error_put;
}
@ -1088,7 +1093,7 @@ long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
down_write(&key->sem);
/* if we're not the sysadmin, we can only change a key that we own */
if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid())) {
if (uid_eq(key->uid, current_fsuid()) || capable(CAP_SYS_ADMIN)) {
key->perm = perm;
notify_key(key, NOTIFY_KEY_SETATTR, 0);
ret = 0;