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Smack: ignore null signal in smack_task_kill

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Kill with signal number 0 is commonly used for checking PID existence.
Smack treated such cases like any other kills, although no signal is
actually delivered when sig == 0.

Checking permissions when sig == 0 didn't prevent an unprivileged caller
from learning whether PID exists or not. When it existed, kernel returned
EPERM, when it didn't - ESRCH. The only effect of policy check in such
case is noise in audit logs.

This change lets Smack silently ignore kill() invocations with sig == 0.

Signed-off-by: Rafal Krypa <r.krypa@samsung.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
This commit is contained in:
Rafal Krypa 2016-04-04 11:14:53 +02:00 committed by Casey Schaufler
parent 40d273782f
commit 18d872f77c
1 changed files with 3 additions and 0 deletions
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3
security/smack/smack_lsm.c
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@ -2227,6 +2227,9 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
struct smack_known *tkp = smk_of_task_struct(p);
int rc;
if (!sig)
return 0; /* null signal; existence test */
smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
smk_ad_setfield_u_tsk(&ad, p);
/*