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commoncap: don't alloc the credential unless needed in cap_task_prctl

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In function cap_task_prctl(), we would allocate a credential
unconditionally and then check if we support the requested function.
If not we would release this credential with abort_creds() by using
RCU method. But on some archs such as powerpc, the sys_prctl is heavily
used to get/set the floating point exception mode. So the unnecessary
allocating/releasing of credential not only introduce runtime overhead
but also do cause OOM due to the RCU implementation.

This patch removes abort_creds() from cap_task_prctl() by calling
prepare_creds() only when we need to modify it.

Reported-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Paul Moore <paul@paul-moore.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.l.morris@oracle.com>
This commit is contained in:
Tetsuo Handa 2014-07-22 21:20:01 +09:00 committed by James Morris
parent fd33c43677
commit 6d6f332842
1 changed files with 30 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

72
security/commoncap.c
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@ -822,15 +822,20 @@ int cap_task_setnice(struct task_struct *p, int nice)
* Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from
* the current task's bounding set. Returns 0 on success, -ve on error.
*/
static long cap_prctl_drop(struct cred *new, unsigned long cap)
static int cap_prctl_drop(unsigned long cap)
{
struct cred *new;
if (!ns_capable(current_user_ns(), CAP_SETPCAP))
return -EPERM;
if (!cap_valid(cap))
return -EINVAL;
new = prepare_creds();
if (!new)
return -ENOMEM;
cap_lower(new->cap_bset, cap);
return 0;
return commit_creds(new);
}
/**
@ -848,26 +853,17 @@ static long cap_prctl_drop(struct cred *new, unsigned long cap)
int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
unsigned long arg4, unsigned long arg5)
{
const struct cred *old = current_cred();
struct cred *new;
long error = 0;
new = prepare_creds();
if (!new)
return -ENOMEM;
switch (option) {
case PR_CAPBSET_READ:
error = -EINVAL;
if (!cap_valid(arg2))
goto error;
error = !!cap_raised(new->cap_bset, arg2);
goto no_change;
return -EINVAL;
return !!cap_raised(old->cap_bset, arg2);
case PR_CAPBSET_DROP:
error = cap_prctl_drop(new, arg2);
if (error < 0)
goto error;
goto changed;
return cap_prctl_drop(arg2);
/*
* The next four prctl's remain to assist with transitioning a
@ -889,10 +885,9 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
* capability-based-privilege environment.
*/
case PR_SET_SECUREBITS:
error = -EPERM;
if ((((new->securebits & SECURE_ALL_LOCKS) >> 1)
& (new->securebits ^ arg2)) /*[1]*/
|| ((new->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
if ((((old->securebits & SECURE_ALL_LOCKS) >> 1)
& (old->securebits ^ arg2)) /*[1]*/
|| ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
|| (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
|| (cap_capable(current_cred(),
current_cred()->user_ns, CAP_SETPCAP,
@ -906,46 +901,39 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
*/
)
/* cannot change a locked bit */
goto error;
return -EPERM;
new = prepare_creds();
if (!new)
return -ENOMEM;
new->securebits = arg2;
goto changed;
return commit_creds(new);
case PR_GET_SECUREBITS:
error = new->securebits;
goto no_change;
return old->securebits;
case PR_GET_KEEPCAPS:
if (issecure(SECURE_KEEP_CAPS))
error = 1;
goto no_change;
return !!issecure(SECURE_KEEP_CAPS);
case PR_SET_KEEPCAPS:
error = -EINVAL;
if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */
goto error;
error = -EPERM;
return -EINVAL;
if (issecure(SECURE_KEEP_CAPS_LOCKED))
goto error;
return -EPERM;
new = prepare_creds();
if (!new)
return -ENOMEM;
if (arg2)
new->securebits |= issecure_mask(SECURE_KEEP_CAPS);
else
new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
goto changed;
return commit_creds(new);
default:
/* No functionality available - continue with default */
error = -ENOSYS;
goto error;
return -ENOSYS;
}
/* Functionality provided */
changed:
return commit_creds(new);
no_change:
error:
abort_creds(new);
return error;
}
/**