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cred: Add a light version of override/revert_creds()

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Add a light version of override/revert_creds(), this should only be
used when the credentials in question will outlive the critical
section and the critical section doesn't change the ->usage of the
credentials.

Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
This commit is contained in:
Vinicius Costa Gomes 2024-11-06 16:57:17 -08:00 committed by Amir Goldstein
parent 48b50624ae
commit 49dffdfde4
2 changed files with 21 additions and 3 deletions
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18
include/linux/cred.h
View File

@ -172,6 +172,24 @@ static inline bool cap_ambient_invariant_ok(const struct cred *cred)
cred->cap_inheritable)); cred->cap_inheritable));
} }
/*
* Override creds without bumping reference count. Caller must ensure
* reference remains valid or has taken reference. Almost always not the
* interface you want. Use override_creds()/revert_creds() instead.
*/
static inline const struct cred *override_creds_light(const struct cred *override_cred)
{
const struct cred *old = current->cred;
rcu_assign_pointer(current->cred, override_cred);
return old;
}
static inline void revert_creds_light(const struct cred *revert_cred)
{
rcu_assign_pointer(current->cred, revert_cred);
}
/** /**
* get_new_cred_many - Get references on a new set of credentials * get_new_cred_many - Get references on a new set of credentials
* @cred: The new credentials to reference * @cred: The new credentials to reference

6
kernel/cred.c
View File

@ -485,7 +485,7 @@ EXPORT_SYMBOL(abort_creds);
*/ */
const struct cred *override_creds(const struct cred *new) const struct cred *override_creds(const struct cred *new)
{ {
const struct cred *old = current->cred; const struct cred *old;
kdebug("override_creds(%p{%ld})", new, kdebug("override_creds(%p{%ld})", new,
atomic_long_read(&new->usage)); atomic_long_read(&new->usage));
@ -499,7 +499,7 @@ const struct cred *override_creds(const struct cred *new)
* visible to other threads under RCU. * visible to other threads under RCU.
*/ */
get_new_cred((struct cred *)new); get_new_cred((struct cred *)new);
rcu_assign_pointer(current->cred, new); old = override_creds_light(new);
kdebug("override_creds() = %p{%ld}", old, kdebug("override_creds() = %p{%ld}", old,
atomic_long_read(&old->usage)); atomic_long_read(&old->usage));
@ -521,7 +521,7 @@ void revert_creds(const struct cred *old)
kdebug("revert_creds(%p{%ld})", old, kdebug("revert_creds(%p{%ld})", old,
atomic_long_read(&old->usage)); atomic_long_read(&old->usage));
rcu_assign_pointer(current->cred, old); revert_creds_light(old);
put_cred(override); put_cred(override);
} }
EXPORT_SYMBOL(revert_creds); EXPORT_SYMBOL(revert_creds);