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Message-ID: <a9588785-e03a-4a25-9172-045d3857d046@canonical.com>
Date: Sat, 17 May 2025 18:35:32 -0700
From: John Johansen <john.johansen@...onical.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: paul@...l-moore.com, linux-kernel@...r.kernel.org,
apparmor@...ts.ubuntu.com, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] apparmor: make __begin_current_label_crit_section()
indicate whether put is needed
On 3/18/25 15:06, Mateusz Guzik wrote:
> Same as aa_get_newest_cred_label_condref().
>
> This avoids a bunch of work overall and allows the compiler to note when no
> clean up is necessary, allowing for tail calls.
>
> This in particular happens in apparmor_file_permission(), which manages to
> tail call aa_file_perm() 105 bytes in (vs a regular call 112 bytes in
> followed by branches to figure out if clean up is needed).
>
do we have any numbers on the difference? And why not also the none underscore
versions. ie. begin_current_XXX and end_current_XXX. Admittedly they can sleep
an almost never degrade into needs put situation.
> Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
> ---
> security/apparmor/include/cred.h | 21 ++++++---
> security/apparmor/lsm.c | 75 ++++++++++++++++++++------------
> security/apparmor/policy.c | 12 ++---
> 3 files changed, 67 insertions(+), 41 deletions(-)
>
> diff --git a/security/apparmor/include/cred.h b/security/apparmor/include/cred.h
> index 7265d2f81dd5..fc5791937694 100644
> --- a/security/apparmor/include/cred.h
> +++ b/security/apparmor/include/cred.h
> @@ -114,7 +114,12 @@ static inline struct aa_label *aa_get_current_label(void)
> return aa_get_label(l);
> }
>
> -#define __end_current_label_crit_section(X) end_current_label_crit_section(X)
> +static inline void __end_current_label_crit_section(struct aa_label *label,
> + bool needput)
> +{
> + if (unlikely(needput))
> + aa_put_label(label);
> +}
>
> /**
> * end_label_crit_section - put a reference found with begin_current_label..
> @@ -142,13 +147,16 @@ static inline void end_current_label_crit_section(struct aa_label *label)
> * critical section between __begin_current_label_crit_section() ..
> * __end_current_label_crit_section()
> */
> -static inline struct aa_label *__begin_current_label_crit_section(void)
> +static inline struct aa_label *__begin_current_label_crit_section(bool *needput)
> {
> struct aa_label *label = aa_current_raw_label();
>
> - if (label_is_stale(label))
> - label = aa_get_newest_label(label);
> + if (label_is_stale(label)) {
> + *needput = true;
> + return aa_get_newest_label(label);
> + }
>
> + *needput = false;
> return label;
> }
>
> @@ -184,10 +192,11 @@ static inline struct aa_ns *aa_get_current_ns(void)
> {
> struct aa_label *label;
> struct aa_ns *ns;
> + bool needput;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> ns = aa_get_ns(labels_ns(label));
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return ns;
> }
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index 7952e8cab353..c2be3c6f9d3e 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -127,14 +127,15 @@ static int apparmor_ptrace_access_check(struct task_struct *child,
> struct aa_label *tracer, *tracee;
> const struct cred *cred;
> int error;
> + bool needput;
>
> cred = get_task_cred(child);
> tracee = cred_label(cred); /* ref count on cred */
> - tracer = __begin_current_label_crit_section();
> + tracer = __begin_current_label_crit_section(&needput);
> error = aa_may_ptrace(current_cred(), tracer, cred, tracee,
> (mode & PTRACE_MODE_READ) ? AA_PTRACE_READ
> : AA_PTRACE_TRACE);
> - __end_current_label_crit_section(tracer);
> + __end_current_label_crit_section(tracer, needput);
> put_cred(cred);
>
> return error;
> @@ -145,14 +146,15 @@ static int apparmor_ptrace_traceme(struct task_struct *parent)
> struct aa_label *tracer, *tracee;
> const struct cred *cred;
> int error;
> + bool needput;
>
> - tracee = __begin_current_label_crit_section();
> + tracee = __begin_current_label_crit_section(&needput);
> cred = get_task_cred(parent);
> tracer = cred_label(cred); /* ref count on cred */
> error = aa_may_ptrace(cred, tracer, current_cred(), tracee,
> AA_PTRACE_TRACE);
> put_cred(cred);
> - __end_current_label_crit_section(tracee);
> + __end_current_label_crit_section(tracee, needput);
>
> return error;
> }
> @@ -221,12 +223,13 @@ static int common_perm(const char *op, const struct path *path, u32 mask,
> {
> struct aa_label *label;
> int error = 0;
> + bool needput;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> if (!unconfined(label))
> error = aa_path_perm(op, current_cred(), label, path, 0, mask,
> cond);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -524,14 +527,15 @@ static int common_file_perm(const char *op, struct file *file, u32 mask,
> {
> struct aa_label *label;
> int error = 0;
> + bool needput;
>
> /* don't reaudit files closed during inheritance */
> - if (file->f_path.dentry == aa_null.dentry)
> + if (unlikely(file->f_path.dentry == aa_null.dentry))
> return -EACCES;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> error = aa_file_perm(op, current_cred(), label, file, mask, in_atomic);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -664,15 +668,16 @@ static int apparmor_uring_override_creds(const struct cred *new)
> struct aa_profile *profile;
> struct aa_label *label;
> int error;
> + bool needput;
> DEFINE_AUDIT_DATA(ad, LSM_AUDIT_DATA_NONE, AA_CLASS_IO_URING,
> OP_URING_OVERRIDE);
>
> ad.uring.target = cred_label(new);
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> error = fn_for_each(label, profile,
> profile_uring(profile, AA_MAY_OVERRIDE_CRED,
> cred_label(new), CAP_SYS_ADMIN, &ad));
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -688,14 +693,15 @@ static int apparmor_uring_sqpoll(void)
> struct aa_profile *profile;
> struct aa_label *label;
> int error;
> + bool needput;
> DEFINE_AUDIT_DATA(ad, LSM_AUDIT_DATA_NONE, AA_CLASS_IO_URING,
> OP_URING_SQPOLL);
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> error = fn_for_each(label, profile,
> profile_uring(profile, AA_MAY_CREATE_SQPOLL,
> NULL, CAP_SYS_ADMIN, &ad));
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -706,6 +712,7 @@ static int apparmor_sb_mount(const char *dev_name, const struct path *path,
> {
> struct aa_label *label;
> int error = 0;
> + bool needput;
>
> /* Discard magic */
> if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
> @@ -713,7 +720,7 @@ static int apparmor_sb_mount(const char *dev_name, const struct path *path,
>
> flags &= ~AA_MS_IGNORE_MASK;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> if (!unconfined(label)) {
> if (flags & MS_REMOUNT)
> error = aa_remount(current_cred(), label, path, flags,
> @@ -732,7 +739,7 @@ static int apparmor_sb_mount(const char *dev_name, const struct path *path,
> error = aa_new_mount(current_cred(), label, dev_name,
> path, type, flags, data);
> }
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -742,12 +749,13 @@ static int apparmor_move_mount(const struct path *from_path,
> {
> struct aa_label *label;
> int error = 0;
> + bool needput;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> if (!unconfined(label))
> error = aa_move_mount(current_cred(), label, from_path,
> to_path);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -756,11 +764,12 @@ static int apparmor_sb_umount(struct vfsmount *mnt, int flags)
> {
> struct aa_label *label;
> int error = 0;
> + bool needput;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> if (!unconfined(label))
> error = aa_umount(current_cred(), label, mnt, flags);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -984,10 +993,12 @@ static void apparmor_bprm_committed_creds(const struct linux_binprm *bprm)
>
> static void apparmor_current_getlsmprop_subj(struct lsm_prop *prop)
> {
> - struct aa_label *label = __begin_current_label_crit_section();
> + struct aa_label *label;
> + bool needput;
>
> + label = __begin_current_label_crit_section(&needput);
> prop->apparmor.label = label;
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
> }
>
> static void apparmor_task_getlsmprop_obj(struct task_struct *p,
> @@ -1002,13 +1013,16 @@ static void apparmor_task_getlsmprop_obj(struct task_struct *p,
> static int apparmor_task_setrlimit(struct task_struct *task,
> unsigned int resource, struct rlimit *new_rlim)
> {
> - struct aa_label *label = __begin_current_label_crit_section();
> + struct aa_label *label;
> int error = 0;
> + bool needput;
> +
> + label = __begin_current_label_crit_section(&needput);
>
> if (!unconfined(label))
> error = aa_task_setrlimit(current_cred(), label, task,
> resource, new_rlim);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> @@ -1019,6 +1033,7 @@ static int apparmor_task_kill(struct task_struct *target, struct kernel_siginfo
> const struct cred *tc;
> struct aa_label *cl, *tl;
> int error;
> + bool needput;
>
> tc = get_task_cred(target);
> tl = aa_get_newest_cred_label(tc);
> @@ -1030,9 +1045,9 @@ static int apparmor_task_kill(struct task_struct *target, struct kernel_siginfo
> error = aa_may_signal(cred, cl, tc, tl, sig);
> aa_put_label(cl);
> } else {
> - cl = __begin_current_label_crit_section();
> + cl = __begin_current_label_crit_section(&needput);
> error = aa_may_signal(current_cred(), cl, tc, tl, sig);
> - __end_current_label_crit_section(cl);
> + __end_current_label_crit_section(cl, needput);
> }
> aa_put_label(tl);
> put_cred(tc);
> @@ -1133,10 +1148,11 @@ static int apparmor_unix_stream_connect(struct sock *sk, struct sock *peer_sk,
> struct aa_sk_ctx *new_ctx = aa_sock(newsk);
> struct aa_label *label;
> int error;
> + bool needput;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> error = unix_connect_perm(current_cred(), label, sk, peer_sk);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> if (error)
> return error;
> @@ -1163,8 +1179,9 @@ static int apparmor_unix_may_send(struct socket *sock, struct socket *peer)
> struct aa_sk_ctx *peer_ctx = aa_sock(peer->sk);
> struct aa_label *label;
> int error;
> + bool needput;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> error = xcheck(aa_unix_peer_perm(current_cred(),
> label, OP_SENDMSG, AA_MAY_SEND,
> sock->sk, peer->sk, NULL),
> @@ -1172,7 +1189,7 @@ static int apparmor_unix_may_send(struct socket *sock, struct socket *peer)
> peer_ctx->label, OP_SENDMSG,
> AA_MAY_RECEIVE,
> peer->sk, sock->sk, label));
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return error;
> }
> diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c
> index 1f532fe48a1c..a60bb7d9b583 100644
> --- a/security/apparmor/policy.c
> +++ b/security/apparmor/policy.c
> @@ -870,11 +870,11 @@ bool aa_policy_admin_capable(const struct cred *subj_cred,
> bool aa_current_policy_view_capable(struct aa_ns *ns)
> {
> struct aa_label *label;
> - bool res;
> + bool needput, res;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> res = aa_policy_view_capable(current_cred(), label, ns);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return res;
> }
> @@ -882,11 +882,11 @@ bool aa_current_policy_view_capable(struct aa_ns *ns)
> bool aa_current_policy_admin_capable(struct aa_ns *ns)
> {
> struct aa_label *label;
> - bool res;
> + bool needput, res;
>
> - label = __begin_current_label_crit_section();
> + label = __begin_current_label_crit_section(&needput);
> res = aa_policy_admin_capable(current_cred(), label, ns);
> - __end_current_label_crit_section(label);
> + __end_current_label_crit_section(label, needput);
>
> return res;
> }
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