linux-kernel - [PATCH v2 4/5] ucounts: Move RLIMIT_NPROC handling after set

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Date:   Wed, 16 Feb 2022 09:58:31 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     Alexey Gladkov <legion@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Solar Designer <solar@...nwall.com>,
        Ran Xiaokai <ran.xiaokai@....com.cn>,
        containers@...ts.linux-foundation.org,
        Michal Koutný <mkoutny@...e.com>,
        linux-api@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>, stable@...r.kernel.org
Subject: [PATCH v2 4/5] ucounts: Move RLIMIT_NPROC handling after set_user

During set*id() which cred->ucounts to charge the the current process
to is not known until after set_cred_ucounts.  So move the
RLIMIT_NPROC checking into a new helper flag_nproc_exceeded and call
flag_nproc_exceeded after set_cred_ucounts.

This is very much an arbitrary subset of the places where we currently
change the RLIMIT_NPROC accounting, designed to preserve the existing
logic.

Fixing the existing logic will be the subject of another series of
changes.

Cc: stable@...r.kernel.org
Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/sys.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 8dd938a3d2bf..97dc9e5d6bf9 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -472,6 +472,16 @@ static int set_user(struct cred *new)
 	if (!new_user)
 		return -EAGAIN;
 
+	free_uid(new->user);
+	new->user = new_user;
+	return 0;
+}
+
+static void flag_nproc_exceeded(struct cred *new)
+{
+	if (new->ucounts == current_ucounts())
+		return;
+
 	/*
 	 * We don't fail in case of NPROC limit excess here because too many
 	 * poorly written programs don't check set*uid() return code, assuming
@@ -480,14 +490,10 @@ static int set_user(struct cred *new)
 	 * failure to the execve() stage.
 	 */
 	if (is_ucounts_overlimit(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) &&
-			new_user != INIT_USER)
+			new->user != INIT_USER)
 		current->flags |= PF_NPROC_EXCEEDED;
 	else
 		current->flags &= ~PF_NPROC_EXCEEDED;
-
-	free_uid(new->user);
-	new->user = new_user;
-	return 0;
 }
 
 /*
@@ -562,6 +568,7 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
 	if (retval < 0)
 		goto error;
 
+	flag_nproc_exceeded(new);
 	return commit_creds(new);
 
 error:
@@ -624,6 +631,7 @@ long __sys_setuid(uid_t uid)
 	if (retval < 0)
 		goto error;
 
+	flag_nproc_exceeded(new);
 	return commit_creds(new);
 
 error:
@@ -703,6 +711,7 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
 	if (retval < 0)
 		goto error;
 
+	flag_nproc_exceeded(new);
 	return commit_creds(new);
 
 error:
-- 
2.29.2