Merge branch 'ucount-rlimit-fixes-for-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull ucounts fixes from Eric Biederman:
 "Michal Koutný recently found some bugs in the enforcement of
  RLIMIT_NPROC in the recent ucount rlimit implementation.

  In this set of patches I have developed a very conservative approach
  changing only what is necessary to fix the bugs that I can see
  clearly. Cleanups and anything that is making the code more consistent
  can follow after we have the code working as it has historically.

  The problem is not so much inconsistencies (although those exist) but
  that it is very difficult to figure out what the code should be doing
  in the case of RLIMIT_NPROC.

  All other rlimits are only enforced where the resource is acquired
  (allocated). RLIMIT_NPROC by necessity needs to be enforced in an
  additional location, and our current implementation stumbled it's way
  into that implementation"

* 'ucount-rlimit-fixes-for-v5.17' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  ucounts: Handle wrapping in is_ucounts_overlimit
  ucounts: Move RLIMIT_NPROC handling after set_user
  ucounts: Base set_cred_ucounts changes on the real user
  ucounts: Enforce RLIMIT_NPROC not RLIMIT_NPROC+1
  rlimit: Fix RLIMIT_NPROC enforcement failure caused by capability calls in set_user

1 files changed, 14 insertions, 6 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index ecc4cf019242..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
@@ -480,15 +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 &&
-			!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
+			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;
 }
 
 /*
@@ -563,6 +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:
@@ -625,6 +631,7 @@ long __sys_setuid(uid_t uid)
 	if (retval < 0)
 		goto error;
 
+	flag_nproc_exceeded(new);
 	return commit_creds(new);
 
 error:
@@ -704,6 +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: