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authorEric W. Biederman <ebiederm@xmission.com>2022-02-09 16:22:20 -0600
committerEric W. Biederman <ebiederm@xmission.com>2022-02-17 09:11:02 -0600
commita55d07294f1e9b576093bdfa95422f8119941e83 (patch)
treec570ddac28cfb2800c105baafe568394ce184ceb
parent8f2f9c4d82f24f172ae439e5035fc1e0e4c229dd (diff)
downloadlwn-a55d07294f1e9b576093bdfa95422f8119941e83.tar.gz
lwn-a55d07294f1e9b576093bdfa95422f8119941e83.zip
ucounts: Base set_cred_ucounts changes on the real user
Michal Koutný <mkoutny@suse.com> wrote: > Tasks are associated to multiple users at once. Historically and as per > setrlimit(2) RLIMIT_NPROC is enforce based on real user ID. > > The commit 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts") > made the accounting structure "indexed" by euid and hence potentially > account tasks differently. > > The effective user ID may be different e.g. for setuid programs but > those are exec'd into already existing task (i.e. below limit), so > different accounting is moot. > > Some special setresuid(2) users may notice the difference, justifying > this fix. I looked at cred->ucount and it is only used for rlimit operations that were previously stored in cred->user. Making the fact cred->ucount can refer to a different user from cred->user a bug, affecting all uses of cred->ulimit not just RLIMIT_NPROC. Fix set_cred_ucounts to always use the real uid not the effective uid. Further simplify set_cred_ucounts by noticing that set_cred_ucounts somehow retained a draft version of the check to see if alloc_ucounts was needed that checks the new->user and new->user_ns against the current_real_cred(). Remove that draft version of the check. All that matters for setting the cred->ucounts are the user_ns and uid fields in the cred. Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20220207121800.5079-4-mkoutny@suse.com Link: https://lkml.kernel.org/r/20220216155832.680775-3-ebiederm@xmission.com Reported-by: Michal Koutný <mkoutny@suse.com> Reviewed-by: Michal Koutný <mkoutny@suse.com> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts") Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-rw-r--r--kernel/cred.c9
1 files changed, 2 insertions, 7 deletions
diff --git a/kernel/cred.c b/kernel/cred.c
index 473d17c431f3..933155c96922 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -665,21 +665,16 @@ EXPORT_SYMBOL(cred_fscmp);
int set_cred_ucounts(struct cred *new)
{
- struct task_struct *task = current;
- const struct cred *old = task->real_cred;
struct ucounts *new_ucounts, *old_ucounts = new->ucounts;
- if (new->user == old->user && new->user_ns == old->user_ns)
- return 0;
-
/*
* This optimization is needed because alloc_ucounts() uses locks
* for table lookups.
*/
- if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
+ if (old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->uid))
return 0;
- if (!(new_ucounts = alloc_ucounts(new->user_ns, new->euid)))
+ if (!(new_ucounts = alloc_ucounts(new->user_ns, new->uid)))
return -EAGAIN;
new->ucounts = new_ucounts;