Add a reference to ucounts for each cred
authorAlexey Gladkov <legion@kernel.org>
Thu, 22 Apr 2021 12:27:09 +0000 (14:27 +0200)
committerEric W. Biederman <ebiederm@xmission.com>
Fri, 30 Apr 2021 19:14:00 +0000 (14:14 -0500)
commit905ae01c4ae2ae3df05bb141801b1db4b7d83c61
treec4216c817bd6859c8028a25900bcfe4330c1e3c9
parentf9c82a4ea89c384d49ce03768ba88d049ed3f1f0
Add a reference to ucounts for each cred

For RLIMIT_NPROC and some other rlimits the user_struct that holds the
global limit is kept alive for the lifetime of a process by keeping it
in struct cred. Adding a pointer to ucounts in the struct cred will
allow to track RLIMIT_NPROC not only for user in the system, but for
user in the user_namespace.

Updating ucounts may require memory allocation which may fail. So, we
cannot change cred.ucounts in the commit_creds() because this function
cannot fail and it should always return 0. For this reason, we modify
cred.ucounts before calling the commit_creds().

Changelog

v6:
* Fix null-ptr-deref in is_ucounts_overlimit() detected by trinity. This
  error was caused by the fact that cred_alloc_blank() left the ucounts
  pointer empty.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/b37aaef28d8b9b0d757e07ba6dd27281bbe39259.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
fs/exec.c
include/linux/cred.h
include/linux/user_namespace.h
kernel/cred.c
kernel/fork.c
kernel/sys.c
kernel/ucount.c
kernel/user_namespace.c