Re: [PATCH] procfs: block chmod on /proc/thread-self/comm

+Cc Thomas Weißschuh thomas@t-8ch.de as this seems quite related to his finding about /proc/self/net:

https://lore.kernel.org/lkml/20230624-proc-net-setattr-v1-0-73176812adee@wei...

On Thu, Jul 13, 2023 at 10:19:04PM +1000, Aleksa Sarai wrote:

Due to an oversight in commit 1b3044e39a89 ("procfs: fix pthread cross-thread naming if !PR_DUMPABLE") in switching from REG to NOD, chmod operations on /proc/thread-self/comm were no longer blocked as they are on almost all other procfs files.

A very similar situation with /proc/self/environ was used to as a root exploit a long time ago, but procfs has SB_I_NOEXEC so this is simply a correctness issue.

Ref: https://lwn.net/Articles/191954/ Ref: 6d76fa58b050 ("Don't allow chmod() on the /proc/<pid>/ files") Fixes: 1b3044e39a89 ("procfs: fix pthread cross-thread naming if !PR_DUMPABLE") Cc: stable@vger.kernel.org # v4.7+ Signed-off-by: Aleksa Sarai cyphar@cyphar.com

---

fs/proc/base.c | 3 ++- tools/testing/selftests/nolibc/nolibc-test.c | 4 ++++ 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c index 05452c3b9872..7394229816f3 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -3583,7 +3583,8 @@ static int proc_tid_comm_permission(struct mnt_idmap *idmap, } static const struct inode_operations proc_tid_comm_inode_operations = {

• .permission = proc_tid_comm_permission,
  

• .setattr	= proc_setattr,
  

• .permission	= proc_tid_comm_permission,
  

}; /* diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c index 486334981e60..08f0969208eb 100644 --- a/tools/testing/selftests/nolibc/nolibc-test.c +++ b/tools/testing/selftests/nolibc/nolibc-test.c @@ -580,6 +580,10 @@ int run_syscall(int min, int max) CASE_TEST(chmod_net); EXPECT_SYSZR(proc, chmod("/proc/self/net", 0555)); break; CASE_TEST(chmod_self); EXPECT_SYSER(proc, chmod("/proc/self", 0555), -1, EPERM); break; CASE_TEST(chown_self); EXPECT_SYSER(proc, chown("/proc/self", 0, 0), -1, EPERM); break;

• CASE_TEST(chmod_self_comm);   EXPECT_SYSER(proc, chmod("/proc/self/comm", 0777), -1, EPERM); break;
  

• CASE_TEST(chmod_tid_comm);    EXPECT_SYSER(proc, chmod("/proc/thread-self/comm", 0777), -1, EPERM); break;
  

• CASE_TEST(chmod_self_environ);EXPECT_SYSER(proc, chmod("/proc/self/environ", 0777), -1, EPERM); break;
  

• CASE_TEST(chmod_tid_environ); EXPECT_SYSER(proc, chmod("/proc/thread-self/environ", 0777), -1, EPERM); break;
  

  CASE_TEST(chroot_root); EXPECT_SYSZR(euid0, chroot("/")); break; CASE_TEST(chroot_blah); EXPECT_SYSER(1, chroot("/proc/self/blah"), -1, ENOENT); break; CASE_TEST(chroot_exe); EXPECT_SYSER(proc, chroot("/proc/self/exe"), -1, ENOTDIR); break;

-- 2.41.0