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@xxxxxxxxxxxxxxx # v4.7+
Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx>
---
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
