Messages in this thread | ![/](/images/icornerl.gif) | | From | Giuseppe Scrivano <> | Subject | Re: [PATCH v2 1/2] exec: add PR_HIDE_SELF_EXE prctl | Date | Thu, 19 Jan 2023 19:02:00 +0100 |
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Brian Masney <bmasney@redhat.com> writes:
> On Thu, Jan 19, 2023 at 06:07:17PM +0100, Giuseppe Scrivano wrote: >> This patch adds a new prctl called PR_HIDE_SELF_EXE which allows >> processes to hide their own /proc/*/exe file. When this prctl is >> used, every access to /proc/*/exe for the calling process will >> fail with ENOENT. >> >> This is useful for preventing issues like CVE-2019-5736, where an >> attacker can gain host root access by overwriting the binary >> in OCI runtimes through file-descriptor mishandling in containers. >> >> The current fix for CVE-2019-5736 is to create a read-only copy or >> a bind-mount of the current executable, and then re-exec the current >> process. With the new prctl, the read-only copy or bind-mount copy is >> not needed anymore. >> >> While map_files/ also might contain symlinks to files in host, >> proc_map_files_get_link() permissions checks are already sufficient. >> >> Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com> >> --- >> fs/exec.c | 1 + >> fs/proc/base.c | 8 +++++--- >> include/linux/sched.h | 5 +++++ >> include/uapi/linux/prctl.h | 3 +++ >> kernel/sys.c | 9 +++++++++ >> tools/include/uapi/linux/prctl.h | 3 +++ >> 6 files changed, 26 insertions(+), 3 deletions(-) >> >> v1: https://lkml.org/lkml/2023/1/4/334 >> >> Differences from v1: >> >> - amended more information in the commit message wrt map_files not >> requiring the same protection. >> - changed the test to verify PR_HIDE_SELF_EXE cannot be unset after >> a fork. >> >> diff --git a/fs/exec.c b/fs/exec.c >> index ab913243a367..5a5dd964c3a3 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -1855,6 +1855,7 @@ static int bprm_execve(struct linux_binprm *bprm, >> /* execve succeeded */ >> current->fs->in_exec = 0; >> current->in_execve = 0; >> + task_clear_hide_self_exe(current); > > [snip] > >> rseq_execve(current); >> acct_update_integrals(current); >> task_numa_free(current, false); >> diff --git a/fs/proc/base.c b/fs/proc/base.c >> index 9e479d7d202b..959968e2da0d 100644 >> --- a/fs/proc/base.c >> +++ b/fs/proc/base.c >> @@ -1723,19 +1723,21 @@ static int proc_exe_link(struct dentry *dentry, struct path *exe_path) >> { >> struct task_struct *task; >> struct file *exe_file; >> + long hide_self_exe; >> >> task = get_proc_task(d_inode(dentry)); >> if (!task) >> return -ENOENT; >> exe_file = get_task_exe_file(task); >> + hide_self_exe = task_hide_self_exe(task); > > Perhaps I am missing something, but where is task_clear_hide_self_exe() > and task_hide_self_exe() defined?
they are defined with:
TASK_PFA_TEST(HIDE_SELF_EXE, hide_self_exe) TASK_PFA_SET(HIDE_SELF_EXE, hide_self_exe) TASK_PFA_CLEAR(HIDE_SELF_EXE, hide_self_exe)
Regards, Giuseppe
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