Messages in this thread Patch in this message | | | From | Giuseppe Scrivano <> | Subject | [PATCH RFC 1/2] exec: add PR_HIDE_SELF_EXE prctl | Date | Wed, 21 Dec 2022 11:19:12 +0100 |
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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.
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(-)
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); 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); put_task_struct(task); - if (exe_file) { + if (exe_file && !hide_self_exe) { *exe_path = exe_file->f_path; path_get(&exe_file->f_path); fput(exe_file); return 0; - } else - return -ENOENT; + } + return -ENOENT; } static const char *proc_pid_get_link(struct dentry *dentry, diff --git a/include/linux/sched.h b/include/linux/sched.h index 853d08f7562b..8db32d5fc285 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1790,6 +1790,7 @@ static __always_inline bool is_percpu_thread(void) #define PFA_SPEC_IB_DISABLE 5 /* Indirect branch speculation restricted */ #define PFA_SPEC_IB_FORCE_DISABLE 6 /* Indirect branch speculation permanently restricted */ #define PFA_SPEC_SSB_NOEXEC 7 /* Speculative Store Bypass clear on execve() */ +#define PFA_HIDE_SELF_EXE 8 /* Hide /proc/self/exe for the process */ #define TASK_PFA_TEST(name, func) \ static inline bool task_##func(struct task_struct *p) \ @@ -1832,6 +1833,10 @@ TASK_PFA_CLEAR(SPEC_IB_DISABLE, spec_ib_disable) TASK_PFA_TEST(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable) TASK_PFA_SET(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable) +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) + static inline void current_restore_flags(unsigned long orig_flags, unsigned long flags) { diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index a5e06dcbba13..f12f3df12468 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -284,4 +284,7 @@ struct prctl_mm_map { #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 +#define PR_SET_HIDE_SELF_EXE 65 +#define PR_GET_HIDE_SELF_EXE 66 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index 5fd54bf0e886..e992f1b72973 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2626,6 +2626,15 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_SET_VMA: error = prctl_set_vma(arg2, arg3, arg4, arg5); break; + case PR_SET_HIDE_SELF_EXE: + if (arg2 != 1 || arg3 || arg4 || arg5) + return -EINVAL; + task_set_hide_self_exe(current); + break; + case PR_GET_HIDE_SELF_EXE: + if (arg2 || arg3 || arg4 || arg5) + return -EINVAL; + return task_hide_self_exe(current) ? 1 : 0; default: error = -EINVAL; break; diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h index a5e06dcbba13..f12f3df12468 100644 --- a/tools/include/uapi/linux/prctl.h +++ b/tools/include/uapi/linux/prctl.h @@ -284,4 +284,7 @@ struct prctl_mm_map { #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 +#define PR_SET_HIDE_SELF_EXE 65 +#define PR_GET_HIDE_SELF_EXE 66 + #endif /* _LINUX_PRCTL_H */ -- 2.38.1
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