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authorEric W. Biederman <ebiederm@xmission.com>2016-11-22 21:06:50 +0300
committerEric W. Biederman <ebiederm@xmission.com>2016-11-22 21:57:38 +0300
commit84d77d3f06e7e8dea057d10e8ec77ad71f721be3 (patch)
tree6efbcfc0877019c2afbdf11596362c8198ebdd0d /kernel/ptrace.c
parent64b875f7ac8a5d60a4e191479299e931ee949b67 (diff)
downloadlinux-84d77d3f06e7e8dea057d10e8ec77ad71f721be3.tar.xz
ptrace: Don't allow accessing an undumpable mm
It is the reasonable expectation that if an executable file is not readable there will be no way for a user without special privileges to read the file. This is enforced in ptrace_attach but if ptrace is already attached before exec there is no enforcement for read-only executables. As the only way to read such an mm is through access_process_vm spin a variant called ptrace_access_vm that will fail if the target process is not being ptraced by the current process, or the current process did not have sufficient privileges when ptracing began to read the target processes mm. In the ptrace implementations replace access_process_vm by ptrace_access_vm. There remain several ptrace sites that still use access_process_vm as they are reading the target executables instructions (for kernel consumption) or register stacks. As such it does not appear necessary to add a permission check to those calls. This bug has always existed in Linux. Fixes: v1.0 Cc: stable@vger.kernel.org Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel/ptrace.c')
-rw-r--r--kernel/ptrace.c42
1 files changed, 36 insertions, 6 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index e82c15cadd6d..49ba7c1ade9d 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -27,6 +27,35 @@
#include <linux/cn_proc.h>
#include <linux/compat.h>
+/*
+ * Access another process' address space via ptrace.
+ * Source/target buffer must be kernel space,
+ * Do not walk the page table directly, use get_user_pages
+ */
+int ptrace_access_vm(struct task_struct *tsk, unsigned long addr,
+ void *buf, int len, unsigned int gup_flags)
+{
+ struct mm_struct *mm;
+ int ret;
+
+ mm = get_task_mm(tsk);
+ if (!mm)
+ return 0;
+
+ if (!tsk->ptrace ||
+ (current != tsk->parent) ||
+ ((get_dumpable(mm) != SUID_DUMP_USER) &&
+ !ptracer_capable(tsk, mm->user_ns))) {
+ mmput(mm);
+ return 0;
+ }
+
+ ret = __access_remote_vm(tsk, mm, addr, buf, len, gup_flags);
+ mmput(mm);
+
+ return ret;
+}
+
/*
* ptrace a task: make the debugger its new parent and
@@ -535,7 +564,8 @@ int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst
int this_len, retval;
this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
- retval = access_process_vm(tsk, src, buf, this_len, FOLL_FORCE);
+ retval = ptrace_access_vm(tsk, src, buf, this_len, FOLL_FORCE);
+
if (!retval) {
if (copied)
break;
@@ -562,7 +592,7 @@ int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long ds
this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
if (copy_from_user(buf, src, this_len))
return -EFAULT;
- retval = access_process_vm(tsk, dst, buf, this_len,
+ retval = ptrace_access_vm(tsk, dst, buf, this_len,
FOLL_FORCE | FOLL_WRITE);
if (!retval) {
if (copied)
@@ -1126,7 +1156,7 @@ int generic_ptrace_peekdata(struct task_struct *tsk, unsigned long addr,
unsigned long tmp;
int copied;
- copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), FOLL_FORCE);
+ copied = ptrace_access_vm(tsk, addr, &tmp, sizeof(tmp), FOLL_FORCE);
if (copied != sizeof(tmp))
return -EIO;
return put_user(tmp, (unsigned long __user *)data);
@@ -1137,7 +1167,7 @@ int generic_ptrace_pokedata(struct task_struct *tsk, unsigned long addr,
{
int copied;
- copied = access_process_vm(tsk, addr, &data, sizeof(data),
+ copied = ptrace_access_vm(tsk, addr, &data, sizeof(data),
FOLL_FORCE | FOLL_WRITE);
return (copied == sizeof(data)) ? 0 : -EIO;
}
@@ -1155,7 +1185,7 @@ int compat_ptrace_request(struct task_struct *child, compat_long_t request,
switch (request) {
case PTRACE_PEEKTEXT:
case PTRACE_PEEKDATA:
- ret = access_process_vm(child, addr, &word, sizeof(word),
+ ret = ptrace_access_vm(child, addr, &word, sizeof(word),
FOLL_FORCE);
if (ret != sizeof(word))
ret = -EIO;
@@ -1165,7 +1195,7 @@ int compat_ptrace_request(struct task_struct *child, compat_long_t request,
case PTRACE_POKETEXT:
case PTRACE_POKEDATA:
- ret = access_process_vm(child, addr, &data, sizeof(data),
+ ret = ptrace_access_vm(child, addr, &data, sizeof(data),
FOLL_FORCE | FOLL_WRITE);
ret = (ret != sizeof(data) ? -EIO : 0);
break;