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author | Eric W. Biederman <ebiederm@xmission.com> | 2016-10-14 02:23:16 (GMT) |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-01-06 09:40:13 (GMT) |
commit | 694a95fa6dae4991f16cda333d897ea063021fed (patch) | |
tree | ac12876552e1b6585013a0e2932cf5da3c91def6 /mm/init-mm.c | |
parent | cfa2d65b2622d14b2f1368fbc9a6b4ab85141644 (diff) | |
download | linux-694a95fa6dae4991f16cda333d897ea063021fed.tar.xz |
mm: Add a user_ns owner to mm_struct and fix ptrace permission checks
commit bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 upstream.
During exec dumpable is cleared if the file that is being executed is
not readable by the user executing the file. A bug in
ptrace_may_access allows reading the file if the executable happens to
enter into a subordinate user namespace (aka clone(CLONE_NEWUSER),
unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER).
This problem is fixed with only necessary userspace breakage by adding
a user namespace owner to mm_struct, captured at the time of exec, so
it is clear in which user namespace CAP_SYS_PTRACE must be present in
to be able to safely give read permission to the executable.
The function ptrace_may_access is modified to verify that the ptracer
has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns.
This ensures that if the task changes it's cred into a subordinate
user namespace it does not become ptraceable.
The function ptrace_attach is modified to only set PT_PTRACE_CAP when
CAP_SYS_PTRACE is held over task->mm->user_ns. The intent of
PT_PTRACE_CAP is to be a flag to note that whatever permission changes
the task might go through the tracer has sufficient permissions for
it not to be an issue. task->cred->user_ns is always the same
as or descendent of mm->user_ns. Which guarantees that having
CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks
credentials.
To prevent regressions mm->dumpable and mm->user_ns are not considered
when a task has no mm. As simply failing ptrace_may_attach causes
regressions in privileged applications attempting to read things
such as /proc/<pid>/stat
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Cyrill Gorcunov <gorcunov@openvz.org>
Fixes: 8409cca70561 ("userns: allow ptrace from non-init user namespaces")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm/init-mm.c')
-rw-r--r-- | mm/init-mm.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/init-mm.c b/mm/init-mm.c index a56a851..975e49f 100644 --- a/mm/init-mm.c +++ b/mm/init-mm.c @@ -6,6 +6,7 @@ #include <linux/cpumask.h> #include <linux/atomic.h> +#include <linux/user_namespace.h> #include <asm/pgtable.h> #include <asm/mmu.h> @@ -21,5 +22,6 @@ struct mm_struct init_mm = { .mmap_sem = __RWSEM_INITIALIZER(init_mm.mmap_sem), .page_table_lock = __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock), .mmlist = LIST_HEAD_INIT(init_mm.mmlist), + .user_ns = &init_user_ns, INIT_MM_CONTEXT(init_mm) }; |