From: Mike Rapoport rppt@linux.ibm.com
[ Upstream commit 3c1c24d91ffd536de0a64688a9df7f49e58fadbc ]
A while ago Andy noticed (http://lkml.kernel.org/r/CALCETrWY+5ynDct7eU_nDUqx=okQvjm=Y5wJvA4ahBja=CQXGw...) that UFFD_FEATURE_EVENT_FORK used by an unprivileged user may have security implications.
As the first step of the solution the following patch limits the availably of UFFD_FEATURE_EVENT_FORK only for those having CAP_SYS_PTRACE.
The usage of CAP_SYS_PTRACE ensures compatibility with CRIU.
Yet, if there are other users of non-cooperative userfaultfd that run without CAP_SYS_PTRACE, they would be broken :(
Current implementation of UFFD_FEATURE_EVENT_FORK modifies the file descriptor table from the read() implementation of uffd, which may have security implications for unprivileged use of the userfaultfd.
Limit availability of UFFD_FEATURE_EVENT_FORK only for callers that have CAP_SYS_PTRACE.
Link: http://lkml.kernel.org/r/1572967777-8812-2-git-send-email-rppt@linux.ibm.com Signed-off-by: Mike Rapoport rppt@linux.ibm.com Reviewed-by: Andrea Arcangeli aarcange@redhat.com Cc: Daniel Colascione dancol@google.com Cc: Jann Horn jannh@google.com Cc: Lokesh Gidra lokeshgidra@google.com Cc: Nick Kralevich nnk@google.com Cc: Nosh Minwalla nosh@google.com Cc: Pavel Emelyanov ovzxemul@gmail.com Cc: Tim Murray timmurray@google.com Cc: Aleksa Sarai cyphar@cyphar.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/userfaultfd.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index f9fd18670e22..d99d166fd892 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1834,13 +1834,12 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx, if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) goto out; features = uffdio_api.features; - if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) { - memset(&uffdio_api, 0, sizeof(uffdio_api)); - if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) - goto out; - ret = -EINVAL; - goto out; - } + ret = -EINVAL; + if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) + goto err_out; + ret = -EPERM; + if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE)) + goto err_out; /* report all available features and ioctls to userland */ uffdio_api.features = UFFD_API_FEATURES; uffdio_api.ioctls = UFFD_API_IOCTLS; @@ -1853,6 +1852,11 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx, ret = 0; out: return ret; +err_out: + memset(&uffdio_api, 0, sizeof(uffdio_api)); + if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) + ret = -EFAULT; + goto out; }
static long userfaultfd_ioctl(struct file *file, unsigned cmd,