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authorMike Rapoport <rppt@linux.ibm.com>2019-11-30 17:58:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-12-01 12:59:10 -0800
commit3c1c24d91ffd536de0a64688a9df7f49e58fadbc (patch)
tree69fdc01c320cfd21b656fb76616c663c33bef80f /fs/userfaultfd.c
parent9d4678eb170c4c632174d1fec8ecee31c2f314f9 (diff)
downloadlinux-3c1c24d91ffd536de0a64688a9df7f49e58fadbc.tar.bz2
userfaultfd: require CAP_SYS_PTRACE for UFFD_FEATURE_EVENT_FORK
A while ago Andy noticed (http://lkml.kernel.org/r/CALCETrWY+5ynDct7eU_nDUqx=okQvjm=Y5wJvA4ahBja=CQXGw@mail.gmail.com) 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>
Diffstat (limited to 'fs/userfaultfd.c')
-rw-r--r--fs/userfaultfd.c18
1 files changed, 11 insertions, 7 deletions
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index d90c4c5aa3cc..90acd2812ea7 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1835,13 +1835,12 @@ 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;
@@ -1854,6 +1853,11 @@ 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,