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userfaultfd: require CAP_SYS_PTRACE for UFFD_FEATURE_EVENT_FORK
[ Upstream commit 3c1c24d91f
]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
parent
acb265a5cc
commit
9df1ac5dd9
1 changed files with 11 additions and 7 deletions
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@ -1833,13 +1833,12 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
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if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
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goto out;
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features = uffdio_api.features;
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if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) {
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memset(&uffdio_api, 0, sizeof(uffdio_api));
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if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
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goto out;
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ret = -EINVAL;
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goto out;
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}
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ret = -EINVAL;
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if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
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goto err_out;
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ret = -EPERM;
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if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
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goto err_out;
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/* report all available features and ioctls to userland */
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uffdio_api.features = UFFD_API_FEATURES;
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uffdio_api.ioctls = UFFD_API_IOCTLS;
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@ -1852,6 +1851,11 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
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ret = 0;
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out:
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return ret;
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err_out:
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memset(&uffdio_api, 0, sizeof(uffdio_api));
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if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
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ret = -EFAULT;
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goto out;
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}
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static long userfaultfd_ioctl(struct file *file, unsigned cmd,
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