76 lines
2.6 KiB
Diff
76 lines
2.6 KiB
Diff
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From 5506202b83e65b844309093e712b5b507eb1e403 Mon Sep 17 00:00:00 2001
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From: Jann Horn <jannh@google.com>
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Date: Tue, 13 Nov 2018 07:42:38 +0000
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Subject: [PATCH 09/11] userns: also map extents in the reverse map to kernel
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IDs
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BugLink: https://launchpad.net/bugs/1801924
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The current logic first clones the extent array and sorts both copies, then
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maps the lower IDs of the forward mapping into the lower namespace, but
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doesn't map the lower IDs of the reverse mapping.
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This means that code in a nested user namespace with >5 extents will see
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incorrect IDs. It also breaks some access checks, like
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inode_owner_or_capable() and privileged_wrt_inode_uidgid(), so a process
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can incorrectly appear to be capable relative to an inode.
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To fix it, we have to make sure that the "lower_first" members of extents
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in both arrays are translated; and we have to make sure that the reverse
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map is sorted *after* the translation (since otherwise the translation can
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break the sorting).
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This is CVE-2018-18955.
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Fixes: 6397fac4915a ("userns: bump idmap limits to 340")
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Cc: stable@vger.kernel.org
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Signed-off-by: Jann Horn <jannh@google.com>
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Tested-by: Eric W. Biederman <ebiederm@xmission.com>
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Reviewed-by: Eric W. Biederman <ebiederm@xmission.com>
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Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
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CVE-2018-18955
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(cherry picked from commit d2f007dbe7e4c9583eea6eb04d60001e85c6f1bd)
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Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
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Acked-by: Colin King <colin.king@canonical.com>
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Acked-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
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Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
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---
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kernel/user_namespace.c | 12 ++++++++----
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1 file changed, 8 insertions(+), 4 deletions(-)
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diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
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index 08d638386b83..12de8c144db9 100644
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--- a/kernel/user_namespace.c
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+++ b/kernel/user_namespace.c
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@@ -983,10 +983,6 @@ static ssize_t map_write(struct file *file, const char __user *buf,
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if (!new_idmap_permitted(file, ns, cap_setid, &new_map))
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goto out;
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- ret = sort_idmaps(&new_map);
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- if (ret < 0)
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- goto out;
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-
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ret = -EPERM;
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/* Map the lower ids from the parent user namespace to the
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* kernel global id space.
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@@ -1013,6 +1009,14 @@ static ssize_t map_write(struct file *file, const char __user *buf,
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e->lower_first = lower_first;
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}
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+ /*
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+ * If we want to use binary search for lookup, this clones the extent
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+ * array and sorts both copies.
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+ */
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+ ret = sort_idmaps(&new_map);
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+ if (ret < 0)
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+ goto out;
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+
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/* Install the map */
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if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) {
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memcpy(map->extent, new_map.extent,
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--
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2.11.0
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