diff options
| author | Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> | 2015-10-20 16:09:19 +0200 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2015-10-27 16:12:35 -0500 |
| commit | f2ca379642d7a843be972ea4167abdd3c8c9e5d1 (patch) | |
| tree | 03d03e85a7e38cb732fe09d2ca85baec3bc815d5 | |
| parent | 6ff33f3902c3b1c5d0db6b1e2c70b6d76fba357f (diff) | |
namei: permit linking with CAP_FOWNER in userns
Attempting to hardlink to an unsafe file (e.g. a setuid binary) from
within an unprivileged user namespace fails, even if CAP_FOWNER is held
within the namespace. This may cause various failures, such as a gentoo
installation within a lxc container failing to build and install specific
packages.
This change permits hardlinking of files owned by mapped uids, if
CAP_FOWNER is held for that namespace. Furthermore, it improves consistency
by using the existing inode_owner_or_capable(), which is aware of
namespaced capabilities as of 23adbe12ef7d3 ("fs,userns: Change
inode_capable to capable_wrt_inode_uidgid").
Signed-off-by: Dirk Steinmetz <public@rsjtdrjgfuzkfg.com>
This is hitting us in Ubuntu during some dpkg upgrades in containers.
When upgrading a file dpkg creates a hard link to the old file to back
it up before overwriting it. When packages upgrade suid files owned by a
non-root user the link isn't permitted, and the package upgrade fails.
This patch fixes our problem.
Tested-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
| -rw-r--r-- | fs/namei.c | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/fs/namei.c b/fs/namei.c index 726d211db484..29fc6a657477 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -955,26 +955,23 @@ static bool safe_hardlink_source(struct inode *inode) * - sysctl_protected_hardlinks enabled * - fsuid does not match inode * - hardlink source is unsafe (see safe_hardlink_source() above) - * - not CAP_FOWNER + * - not CAP_FOWNER in a namespace with the inode owner uid mapped * * Returns 0 if successful, -ve on error. */ static int may_linkat(struct path *link) { - const struct cred *cred; struct inode *inode; if (!sysctl_protected_hardlinks) return 0; - cred = current_cred(); inode = link->dentry->d_inode; /* Source inode owner (or CAP_FOWNER) can hardlink all they like, * otherwise, it must be a safe source. */ - if (uid_eq(cred->fsuid, inode->i_uid) || safe_hardlink_source(inode) || - capable(CAP_FOWNER)) + if (inode_owner_or_capable(inode) || safe_hardlink_source(inode)) return 0; audit_log_link_denied("linkat", link); |