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| author | Jann Horn <jannh@google.com> | 2019-07-04 21:44:44 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-10-07 19:55:22 +0300 |
| commit | ca2cf05447866c4653243bfe3ce4d1114eaee953 (patch) | |
| tree | d513eb442fa3e516422bac718fd2136c04bb1feb | |
| parent | c8a9950f1b3a400b3eabe55f686e38fa2086af40 (diff) | |
| download | linux-ca2cf05447866c4653243bfe3ce4d1114eaee953.tar.xz | |
Smack: Don't ignore other bprm->unsafe flags if LSM_UNSAFE_PTRACE is set
commit 3675f052b43ba51b99b85b073c7070e083f3e6fb upstream.
There is a logic bug in the current smack_bprm_set_creds():
If LSM_UNSAFE_PTRACE is set, but the ptrace state is deemed to be
acceptable (e.g. because the ptracer detached in the meantime), the other
->unsafe flags aren't checked. As far as I can tell, this means that
something like the following could work (but I haven't tested it):
- task A: create task B with fork()
- task B: set NO_NEW_PRIVS
- task B: install a seccomp filter that makes open() return 0 under some
conditions
- task B: replace fd 0 with a malicious library
- task A: attach to task B with PTRACE_ATTACH
- task B: execve() a file with an SMACK64EXEC extended attribute
- task A: while task B is still in the middle of execve(), exit (which
destroys the ptrace relationship)
Make sure that if any flags other than LSM_UNSAFE_PTRACE are set in
bprm->unsafe, we reject the execve().
Cc: stable@vger.kernel.org
Fixes: 5663884caab1 ("Smack: unify all ptrace accesses in the smack")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | security/smack/smack_lsm.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 09119c43525e..ddcda41842f1 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -944,7 +944,8 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm) if (rc != 0) return rc; - } else if (bprm->unsafe) + } + if (bprm->unsafe & ~LSM_UNSAFE_PTRACE) return -EPERM; bsp->smk_task = isp->smk_task; |