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Subject[PATCH 5.2 130/137] Smack: Dont ignore other bprm->unsafe flags if LSM_UNSAFE_PTRACE is set
From: Jann Horn <>

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
- 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().

Fixes: 5663884caab1 ("Smack: unify all ptrace accesses in the smack")
Signed-off-by: Jann Horn <>
Signed-off-by: Casey Schaufler <>
Signed-off-by: Greg Kroah-Hartman <>

security/smack/smack_lsm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -937,7 +937,8 @@ static int smack_bprm_set_creds(struct l

if (rc != 0)
return rc;
- } else if (bprm->unsafe)
+ }
+ if (bprm->unsafe & ~LSM_UNSAFE_PTRACE)
return -EPERM;

bsp->smk_task = isp->smk_task;

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