Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: > On Thu, Nov 17, 2016 at 9:08 AM, Eric W. Biederman > <ebiederm@xxxxxxxxxxxx> wrote: >> >> It is the reasonable expectation that if an executable file is not >> readable there will be no way for a user without special privileges to >> read the file. This is enforced in ptrace_attach but if we are >> already attached there is no enforcement if a readonly executable >> is exec'd. >> >> Therefore do the simple thing and if there is a non-dumpable >> executable that we are tracing without privilege fail to exec it. >> >> Fixes: v1.0 >> Cc: stable@xxxxxxxxxxxxxxx >> Reported-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> >> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> >> --- >> fs/exec.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/fs/exec.c b/fs/exec.c >> index fdec760bfac3..de107f74e055 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -1230,6 +1230,11 @@ int flush_old_exec(struct linux_binprm * bprm) >> { >> int retval; >> >> + /* Fail if the tracer can't read the executable */ >> + if ((bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP) && >> + !ptracer_capable(current, bprm->mm->user_ns)) >> + return -EPERM; >> + > > At the very least, I think that BINPRM_FLAGS_ENFORCE_NONDUMP needs to > check capable_wrt_inode_uidgid too. Otherwise we risk breaking: > > $ gcc whatever.c > $ chmod 400 a.out > $ strace a.out It is an invariant that if you have caps in mm->user_ns you will also be capable_write_inode_uidgid of all files that a process exec's. My third patch winds up changing mm->user_ns to maintain this invariant. It is also true that Willy convinced me while this check is trivial it will break historic uses so I have replaced this patch with: "ptrace: Don't allow accessing an undumpable mm. Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>