core dump: remain dumpable
The coredump code always calls set_dumpable(0) when it starts (even
if RLIMIT_CORE prevents any core from being dumped). The effect of
this (via task_dumpable) is to make /proc/pid/* files owned by root
instead of the user, so the user can no longer examine his own
process--in a case where there was never any privileged data to
protect. This affects e.g. auxv, environ, fd; in Fedora (execshield)
kernels, also maps. In practice, you can only notice this when a
debugger has requested PTRACE_EVENT_EXIT tracing.
set_dumpable was only used in do_coredump for synchronization and not
intended for any security purpose. (It doesn't secure anything that wasn't
already unsecured when a process dies by SIGTERM instead of SIGQUIT.)
This changes do_coredump to check the core_waiters count as the means of
synchronization, which is sufficient. Now we leave the "dumpable" bits alone.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/exec.c b/fs/exec.c
index 2c942e2..4ccaaa4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1692,7 +1692,10 @@
if (!binfmt || !binfmt->core_dump)
goto fail;
down_write(&mm->mmap_sem);
- if (!get_dumpable(mm)) {
+ /*
+ * If another thread got here first, or we are not dumpable, bail out.
+ */
+ if (mm->core_waiters || !get_dumpable(mm)) {
up_write(&mm->mmap_sem);
goto fail;
}
@@ -1706,7 +1709,6 @@
flag = O_EXCL; /* Stop rewrite attacks */
current->fsuid = 0; /* Dump root private */
}
- set_dumpable(mm, 0);
retval = coredump_wait(exit_code);
if (retval < 0)