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authorJordy Zomer <jordy@jordyzomer.github.io>2021-09-07 19:56:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-09-08 11:50:24 -0700
commit110860541f443f950c1274f217a1a3e298670a33 (patch)
treea4210a0c80f3793e0ac66806cc2e56ed6d9e2a86 /mm/secretmem.c
parent41c961b9013ee9b6d0491f6926df546e37964b1f (diff)
mm/secretmem: use refcount_t instead of atomic_t
When a secret memory region is active, memfd_secret disables hibernation. One of the goals is to keep the secret data from being written to persistent-storage. It accomplishes this by maintaining a reference count to `secretmem_users`. Once this reference is held your system can not be hibernated due to the check in `hibernation_available()`. However, because `secretmem_users` is of type `atomic_t`, reference counter overflows are possible. As you can see there's an `atomic_inc` for each `memfd` that is opened in the `memfd_secret` syscall. If a local attacker succeeds to open 2^32 memfd's, the counter will wrap around to 0. This implies that you may hibernate again, even though there are still regions of this secret memory, thereby bypassing the security check. In an attempt to fix this I have used `refcount_t` instead of `atomic_t` which prevents reference counter overflows. Link: https://lkml.kernel.org/r/20210820043339.2151352-1-jordy@pwning.systems Signed-off-by: Jordy Zomer <jordy@pwning.systems> Cc: Kees Cook <keescook@chromium.org>, Cc: Jordy Zomer <jordy@jordyzomer.github.io> Cc: James Bottomley <James.Bottomley@HansenPartnership.com> Cc: Mike Rapoport <rppt@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/secretmem.c')
-rw-r--r--mm/secretmem.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/mm/secretmem.c b/mm/secretmem.c
index 030f02ddc7c1..1fea68b8d5a6 100644
--- a/mm/secretmem.c
+++ b/mm/secretmem.c
@@ -18,6 +18,7 @@
#include <linux/secretmem.h>
#include <linux/set_memory.h>
#include <linux/sched/signal.h>
+#include <linux/refcount.h>
#include <uapi/linux/magic.h>
@@ -40,11 +41,11 @@ module_param_named(enable, secretmem_enable, bool, 0400);
MODULE_PARM_DESC(secretmem_enable,
"Enable secretmem and memfd_secret(2) system call");
-static atomic_t secretmem_users;
+static refcount_t secretmem_users;
bool secretmem_active(void)
{
- return !!atomic_read(&secretmem_users);
+ return !!refcount_read(&secretmem_users);
}
static vm_fault_t secretmem_fault(struct vm_fault *vmf)
@@ -103,7 +104,7 @@ static const struct vm_operations_struct secretmem_vm_ops = {
static int secretmem_release(struct inode *inode, struct file *file)
{
- atomic_dec(&secretmem_users);
+ refcount_dec(&secretmem_users);
return 0;
}
@@ -217,7 +218,7 @@ SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
file->f_flags |= O_LARGEFILE;
fd_install(fd, file);
- atomic_inc(&secretmem_users);
+ refcount_inc(&secretmem_users);
return fd;
err_put_fd: