TL;DR: NACK because you sent two conflicting non-RFC patches as
'alternatives', which is not how development on-list works. Please resend
maybe one of these as an RFC...
+Al into this as he is the author of commit 8b3ec6814c83.
On Wed, Sep 25, 2024 at 04:16:28PM GMT, Shu Han wrote:
> This patch moves the security_file_mmap() back into do_mmap(), which
> revert the commit 8b3ec6814c83d76b85bd13badc48552836c24839
> ("take security_mmap_file() outside of ->mmap_sem"). Below is the reason.
Nit - we typically use the short version of the commit hash when
referencing a commit, so this would be commit 8b3ec6814c83.
Also if this is a revert this should be reflected in the subject... and
presumably given the original patch is from 2012 it's not a revert at all?
>
> Some logic may call do_mmap() without calling security_file_mmap(),
> without being aware of the harm this poses to LSM.
'Some logic'? Which?
There's no security_file_mmap() function in the kernel? You mean
security_mmap_file()? You're attempting to do something pretty major here,
so while this is obviously a typo it's pretty important you get these
details right :)
>
> For example, CVE-2016-10044[1] has reported many years ago, but the
> remap_file_pages() can still bypass the W^X policy enforced by SELinux[2]
> for a long time.
>
> Add a check is easy, but there may have more calls to do_mmap() in the
> future. Moving security_file_mmap() back into do_mmap() can avoid
> forgetting, and avoid repeated logic for whether READ_IMPLIES_EXEC should
> add PROT_EXEC for the mapping or not(In current, the !MMU case won't
> imply exec if the file's mmap_capabilities is not exist, but the
> security check logic is different).
But we might want to do things internal to the kernel that don't require
this check? Drivers can map too - the only place we need to be doing the
security check is in the user-facing mmap syscall.
If something is added that calls do_mmap() without proper security checks -
that's a bug in _that_ interface.
So I disagree with this patch as a whole.
Keep in mind we _do_ perform a security-hooked free memory check in the
mmap logic security_vm_enough_memory_mm(), so it isn't as if everything is
bypassed, only this security_mmap_file() function.
Which is surely only applicable in instances of user-facing API so is... in
the right place now?
Yeah I am not convinced on any level.
>
> It is noteworthy that moving the security check in do_mmap() will let it
> in the mmap_write_lock, which slows down the performance and even have
> deadlocks if someone depends on it(Since security_file_mprotect() is
> already in the lock, this possibility is tiny).
Err what? We can't accept a patch that might deadlock even if you claim the
possibility is 'tiny'... that's a NACK in itself. You _have_ to demonstrate
that you aren't deadlocking, this isn't optional.
>
> Link: https://project-zero.issues.chromium.org/issues/42452389 [1]
> Link: https://lore.kernel.org/all/20240919080905.4506-2-paul@xxxxxxxxxxxxxx/ [2]
> Signed-off-by: Shu Han <ebpqwerty472123@xxxxxxxxx>
You need to have a fixes tag here for Al's patch presumably.
> ---
> An alternative method is moving the check of READ_IMPLIES_EXEC out of
> do_mmap() and calling the LSM hooks at the same time, which has better
> performance and compatibility but may introduce some complexity. It has
> been proposed in [3], which cannot be applied at the same time with
> this patch.
> Link: https://lore.kernel.org/all/20240925063034.169-1-ebpqwerty472123@xxxxxxxxx/ [3]
You can't send multiple conflicting non-RFC patches at once... that's
completely ridiculous.
NACK, and re-send one of these as an RFC perhaps referencing the other as
an alternative?
> ---
> include/linux/security.h | 8 ++++----
> ipc/shm.c | 4 ----
> mm/mmap.c | 9 +++++----
> mm/nommu.c | 5 ++++-
> mm/util.c | 19 ++++++++-----------
> security/security.c | 41 ++++------------------------------------
> 6 files changed, 25 insertions(+), 61 deletions(-)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index c37c32ebbdcd..e061bc9a0331 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -423,8 +423,8 @@ void security_file_free(struct file *file);
> int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
> int security_file_ioctl_compat(struct file *file, unsigned int cmd,
> unsigned long arg);
> -int security_mmap_file(struct file *file, unsigned long prot,
> - unsigned long flags);
> +int security_mmap_file(struct file *file, unsigned long reqprot,
> + unsigned long prot, unsigned long flags);
> int security_mmap_addr(unsigned long addr);
> int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> unsigned long prot);
> @@ -1077,8 +1077,8 @@ static inline int security_file_ioctl_compat(struct file *file,
> return 0;
> }
>
> -static inline int security_mmap_file(struct file *file, unsigned long prot,
> - unsigned long flags)
> +static inline int security_mmap_file(struct file *file, unsigned long reqprot,
> + unsigned long prot, unsigned long flags)
> {
> return 0;
> }
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 3e3071252dac..ce02560b856f 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -1636,10 +1636,6 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
> sfd->vm_ops = NULL;
> file->private_data = sfd;
>
> - err = security_mmap_file(file, prot, flags);
> - if (err)
> - goto out_fput;
> -
> if (mmap_write_lock_killable(current->mm)) {
> err = -EINTR;
> goto out_fput;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 18fddcce03b8..56f9520f85ab 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1260,6 +1260,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> int pkey = 0;
> + unsigned long reqprot = prot, err;
>
> *populate = 0;
>
> @@ -1276,6 +1277,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
> if (!(file && path_noexec(&file->f_path)))
> prot |= PROT_EXEC;
>
> + err = security_mmap_file(file, reqprot, prot, flags);
> + if (err)
> + return err;
> +
> /* force arch specific MAP_FIXED handling in get_unmapped_area */
> if (flags & MAP_FIXED_NOREPLACE)
> flags |= MAP_FIXED;
> @@ -3198,12 +3203,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> flags |= MAP_LOCKED;
>
> file = get_file(vma->vm_file);
> - ret = security_mmap_file(vma->vm_file, prot, flags);
> - if (ret)
> - goto out_fput;
> ret = do_mmap(vma->vm_file, start, size,
> prot, flags, 0, pgoff, &populate, NULL);
> -out_fput:
> fput(file);
> out:
> mmap_write_unlock(mm);
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 7296e775e04e..e632f3105a5a 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -681,7 +681,7 @@ static int validate_mmap_request(struct file *file,
> unsigned long pgoff,
> unsigned long *_capabilities)
> {
> - unsigned long capabilities, rlen;
> + unsigned long capabilities, rlen, reqprot = prot;
> int ret;
>
> /* do the simple checks first */
> @@ -818,6 +818,9 @@ static int validate_mmap_request(struct file *file,
> }
>
> /* allow the security API to have its say */
> + ret = security_mmap_file(file, reqprot, prot, flags);
> + if (ret < 0)
> + return ret;
> ret = security_mmap_addr(addr);
> if (ret < 0)
> return ret;
> diff --git a/mm/util.c b/mm/util.c
> index bd283e2132e0..47345e927a8f 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -581,17 +581,14 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
> unsigned long populate;
> LIST_HEAD(uf);
>
> - ret = security_mmap_file(file, prot, flag);
> - if (!ret) {
> - if (mmap_write_lock_killable(mm))
> - return -EINTR;
> - ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
> - &uf);
> - mmap_write_unlock(mm);
> - userfaultfd_unmap_complete(mm, &uf);
> - if (populate)
> - mm_populate(ret, populate);
> - }
> + if (mmap_write_lock_killable(mm))
> + return -EINTR;
> + ret = do_mmap(file, addr, len, prot, flag, 0, pgoff, &populate,
> + &uf);
> + mmap_write_unlock(mm);
> + userfaultfd_unmap_complete(mm, &uf);
> + if (populate)
> + mm_populate(ret, populate);
> return ret;
> }
>
> diff --git a/security/security.c b/security/security.c
> index 4564a0a1e4ef..25556629f588 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2927,42 +2927,10 @@ int security_file_ioctl_compat(struct file *file, unsigned int cmd,
> }
> EXPORT_SYMBOL_GPL(security_file_ioctl_compat);
>
> -static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
> -{
> - /*
> - * Does we have PROT_READ and does the application expect
> - * it to imply PROT_EXEC? If not, nothing to talk about...
> - */
> - if ((prot & (PROT_READ | PROT_EXEC)) != PROT_READ)
> - return prot;
> - if (!(current->personality & READ_IMPLIES_EXEC))
> - return prot;
> - /*
> - * if that's an anonymous mapping, let it.
> - */
> - if (!file)
> - return prot | PROT_EXEC;
> - /*
> - * ditto if it's not on noexec mount, except that on !MMU we need
> - * NOMMU_MAP_EXEC (== VM_MAYEXEC) in this case
> - */
> - if (!path_noexec(&file->f_path)) {
> -#ifndef CONFIG_MMU
> - if (file->f_op->mmap_capabilities) {
> - unsigned caps = file->f_op->mmap_capabilities(file);
> - if (!(caps & NOMMU_MAP_EXEC))
> - return prot;
> - }
> -#endif
> - return prot | PROT_EXEC;
> - }
> - /* anything on noexec mount won't get PROT_EXEC */
> - return prot;
> -}
> -
Err.... why are we removing all of this??
> /**
> * security_mmap_file() - Check if mmap'ing a file is allowed
> * @file: file
> + * @reqprot: protection requested by user
> * @prot: protection applied by the kernel
> * @flags: flags
> *
> @@ -2971,11 +2939,10 @@ static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
> *
> * Return: Returns 0 if permission is granted.
> */
> -int security_mmap_file(struct file *file, unsigned long prot,
> - unsigned long flags)
> +int security_mmap_file(struct file *file, unsigned long reqprot,
> + unsigned long prot, unsigned long flags)
> {
> - return call_int_hook(mmap_file, file, prot, mmap_prot(file, prot),
> - flags);
> + return call_int_hook(mmap_file, file, reqprot, prot, flags);
> }
>
> /**
>
> base-commit: f89722faa31466ff41aed21bdeb9cf34c2312858
> --
> 2.34.1
>
