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Code Issues Releases Wiki Activity

mm: update memfd seal write check to include F_SEAL_WRITE

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From: Lorenzo Stoakes <lstoakes@gmail.com>

[ Upstream commit 28464bbb2d ]

The seal_check_future_write() function is called by shmem_mmap() or
hugetlbfs_file_mmap() to disallow any future writable mappings of an memfd
sealed this way.

The F_SEAL_WRITE flag is not checked here, as that is handled via the
mapping->i_mmap_writable mechanism and so any attempt at a mapping would
fail before this could be run.

However we intend to change this, meaning this check can be performed for
F_SEAL_WRITE mappings also.

The logic here is equally applicable to both flags, so update this
function to accommodate both and rename it accordingly.

Link: https://lkml.kernel.org/r/913628168ce6cce77df7d13a63970bae06a526e0.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Isaac J. Manjarres 2025-07-29 18:51:46 -07:00 committed by Greg Kroah-Hartman
parent 17c5d49beb
commit 87a75f68ea
3 changed files with 10 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/hugetlbfs/inode.c
View File

@ -136,7 +136,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND); vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND);
vma->vm_ops = &hugetlb_vm_ops; vma->vm_ops = &hugetlb_vm_ops;
ret = seal_check_future_write(info->seals, vma); ret = seal_check_write(info->seals, vma);
if (ret) if (ret)
return ret; return ret;

15
include/linux/mm.h
View File

@ -4023,25 +4023,26 @@ static inline void mem_dump_obj(void *object) {}
#endif #endif
/** /**
* seal_check_future_write - Check for F_SEAL_FUTURE_WRITE flag and handle it * seal_check_write - Check for F_SEAL_WRITE or F_SEAL_FUTURE_WRITE flags and
* handle them.
* @seals: the seals to check * @seals: the seals to check
* @vma: the vma to operate on * @vma: the vma to operate on
* *
* Check whether F_SEAL_FUTURE_WRITE is set; if so, do proper check/handling on * Check whether F_SEAL_WRITE or F_SEAL_FUTURE_WRITE are set; if so, do proper
* the vma flags. Return 0 if check pass, or <0 for errors. * check/handling on the vma flags. Return 0 if check pass, or <0 for errors.
*/ */
static inline int seal_check_future_write(int seals, struct vm_area_struct *vma) static inline int seal_check_write(int seals, struct vm_area_struct *vma)
{ {
if (seals & F_SEAL_FUTURE_WRITE) { if (seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
/* /*
* New PROT_WRITE and MAP_SHARED mmaps are not allowed when * New PROT_WRITE and MAP_SHARED mmaps are not allowed when
* "future write" seal active. * write seals are active.
*/ */
if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE)) if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
return -EPERM; return -EPERM;
/* /*
* Since an F_SEAL_FUTURE_WRITE sealed memfd can be mapped as * Since an F_SEAL_[FUTURE_]WRITE sealed memfd can be mapped as
* MAP_SHARED and read-only, take care to not allow mprotect to * MAP_SHARED and read-only, take care to not allow mprotect to
* revert protections on such mappings. Do this only for shared * revert protections on such mappings. Do this only for shared
* mappings. For private mappings, don't need to mask * mappings. For private mappings, don't need to mask

2
mm/shmem.c
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@ -2396,7 +2396,7 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
struct shmem_inode_info *info = SHMEM_I(inode); struct shmem_inode_info *info = SHMEM_I(inode);
int ret; int ret;
ret = seal_check_future_write(info->seals, vma); ret = seal_check_write(info->seals, vma);
if (ret) if (ret)
return ret; return ret;