[PATCH 5/6] shmem: add sealing support to hugetlb-backed memfd

[Marc-Andrà Lureau]

Adapt add_seals()/get_seals() to work with hugetbfs-backed memory.

Teach memfd_create() to allow sealing operations on MFD_HUGETLB.

Signed-off-by: Marc-Andrà Lureau <marcandre.lureau@xxxxxxxxxx>
---
 mm/shmem.c | 51 ++++++++++++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 21 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b7811979611f..b7c59d993c19 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2717,6 +2717,19 @@ static int shmem_wait_for_pins(struct address_space *mapping)
 	return error;
 }
 
+static unsigned int *memfd_get_seals(struct file *file)
+{
+	if (file->f_op == &shmem_file_operations)
+		return &SHMEM_I(file_inode(file))->seals;
+
+#ifdef CONFIG_HUGETLBFS
+	if (file->f_op == &hugetlbfs_file_operations)
+		return &HUGETLBFS_I(file_inode(file))->seals;
+#endif
+
+	return NULL;
+}
+
 #define F_ALL_SEALS (F_SEAL_SEAL | \
 		     F_SEAL_SHRINK | \
 		     F_SEAL_GROW | \
@@ -2725,7 +2738,7 @@ static int shmem_wait_for_pins(struct address_space *mapping)
 static int memfd_add_seals(struct file *file, unsigned int seals)
 {
 	struct inode *inode = file_inode(file);
-	struct shmem_inode_info *info = SHMEM_I(inode);
+	unsigned int *file_seals;
 	int error;
 
 	/*
@@ -2758,8 +2771,6 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 	 * other file types.
 	 */
 
-	if (file->f_op != &shmem_file_operations)
-		return -EINVAL;
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EPERM;
 	if (seals & ~(unsigned int)F_ALL_SEALS)
@@ -2767,12 +2778,18 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 
 	inode_lock(inode);
 
-	if (info->seals & F_SEAL_SEAL) {
+	file_seals = memfd_get_seals(file);
+	if (!file_seals) {
+		error = -EINVAL;
+		goto unlock;
+	}
+
+	if (*file_seals & F_SEAL_SEAL) {
 		error = -EPERM;
 		goto unlock;
 	}
 
-	if ((seals & F_SEAL_WRITE) && !(info->seals & F_SEAL_WRITE)) {
+	if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
 		error = mapping_deny_writable(file->f_mapping);
 		if (error)
 			goto unlock;
@@ -2784,7 +2801,7 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 		}
 	}
 
-	info->seals |= seals;
+	*file_seals |= seals;
 	error = 0;
 
 unlock:
@@ -2792,12 +2809,11 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 	return error;
 }
 
-static int memfd_get_seals(struct file *file)
+static int memfd_fcntl_get_seals(struct file *file)
 {
-	if (file->f_op != &shmem_file_operations)
-		return -EINVAL;
+	unsigned int *seals = memfd_get_seals(file);
 
-	return SHMEM_I(file_inode(file))->seals;
+	return seals ? *seals : -EINVAL;
 }
 
 long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
@@ -2813,7 +2829,7 @@ long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 		error = memfd_add_seals(file, arg);
 		break;
 	case F_GET_SEALS:
-		error = memfd_get_seals(file);
+		error = memfd_fcntl_get_seals(file);
 		break;
 	default:
 		error = -EINVAL;
@@ -3657,7 +3673,7 @@ SYSCALL_DEFINE2(memfd_create,
 		const char __user *, uname,
 		unsigned int, flags)
 {
-	struct shmem_inode_info *info;
+	unsigned int *file_seals;
 	struct file *file;
 	int fd, error;
 	char *name;
@@ -3667,9 +3683,6 @@ SYSCALL_DEFINE2(memfd_create,
 		if (flags & ~(unsigned int)MFD_ALL_FLAGS)
 			return -EINVAL;
 	} else {
-		/* Sealing not supported in hugetlbfs (MFD_HUGETLB) */
-		if (flags & MFD_ALLOW_SEALING)
-			return -EINVAL;
 		/* Allow huge page size encoding in flags. */
 		if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
 				(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
@@ -3722,12 +3735,8 @@ SYSCALL_DEFINE2(memfd_create,
 	file->f_flags |= O_RDWR | O_LARGEFILE;
 
 	if (flags & MFD_ALLOW_SEALING) {
-		/*
-		 * flags check at beginning of function ensures
-		 * this is not a hugetlbfs (MFD_HUGETLB) file.
-		 */
-		info = SHMEM_I(file_inode(file));
-		info->seals &= ~F_SEAL_SEAL;
+		file_seals = memfd_get_seals(file);
+		*file_seals &= ~F_SEAL_SEAL;
 	}
 
 	fd_install(fd, file);
-- 
2.15.0.rc0.40.gaefcc5f6f