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d7c9e99aee
The rlimit counter is tied to uid in the user_namespace. This allows rlimit values to be specified in userns even if they are already globally exceeded by the user. However, the value of the previous user_namespaces cannot be exceeded. Changelog v11: * Fix issue found by lkp robot. v8: * Fix issues found by lkp-tests project. v7: * Keep only ucounts for RLIMIT_MEMLOCK checks instead of struct cred. v6: * Fix bug in hugetlb_file_setup() detected by trinity. Reported-by: kernel test robot <oliver.sang@intel.com> Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Alexey Gladkov <legion@kernel.org> Link: https://lkml.kernel.org/r/970d50c70c71bfd4496e0e8d2a0a32feebebb350.1619094428.git.legion@kernel.org Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
330 lines
7.9 KiB
C
330 lines
7.9 KiB
C
/*
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* memfd_create system call and file sealing support
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*
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* Code was originally included in shmem.c, and broken out to facilitate
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* use by hugetlbfs as well as tmpfs.
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*
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* This file is released under the GPL.
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*/
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#include <linux/fs.h>
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#include <linux/vfs.h>
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#include <linux/pagemap.h>
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#include <linux/file.h>
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#include <linux/mm.h>
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#include <linux/sched/signal.h>
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#include <linux/khugepaged.h>
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#include <linux/syscalls.h>
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#include <linux/hugetlb.h>
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#include <linux/shmem_fs.h>
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#include <linux/memfd.h>
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#include <uapi/linux/memfd.h>
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/*
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* We need a tag: a new tag would expand every xa_node by 8 bytes,
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* so reuse a tag which we firmly believe is never set or cleared on tmpfs
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* or hugetlbfs because they are memory only filesystems.
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*/
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#define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE
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#define LAST_SCAN 4 /* about 150ms max */
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static void memfd_tag_pins(struct xa_state *xas)
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{
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struct page *page;
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unsigned int tagged = 0;
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lru_add_drain();
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xas_lock_irq(xas);
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xas_for_each(xas, page, ULONG_MAX) {
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if (xa_is_value(page))
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continue;
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page = find_subpage(page, xas->xa_index);
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if (page_count(page) - page_mapcount(page) > 1)
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xas_set_mark(xas, MEMFD_TAG_PINNED);
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if (++tagged % XA_CHECK_SCHED)
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continue;
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xas_pause(xas);
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xas_unlock_irq(xas);
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cond_resched();
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xas_lock_irq(xas);
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}
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xas_unlock_irq(xas);
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}
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/*
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* Setting SEAL_WRITE requires us to verify there's no pending writer. However,
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* via get_user_pages(), drivers might have some pending I/O without any active
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* user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
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* and see whether it has an elevated ref-count. If so, we tag them and wait for
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* them to be dropped.
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* The caller must guarantee that no new user will acquire writable references
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* to those pages to avoid races.
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*/
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static int memfd_wait_for_pins(struct address_space *mapping)
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{
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XA_STATE(xas, &mapping->i_pages, 0);
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struct page *page;
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int error, scan;
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memfd_tag_pins(&xas);
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error = 0;
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for (scan = 0; scan <= LAST_SCAN; scan++) {
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unsigned int tagged = 0;
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if (!xas_marked(&xas, MEMFD_TAG_PINNED))
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break;
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if (!scan)
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lru_add_drain_all();
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else if (schedule_timeout_killable((HZ << scan) / 200))
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scan = LAST_SCAN;
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xas_set(&xas, 0);
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xas_lock_irq(&xas);
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xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
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bool clear = true;
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if (xa_is_value(page))
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continue;
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page = find_subpage(page, xas.xa_index);
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if (page_count(page) - page_mapcount(page) != 1) {
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/*
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* On the last scan, we clean up all those tags
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* we inserted; but make a note that we still
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* found pages pinned.
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*/
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if (scan == LAST_SCAN)
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error = -EBUSY;
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else
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clear = false;
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}
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if (clear)
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xas_clear_mark(&xas, MEMFD_TAG_PINNED);
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if (++tagged % XA_CHECK_SCHED)
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continue;
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xas_pause(&xas);
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xas_unlock_irq(&xas);
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cond_resched();
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xas_lock_irq(&xas);
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}
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xas_unlock_irq(&xas);
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}
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return error;
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}
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static unsigned int *memfd_file_seals_ptr(struct file *file)
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{
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if (shmem_file(file))
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return &SHMEM_I(file_inode(file))->seals;
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#ifdef CONFIG_HUGETLBFS
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if (is_file_hugepages(file))
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return &HUGETLBFS_I(file_inode(file))->seals;
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#endif
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return NULL;
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}
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#define F_ALL_SEALS (F_SEAL_SEAL | \
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F_SEAL_SHRINK | \
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F_SEAL_GROW | \
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F_SEAL_WRITE | \
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F_SEAL_FUTURE_WRITE)
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static int memfd_add_seals(struct file *file, unsigned int seals)
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{
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struct inode *inode = file_inode(file);
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unsigned int *file_seals;
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int error;
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/*
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* SEALING
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* Sealing allows multiple parties to share a tmpfs or hugetlbfs file
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* but restrict access to a specific subset of file operations. Seals
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* can only be added, but never removed. This way, mutually untrusted
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* parties can share common memory regions with a well-defined policy.
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* A malicious peer can thus never perform unwanted operations on a
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* shared object.
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*
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* Seals are only supported on special tmpfs or hugetlbfs files and
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* always affect the whole underlying inode. Once a seal is set, it
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* may prevent some kinds of access to the file. Currently, the
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* following seals are defined:
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* SEAL_SEAL: Prevent further seals from being set on this file
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* SEAL_SHRINK: Prevent the file from shrinking
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* SEAL_GROW: Prevent the file from growing
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* SEAL_WRITE: Prevent write access to the file
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*
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* As we don't require any trust relationship between two parties, we
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* must prevent seals from being removed. Therefore, sealing a file
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* only adds a given set of seals to the file, it never touches
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* existing seals. Furthermore, the "setting seals"-operation can be
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* sealed itself, which basically prevents any further seal from being
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* added.
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*
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* Semantics of sealing are only defined on volatile files. Only
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* anonymous tmpfs and hugetlbfs files support sealing. More
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* importantly, seals are never written to disk. Therefore, there's
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* no plan to support it on other file types.
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*/
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if (!(file->f_mode & FMODE_WRITE))
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return -EPERM;
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if (seals & ~(unsigned int)F_ALL_SEALS)
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return -EINVAL;
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inode_lock(inode);
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file_seals = memfd_file_seals_ptr(file);
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if (!file_seals) {
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error = -EINVAL;
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goto unlock;
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}
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if (*file_seals & F_SEAL_SEAL) {
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error = -EPERM;
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goto unlock;
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}
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if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
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error = mapping_deny_writable(file->f_mapping);
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if (error)
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goto unlock;
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error = memfd_wait_for_pins(file->f_mapping);
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if (error) {
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mapping_allow_writable(file->f_mapping);
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goto unlock;
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}
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}
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*file_seals |= seals;
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error = 0;
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unlock:
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inode_unlock(inode);
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return error;
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}
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static int memfd_get_seals(struct file *file)
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{
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unsigned int *seals = memfd_file_seals_ptr(file);
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return seals ? *seals : -EINVAL;
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}
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long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
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{
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long error;
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switch (cmd) {
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case F_ADD_SEALS:
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/* disallow upper 32bit */
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if (arg > UINT_MAX)
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return -EINVAL;
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error = memfd_add_seals(file, arg);
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break;
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case F_GET_SEALS:
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error = memfd_get_seals(file);
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break;
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default:
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error = -EINVAL;
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break;
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}
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return error;
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}
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#define MFD_NAME_PREFIX "memfd:"
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#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
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#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
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#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
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SYSCALL_DEFINE2(memfd_create,
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const char __user *, uname,
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unsigned int, flags)
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{
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unsigned int *file_seals;
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struct file *file;
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int fd, error;
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char *name;
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long len;
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if (!(flags & MFD_HUGETLB)) {
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if (flags & ~(unsigned int)MFD_ALL_FLAGS)
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return -EINVAL;
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} else {
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/* Allow huge page size encoding in flags. */
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if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
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(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
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return -EINVAL;
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}
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/* length includes terminating zero */
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len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
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if (len <= 0)
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return -EFAULT;
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if (len > MFD_NAME_MAX_LEN + 1)
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return -EINVAL;
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name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
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if (!name)
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return -ENOMEM;
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strcpy(name, MFD_NAME_PREFIX);
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if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
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error = -EFAULT;
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goto err_name;
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}
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/* terminating-zero may have changed after strnlen_user() returned */
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if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
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error = -EFAULT;
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goto err_name;
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}
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fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
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if (fd < 0) {
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error = fd;
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goto err_name;
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}
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if (flags & MFD_HUGETLB) {
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struct ucounts *ucounts = NULL;
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file = hugetlb_file_setup(name, 0, VM_NORESERVE, &ucounts,
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HUGETLB_ANONHUGE_INODE,
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(flags >> MFD_HUGE_SHIFT) &
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MFD_HUGE_MASK);
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} else
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file = shmem_file_setup(name, 0, VM_NORESERVE);
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if (IS_ERR(file)) {
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error = PTR_ERR(file);
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goto err_fd;
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}
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file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
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file->f_flags |= O_LARGEFILE;
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if (flags & MFD_ALLOW_SEALING) {
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file_seals = memfd_file_seals_ptr(file);
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*file_seals &= ~F_SEAL_SEAL;
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}
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fd_install(fd, file);
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kfree(name);
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return fd;
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err_fd:
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put_unused_fd(fd);
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err_name:
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kfree(name);
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return error;
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}
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