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linux
/
fs
/
backing-file.c
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Vinicius Costa Gomes
and
Amir Goldstein
fs/backing-file: Convert to revert/override_creds_light()
Nov 11, 2024
d06ffd6
·
Nov 11, 2024
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359 lines (289 loc) · 8.42 KB
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linux
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backing-file.c
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// SPDX-License-Identifier: GPL-2.0-only /* * Common helpers for stackable filesystems and backing files. * * Forked from fs/overlayfs/file.c. * * Copyright (C) 2017 Red Hat, Inc. * Copyright (C) 2023 CTERA Networks. */ #include <linux/fs.h> #include <linux/backing-file.h> #include <linux/splice.h> #include <linux/mm.h> #include "internal.h" /** * backing_file_open - open a backing file for kernel internal use * @user_path: path that the user reuqested to open * @flags: open flags * @real_path: path of the backing file * @cred: credentials for open * * Open a backing file for a stackable filesystem (e.g., overlayfs). * @user_path may be on the stackable filesystem and @real_path on the * underlying filesystem. In this case, we want to be able to return the * @user_path of the stackable filesystem. This is done by embedding the * returned file into a container structure that also stores the stacked * file's path, which can be retrieved using backing_file_user_path(). */ struct file *backing_file_open(const struct path *user_path, int flags, const struct path *real_path, const struct cred *cred) { struct file *f; int error; f = alloc_empty_backing_file(flags, cred); if (IS_ERR(f)) return f; path_get(user_path); *backing_file_user_path(f) = *user_path; error = vfs_open(real_path, f); if (error) { fput(f); f = ERR_PTR(error); } return f; } EXPORT_SYMBOL_GPL(backing_file_open); struct file *backing_tmpfile_open(const struct path *user_path, int flags, const struct path *real_parentpath, umode_t mode, const struct cred *cred) { struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt); struct file *f; int error; f = alloc_empty_backing_file(flags, cred); if (IS_ERR(f)) return f; path_get(user_path); *backing_file_user_path(f) = *user_path; error = vfs_tmpfile(real_idmap, real_parentpath, f, mode); if (error) { fput(f); f = ERR_PTR(error); } return f; } EXPORT_SYMBOL(backing_tmpfile_open); struct backing_aio { struct kiocb iocb; refcount_t ref; struct kiocb *orig_iocb; /* used for aio completion */ void (*end_write)(struct kiocb *iocb, ssize_t); struct work_struct work; long res; }; static struct kmem_cache *backing_aio_cachep; #define BACKING_IOCB_MASK \ (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND) static rwf_t iocb_to_rw_flags(int flags) { return (__force rwf_t)(flags & BACKING_IOCB_MASK); } static void backing_aio_put(struct backing_aio *aio) { if (refcount_dec_and_test(&aio->ref)) { fput(aio->iocb.ki_filp); kmem_cache_free(backing_aio_cachep, aio); } } static void backing_aio_cleanup(struct backing_aio *aio, long res) { struct kiocb *iocb = &aio->iocb; struct kiocb *orig_iocb = aio->orig_iocb; orig_iocb->ki_pos = iocb->ki_pos; if (aio->end_write) aio->end_write(orig_iocb, res); backing_aio_put(aio); } static void backing_aio_rw_complete(struct kiocb *iocb, long res) { struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb); struct kiocb *orig_iocb = aio->orig_iocb; if (iocb->ki_flags & IOCB_WRITE) kiocb_end_write(iocb); backing_aio_cleanup(aio, res); orig_iocb->ki_complete(orig_iocb, res); } static void backing_aio_complete_work(struct work_struct *work) { struct backing_aio *aio = container_of(work, struct backing_aio, work); backing_aio_rw_complete(&aio->iocb, aio->res); } static void backing_aio_queue_completion(struct kiocb *iocb, long res) { struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb); /* * Punt to a work queue to serialize updates of mtime/size. */ aio->res = res; INIT_WORK(&aio->work, backing_aio_complete_work); queue_work(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq, &aio->work); } static int backing_aio_init_wq(struct kiocb *iocb) { struct super_block *sb = file_inode(iocb->ki_filp)->i_sb; if (sb->s_dio_done_wq) return 0; return sb_init_dio_done_wq(sb); } ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter, struct kiocb *iocb, int flags, struct backing_file_ctx *ctx) { struct backing_aio *aio = NULL; const struct cred *old_cred; ssize_t ret; if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING))) return -EIO; if (!iov_iter_count(iter)) return 0; if (iocb->ki_flags & IOCB_DIRECT && !(file->f_mode & FMODE_CAN_ODIRECT)) return -EINVAL; old_cred = override_creds_light(ctx->cred); if (is_sync_kiocb(iocb)) { rwf_t rwf = iocb_to_rw_flags(flags); ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf); } else { ret = -ENOMEM; aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL); if (!aio) goto out; aio->orig_iocb = iocb; kiocb_clone(&aio->iocb, iocb, get_file(file)); aio->iocb.ki_complete = backing_aio_rw_complete; refcount_set(&aio->ref, 2); ret = vfs_iocb_iter_read(file, &aio->iocb, iter); backing_aio_put(aio); if (ret != -EIOCBQUEUED) backing_aio_cleanup(aio, ret); } out: revert_creds_light(old_cred); if (ctx->accessed) ctx->accessed(iocb->ki_filp); return ret; } EXPORT_SYMBOL_GPL(backing_file_read_iter); ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter, struct kiocb *iocb, int flags, struct backing_file_ctx *ctx) { const struct cred *old_cred; ssize_t ret; if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING))) return -EIO; if (!iov_iter_count(iter)) return 0; ret = file_remove_privs(iocb->ki_filp); if (ret) return ret; if (iocb->ki_flags & IOCB_DIRECT && !(file->f_mode & FMODE_CAN_ODIRECT)) return -EINVAL; /* * Stacked filesystems don't support deferred completions, don't copy * this property in case it is set by the issuer. */ flags &= ~IOCB_DIO_CALLER_COMP; old_cred = override_creds_light(ctx->cred); if (is_sync_kiocb(iocb)) { rwf_t rwf = iocb_to_rw_flags(flags); ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf); if (ctx->end_write) ctx->end_write(iocb, ret); } else { struct backing_aio *aio; ret = backing_aio_init_wq(iocb); if (ret) goto out; ret = -ENOMEM; aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL); if (!aio) goto out; aio->orig_iocb = iocb; aio->end_write = ctx->end_write; kiocb_clone(&aio->iocb, iocb, get_file(file)); aio->iocb.ki_flags = flags; aio->iocb.ki_complete = backing_aio_queue_completion; refcount_set(&aio->ref, 2); ret = vfs_iocb_iter_write(file, &aio->iocb, iter); backing_aio_put(aio); if (ret != -EIOCBQUEUED) backing_aio_cleanup(aio, ret); } out: revert_creds_light(old_cred); return ret; } EXPORT_SYMBOL_GPL(backing_file_write_iter); ssize_t backing_file_splice_read(struct file *in, struct kiocb *iocb, struct pipe_inode_info *pipe, size_t len, unsigned int flags, struct backing_file_ctx *ctx) { const struct cred *old_cred; ssize_t ret; if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING))) return -EIO; old_cred = override_creds_light(ctx->cred); ret = vfs_splice_read(in, &iocb->ki_pos, pipe, len, flags); revert_creds_light(old_cred); if (ctx->accessed) ctx->accessed(iocb->ki_filp); return ret; } EXPORT_SYMBOL_GPL(backing_file_splice_read); ssize_t backing_file_splice_write(struct pipe_inode_info *pipe, struct file *out, struct kiocb *iocb, size_t len, unsigned int flags, struct backing_file_ctx *ctx) { const struct cred *old_cred; ssize_t ret; if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING))) return -EIO; if (!out->f_op->splice_write) return -EINVAL; ret = file_remove_privs(iocb->ki_filp); if (ret) return ret; old_cred = override_creds_light(ctx->cred); file_start_write(out); ret = out->f_op->splice_write(pipe, out, &iocb->ki_pos, len, flags); file_end_write(out); revert_creds_light(old_cred); if (ctx->end_write) ctx->end_write(iocb, ret); return ret; } EXPORT_SYMBOL_GPL(backing_file_splice_write); int backing_file_mmap(struct file *file, struct vm_area_struct *vma, struct backing_file_ctx *ctx) { const struct cred *old_cred; int ret; if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING))) return -EIO; if (!file->f_op->mmap) return -ENODEV; vma_set_file(vma, file); old_cred = override_creds_light(ctx->cred); ret = call_mmap(vma->vm_file, vma); revert_creds_light(old_cred); if (ctx->accessed) ctx->accessed(vma->vm_file); return ret; } EXPORT_SYMBOL_GPL(backing_file_mmap); static int __init backing_aio_init(void) { backing_aio_cachep = KMEM_CACHE(backing_aio, SLAB_HWCACHE_ALIGN); if (!backing_aio_cachep) return -ENOMEM; return 0; } fs_initcall(backing_aio_init);
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