eef99860c6
commit 1e7107c5ef44431bc1ebbd4c353f1d7c22e5f2ec upstream. Richard reported sporadic (roughly one in 10 or so) null dereferences and other strange behaviour for a set of automated LTP tests. Things like: BUG: kernel NULL pointer dereference, address: 0000000000000008 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 0 PID: 1516 Comm: umount Not tainted 5.10.0-yocto-standard #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014 RIP: 0010:kernfs_sop_show_path+0x1b/0x60 ...or these others: RIP: 0010:do_mkdirat+0x6a/0xf0 RIP: 0010:d_alloc_parallel+0x98/0x510 RIP: 0010:do_readlinkat+0x86/0x120 There were other less common instances of some kind of a general scribble but the common theme was mount and cgroup and a dubious dentry triggering the NULL dereference. I was only able to reproduce it under qemu by replicating Richard's setup as closely as possible - I never did get it to happen on bare metal, even while keeping everything else the same. In commit71d883c37e("cgroup_do_mount(): massage calling conventions") we see this as a part of the overall change: -------------- struct cgroup_subsys *ss; - struct dentry *dentry; [...] - dentry = cgroup_do_mount(&cgroup_fs_type, fc->sb_flags, root, - CGROUP_SUPER_MAGIC, ns); [...] - if (percpu_ref_is_dying(&root->cgrp.self.refcnt)) { - struct super_block *sb = dentry->d_sb; - dput(dentry); + ret = cgroup_do_mount(fc, CGROUP_SUPER_MAGIC, ns); + if (!ret && percpu_ref_is_dying(&root->cgrp.self.refcnt)) { + struct super_block *sb = fc->root->d_sb; + dput(fc->root); deactivate_locked_super(sb); msleep(10); return restart_syscall(); } -------------- In changing from the local "*dentry" variable to using fc->root, we now export/leave that dentry pointer in the file context after doing the dput() in the unlikely "is_dying" case. With LTP doing a crazy amount of back to back mount/unmount [testcases/bin/cgroup_regression_5_1.sh] the unlikely becomes slightly likely and then bad things happen. A fix would be to not leave the stale reference in fc->root as follows: -------------- dput(fc->root); + fc->root = NULL; deactivate_locked_super(sb); -------------- ...but then we are just open-coding a duplicate of fc_drop_locked() so we simply use that instead. Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Tejun Heo <tj@kernel.org> Cc: Zefan Li <lizefan.x@bytedance.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: stable@vger.kernel.org # v5.1+ Reported-by: Richard Purdie <richard.purdie@linuxfoundation.org> Fixes:71d883c37e("cgroup_do_mount(): massage calling conventions") Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
191 lines
5.0 KiB
C
191 lines
5.0 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/* fs/ internal definitions
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*
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* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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struct super_block;
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struct file_system_type;
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struct iomap;
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struct iomap_ops;
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struct linux_binprm;
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struct path;
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struct mount;
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struct shrink_control;
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struct fs_context;
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struct user_namespace;
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/*
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* block_dev.c
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*/
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#ifdef CONFIG_BLOCK
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extern void __init bdev_cache_init(void);
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extern int __sync_blockdev(struct block_device *bdev, int wait);
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#else
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static inline void bdev_cache_init(void)
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{
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}
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static inline int __sync_blockdev(struct block_device *bdev, int wait)
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{
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return 0;
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}
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#endif
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/*
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* buffer.c
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*/
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extern void guard_bio_eod(struct bio *bio);
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extern int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
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get_block_t *get_block, struct iomap *iomap);
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/*
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* char_dev.c
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*/
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extern void __init chrdev_init(void);
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/*
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* fs_context.c
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*/
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extern const struct fs_context_operations legacy_fs_context_ops;
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extern int parse_monolithic_mount_data(struct fs_context *, void *);
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extern void vfs_clean_context(struct fs_context *fc);
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extern int finish_clean_context(struct fs_context *fc);
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/*
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* namei.c
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*/
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extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
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struct path *path, struct path *root);
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extern int user_path_mountpoint_at(int, const char __user *, unsigned int, struct path *);
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extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
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const char *, unsigned int, struct path *);
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long do_mknodat(int dfd, const char __user *filename, umode_t mode,
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unsigned int dev);
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long do_mkdirat(int dfd, const char __user *pathname, umode_t mode);
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long do_rmdir(int dfd, const char __user *pathname);
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long do_unlinkat(int dfd, struct filename *name);
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long do_symlinkat(const char __user *oldname, int newdfd,
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const char __user *newname);
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int do_linkat(int olddfd, const char __user *oldname, int newdfd,
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const char __user *newname, int flags);
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/*
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* namespace.c
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*/
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extern void *copy_mount_options(const void __user *);
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extern char *copy_mount_string(const void __user *);
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extern struct vfsmount *lookup_mnt(const struct path *);
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extern int finish_automount(struct vfsmount *, struct path *);
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extern int sb_prepare_remount_readonly(struct super_block *);
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extern void __init mnt_init(void);
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extern int __mnt_want_write_file(struct file *);
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extern void __mnt_drop_write_file(struct file *);
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extern void dissolve_on_fput(struct vfsmount *);
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/*
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* fs_struct.c
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*/
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extern void chroot_fs_refs(const struct path *, const struct path *);
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/*
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* file_table.c
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*/
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extern struct file *alloc_empty_file(int, const struct cred *);
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extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
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/*
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* super.c
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*/
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extern int reconfigure_super(struct fs_context *);
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extern bool trylock_super(struct super_block *sb);
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extern struct super_block *user_get_super(dev_t);
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extern bool mount_capable(struct fs_context *);
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/*
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* open.c
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*/
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struct open_flags {
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int open_flag;
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umode_t mode;
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int acc_mode;
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int intent;
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int lookup_flags;
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};
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extern struct file *do_filp_open(int dfd, struct filename *pathname,
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const struct open_flags *op);
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extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
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const char *, const struct open_flags *);
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long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
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long do_faccessat(int dfd, const char __user *filename, int mode);
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int do_fchmodat(int dfd, const char __user *filename, umode_t mode);
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int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
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int flag);
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extern int vfs_open(const struct path *, struct file *);
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/*
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* inode.c
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*/
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extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
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extern void inode_add_lru(struct inode *inode);
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extern int dentry_needs_remove_privs(struct dentry *dentry);
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/*
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* fs-writeback.c
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*/
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extern void inode_io_list_del(struct inode *inode);
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extern long get_nr_dirty_inodes(void);
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extern int invalidate_inodes(struct super_block *, bool);
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/*
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* dcache.c
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*/
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extern struct dentry *__d_alloc(struct super_block *, const struct qstr *);
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extern int d_set_mounted(struct dentry *dentry);
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extern long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc);
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extern struct dentry *d_alloc_cursor(struct dentry *);
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extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
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extern char *simple_dname(struct dentry *, char *, int);
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extern void dput_to_list(struct dentry *, struct list_head *);
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extern void shrink_dentry_list(struct list_head *);
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/*
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* read_write.c
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*/
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extern int rw_verify_area(int, struct file *, const loff_t *, size_t);
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/*
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* pipe.c
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*/
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extern const struct file_operations pipefifo_fops;
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/*
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* fs_pin.c
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*/
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extern void group_pin_kill(struct hlist_head *p);
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extern void mnt_pin_kill(struct mount *m);
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/*
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* fs/nsfs.c
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*/
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extern const struct dentry_operations ns_dentry_operations;
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/*
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* fs/ioctl.c
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*/
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extern int do_vfs_ioctl(struct file *file, unsigned int fd, unsigned int cmd,
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unsigned long arg);
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/* direct-io.c: */
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int sb_init_dio_done_wq(struct super_block *sb);
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