9c225f2655
Our write() system call has always been atomic in the sense that you get the expected thread-safe contiguous write, but we haven't actually guaranteed that concurrent writes are serialized wrt f_pos accesses, so threads (or processes) that share a file descriptor and use "write()" concurrently would quite likely overwrite each others data. This violates POSIX.1-2008/SUSv4 Section XSI 2.9.7 that says: "2.9.7 Thread Interactions with Regular File Operations All of the following functions shall be atomic with respect to each other in the effects specified in POSIX.1-2008 when they operate on regular files or symbolic links: [...]" and one of the effects is the file position update. This unprotected file position behavior is not new behavior, and nobody has ever cared. Until now. Yongzhi Pan reported unexpected behavior to Michael Kerrisk that was due to this. This resolves the issue with a f_pos-specific lock that is taken by read/write/lseek on file descriptors that may be shared across threads or processes. Reported-by: Yongzhi Pan <panyongzhi@gmail.com> Reported-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
76 lines
1.8 KiB
C
76 lines
1.8 KiB
C
/*
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* Wrapper functions for accessing the file_struct fd array.
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*/
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#ifndef __LINUX_FILE_H
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#define __LINUX_FILE_H
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#include <linux/compiler.h>
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#include <linux/types.h>
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#include <linux/posix_types.h>
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struct file;
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extern void fput(struct file *);
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struct file_operations;
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struct vfsmount;
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struct dentry;
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struct path;
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extern struct file *alloc_file(struct path *, fmode_t mode,
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const struct file_operations *fop);
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static inline void fput_light(struct file *file, int fput_needed)
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{
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if (fput_needed)
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fput(file);
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}
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struct fd {
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struct file *file;
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unsigned int flags;
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};
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#define FDPUT_FPUT 1
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#define FDPUT_POS_UNLOCK 2
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static inline void fdput(struct fd fd)
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{
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if (fd.flags & FDPUT_FPUT)
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fput(fd.file);
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}
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extern struct file *fget(unsigned int fd);
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extern struct file *fget_light(unsigned int fd, int *fput_needed);
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static inline struct fd fdget(unsigned int fd)
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{
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int b;
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struct file *f = fget_light(fd, &b);
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return (struct fd){f,b};
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}
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extern struct file *fget_raw(unsigned int fd);
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extern struct file *fget_raw_light(unsigned int fd, int *fput_needed);
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static inline struct fd fdget_raw(unsigned int fd)
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{
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int b;
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struct file *f = fget_raw_light(fd, &b);
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return (struct fd){f,b};
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}
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extern int f_dupfd(unsigned int from, struct file *file, unsigned flags);
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extern int replace_fd(unsigned fd, struct file *file, unsigned flags);
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extern void set_close_on_exec(unsigned int fd, int flag);
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extern bool get_close_on_exec(unsigned int fd);
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extern void put_filp(struct file *);
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extern int get_unused_fd_flags(unsigned flags);
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#define get_unused_fd() get_unused_fd_flags(0)
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extern void put_unused_fd(unsigned int fd);
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extern void fd_install(unsigned int fd, struct file *file);
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extern void flush_delayed_fput(void);
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extern void __fput_sync(struct file *);
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#endif /* __LINUX_FILE_H */
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