From 0791e3644e5ef21646fe565b9061788d05ec71d4 Mon Sep 17 00:00:00 2001 From: Cyrill Gorcunov Date: Wed, 12 Jul 2017 14:34:28 -0700 Subject: [PATCH] kcmp: add KCMP_EPOLL_TFD mode to compare epoll target files With current epoll architecture target files are addressed with file_struct and file descriptor number, where the last is not unique. Moreover files can be transferred from another process via unix socket, added into queue and closed then so we won't find this descriptor in the task fdinfo list. Thus to checkpoint and restore such processes CRIU needs to find out where exactly the target file is present to add it into epoll queue. For this sake one can use kcmp call where some particular target file from the queue is compared with arbitrary file passed as an argument. Because epoll target files can have same file descriptor number but different file_struct a caller should explicitly specify the offset within. To test if some particular file is matching entry inside epoll one have to - fill kcmp_epoll_slot structure with epoll file descriptor, target file number and target file offset (in case if only one target is present then it should be 0) - call kcmp as kcmp(pid1, pid2, KCMP_EPOLL_TFD, fd, &kcmp_epoll_slot) - the kernel fetch file pointer matching file descriptor @fd of pid1 - lookups for file struct in epoll queue of pid2 and returns traditional 0,1,2 result for sorting purpose Link: http://lkml.kernel.org/r/20170424154423.511592110@gmail.com Signed-off-by: Cyrill Gorcunov Acked-by: Andrey Vagin Cc: Al Viro Cc: Pavel Emelyanov Cc: Michael Kerrisk Cc: Jason Baron Cc: Andy Lutomirski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/eventpoll.c | 42 +++++++++++++++++++++++++++++ include/linux/eventpoll.h | 3 +++ include/uapi/linux/kcmp.h | 10 +++++++ kernel/kcmp.c | 57 +++++++++++++++++++++++++++++++++++++++ 4 files changed, 112 insertions(+) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 322904c3ebdf..e7e9901c3790 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1077,6 +1077,48 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) return epir; } +static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff) +{ + struct rb_node *rbp; + struct epitem *epi; + + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (epi->ffd.fd == tfd) { + if (toff == 0) + return epi; + else + toff--; + } + cond_resched(); + } + + return NULL; +} + +struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, + unsigned long toff) +{ + struct file *file_raw; + struct eventpoll *ep; + struct epitem *epi; + + if (!is_file_epoll(file)) + return ERR_PTR(-EINVAL); + + ep = file->private_data; + + mutex_lock(&ep->mtx); + epi = ep_find_tfd(ep, tfd, toff); + if (epi) + file_raw = epi->ffd.file; + else + file_raw = ERR_PTR(-ENOENT); + mutex_unlock(&ep->mtx); + + return file_raw; +} + /* * This is the callback that is passed to the wait queue wakeup * mechanism. It is called by the stored file descriptors when they diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h index 6daf6d4971f6..d8625d214ea7 100644 --- a/include/linux/eventpoll.h +++ b/include/linux/eventpoll.h @@ -14,6 +14,7 @@ #define _LINUX_EVENTPOLL_H #include +#include /* Forward declarations to avoid compiler errors */ @@ -22,6 +23,8 @@ struct file; #ifdef CONFIG_EPOLL +struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long toff); + /* Used to initialize the epoll bits inside the "struct file" */ static inline void eventpoll_init_file(struct file *file) { diff --git a/include/uapi/linux/kcmp.h b/include/uapi/linux/kcmp.h index 84df14b37360..481e103da78e 100644 --- a/include/uapi/linux/kcmp.h +++ b/include/uapi/linux/kcmp.h @@ -1,6 +1,8 @@ #ifndef _UAPI_LINUX_KCMP_H #define _UAPI_LINUX_KCMP_H +#include + /* Comparison type */ enum kcmp_type { KCMP_FILE, @@ -10,8 +12,16 @@ enum kcmp_type { KCMP_SIGHAND, KCMP_IO, KCMP_SYSVSEM, + KCMP_EPOLL_TFD, KCMP_TYPES, }; +/* Slot for KCMP_EPOLL_TFD */ +struct kcmp_epoll_slot { + __u32 efd; /* epoll file descriptor */ + __u32 tfd; /* target file number */ + __u32 toff; /* target offset within same numbered sequence */ +}; + #endif /* _UAPI_LINUX_KCMP_H */ diff --git a/kernel/kcmp.c b/kernel/kcmp.c index 3a47fa998fe0..ea34ed8bb952 100644 --- a/kernel/kcmp.c +++ b/kernel/kcmp.c @@ -11,6 +11,10 @@ #include #include #include +#include +#include +#include +#include #include @@ -94,6 +98,56 @@ static int kcmp_lock(struct mutex *m1, struct mutex *m2) return err; } +#ifdef CONFIG_EPOLL +static int kcmp_epoll_target(struct task_struct *task1, + struct task_struct *task2, + unsigned long idx1, + struct kcmp_epoll_slot __user *uslot) +{ + struct file *filp, *filp_epoll, *filp_tgt; + struct kcmp_epoll_slot slot; + struct files_struct *files; + + if (copy_from_user(&slot, uslot, sizeof(slot))) + return -EFAULT; + + filp = get_file_raw_ptr(task1, idx1); + if (!filp) + return -EBADF; + + files = get_files_struct(task2); + if (!files) + return -EBADF; + + spin_lock(&files->file_lock); + filp_epoll = fcheck_files(files, slot.efd); + if (filp_epoll) + get_file(filp_epoll); + else + filp_tgt = ERR_PTR(-EBADF); + spin_unlock(&files->file_lock); + put_files_struct(files); + + if (filp_epoll) { + filp_tgt = get_epoll_tfile_raw_ptr(filp_epoll, slot.tfd, slot.toff); + fput(filp_epoll); + } else + + if (IS_ERR(filp_tgt)) + return PTR_ERR(filp_tgt); + + return kcmp_ptr(filp, filp_tgt, KCMP_FILE); +} +#else +static int kcmp_epoll_target(struct task_struct *task1, + struct task_struct *task2, + unsigned long idx1, + struct kcmp_epoll_slot __user *uslot) +{ + return -EOPNOTSUPP; +} +#endif + SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, unsigned long, idx1, unsigned long, idx2) { @@ -165,6 +219,9 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, ret = -EOPNOTSUPP; #endif break; + case KCMP_EPOLL_TFD: + ret = kcmp_epoll_target(task1, task2, idx1, (void *)idx2); + break; default: ret = -EINVAL; break; -- 2.30.2