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 <gorcunov@openvz.org>
Acked-by: Andrey Vagin <avagin@openvz.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 322904c3ebdf990c951e08ef3166dca321d43ae0..e7e9901c37907602e5391771efc8eb4ce6e4bde7 100644 (file)
--- 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 6daf6d4971f65266c3c83e684af231dbafc452c0..d8625d214ea7a4b02a90f1d70b99b389b5810a8c 100644 (file)
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -14,6 +14,7 @@
 #define _LINUX_EVENTPOLL_H
 
 #include <uapi/linux/eventpoll.h>
+#include <uapi/linux/kcmp.h>
 
 
 /* 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 84df14b373601486bdc2b684c49a2ae8b25e3147..481e103da78ed42a5a76447e836ee8374541d7c7 100644 (file)
--- 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 <linux/types.h>
+
 /* 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 3a47fa998fe07277c592f62de36f59dad0d09f8b..ea34ed8bb9529c7b7a2a38b0a4e050995b4ba97e 100644 (file)
--- a/kernel/kcmp.c
+++ b/kernel/kcmp.c
@@ -11,6 +11,10 @@
 #include <linux/bug.h>
 #include <linux/err.h>
 #include <linux/kcmp.h>
+#include <linux/capability.h>
+#include <linux/list.h>
+#include <linux/eventpoll.h>
+#include <linux/file.h>
 
 #include <asm/unistd.h>
 
@@ -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;