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authorDavid Howells <dhowells@redhat.com>2018-11-01 23:36:23 +0000
committerAl Viro <viro@zeniv.linux.org.uk>2019-03-20 18:49:06 -0400
commitcf3cba4a429be43e5527a3f78859b1bfd9ebc5fb (patch)
tree41f4c4a999e7e22644b0f3a220208519dc1f4ccd
parent93766fbd2696c2c4453dd8e1070977e9cd4e6b6d (diff)
vfs: syscall: Add fspick() to select a superblock for reconfiguration
Provide an fspick() system call that can be used to pick an existing mountpoint into an fs_context which can thereafter be used to reconfigure a superblock (equivalent of the superblock side of -o remount). This looks like: int fd = fspick(AT_FDCWD, "/mnt", FSPICK_CLOEXEC | FSPICK_NO_AUTOMOUNT); fsconfig(fd, FSCONFIG_SET_FLAG, "intr", NULL, 0); fsconfig(fd, FSCONFIG_SET_FLAG, "noac", NULL, 0); fsconfig(fd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0); At the point of fspick being called, the file descriptor referring to the filesystem context is in exactly the same state as the one that was created by fsopen() after fsmount() has been successfully called. Signed-off-by: David Howells <dhowells@redhat.com> cc: linux-api@vger.kernel.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--arch/x86/entry/syscalls/syscall_32.tbl2
-rw-r--r--arch/x86/entry/syscalls/syscall_64.tbl1
-rw-r--r--fs/fsopen.c57
-rw-r--r--include/linux/syscalls.h1
-rw-r--r--include/uapi/linux/mount.h8
5 files changed, 68 insertions, 1 deletions
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 5b5c9189c507..4cd5f982b1e5 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -403,7 +403,7 @@
389 i386 fsopen sys_fsopen __ia32_sys_fsopen
390 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig
391 i386 fsmount sys_fsmount __ia32_sys_fsmount
-# don't use number 392, add new calls at the end
+392 i386 fspick sys_fspick __ia32_sys_fspick
393 i386 semget sys_semget __ia32_sys_semget
394 i386 semctl sys_semctl __ia32_compat_sys_semctl
395 i386 shmget sys_shmget __ia32_sys_shmget
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 984ad594bb2b..64ca0d06259a 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -348,6 +348,7 @@
337 common fsopen __x64_sys_fsopen
338 common fsconfig __x64_sys_fsconfig
339 common fsmount __x64_sys_fsmount
+340 common fspick __x64_sys_fspick
# don't use numbers 387 through 423, add new calls after the last
# 'common' entry
424 common pidfd_send_signal __x64_sys_pidfd_send_signal
diff --git a/fs/fsopen.c b/fs/fsopen.c
index 65cc2f68f994..3bb9c0c8cbcc 100644
--- a/fs/fsopen.c
+++ b/fs/fsopen.c
@@ -157,6 +157,63 @@ err_fc:
}
/*
+ * Pick a superblock into a context for reconfiguration.
+ */
+SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags)
+{
+ struct fs_context *fc;
+ struct path target;
+ unsigned int lookup_flags;
+ int ret;
+
+ if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if ((flags & ~(FSPICK_CLOEXEC |
+ FSPICK_SYMLINK_NOFOLLOW |
+ FSPICK_NO_AUTOMOUNT |
+ FSPICK_EMPTY_PATH)) != 0)
+ return -EINVAL;
+
+ lookup_flags = LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+ if (flags & FSPICK_SYMLINK_NOFOLLOW)
+ lookup_flags &= ~LOOKUP_FOLLOW;
+ if (flags & FSPICK_NO_AUTOMOUNT)
+ lookup_flags &= ~LOOKUP_AUTOMOUNT;
+ if (flags & FSPICK_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+ ret = user_path_at(dfd, path, lookup_flags, &target);
+ if (ret < 0)
+ goto err;
+
+ ret = -EINVAL;
+ if (target.mnt->mnt_root != target.dentry)
+ goto err_path;
+
+ fc = fs_context_for_reconfigure(target.dentry, 0, 0);
+ if (IS_ERR(fc)) {
+ ret = PTR_ERR(fc);
+ goto err_path;
+ }
+
+ fc->phase = FS_CONTEXT_RECONF_PARAMS;
+
+ ret = fscontext_alloc_log(fc);
+ if (ret < 0)
+ goto err_fc;
+
+ path_put(&target);
+ return fscontext_create_fd(fc, flags & FSPICK_CLOEXEC ? O_CLOEXEC : 0);
+
+err_fc:
+ put_fs_context(fc);
+err_path:
+ path_put(&target);
+err:
+ return ret;
+}
+
+/*
* Check the state and apply the configuration. Note that this function is
* allowed to 'steal' the value by setting param->xxx to NULL before returning.
*/
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 0e697f595278..e2870fe1be5b 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -993,6 +993,7 @@ asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags);
asmlinkage long sys_fsconfig(int fs_fd, unsigned int cmd, const char __user *key,
const void __user *value, int aux);
asmlinkage long sys_fsmount(int fs_fd, unsigned int flags, unsigned int ms_flags);
+asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags);
asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
siginfo_t __user *info,
unsigned int flags);
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 3888d3b91dc5..96a0240f23fe 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -78,6 +78,14 @@
#define FSOPEN_CLOEXEC 0x00000001
/*
+ * fspick() flags.
+ */
+#define FSPICK_CLOEXEC 0x00000001
+#define FSPICK_SYMLINK_NOFOLLOW 0x00000002
+#define FSPICK_NO_AUTOMOUNT 0x00000004
+#define FSPICK_EMPTY_PATH 0x00000008
+
+/*
* The type of fsconfig() call made.
*/
enum fsconfig_command {