Messages in this thread | | | Subject | Re: [PATCH 31/34] vfs: syscall: Add fspick() to select a superblock for reconfiguration [ver #12] | From | Alan Jenkins <> | Date | Fri, 12 Oct 2018 15:49:50 +0100 |
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On 21/09/2018 17:34, David Howells wrote: > 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 > --- > > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > fs/fsopen.c | 54 ++++++++++++++++++++++++++++++++ > include/linux/syscalls.h | 1 + > include/uapi/linux/fs.h | 5 +++ > 5 files changed, 62 insertions(+) > > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl > index c78b68256f8a..d1eb6c815790 100644 > --- a/arch/x86/entry/syscalls/syscall_32.tbl > +++ b/arch/x86/entry/syscalls/syscall_32.tbl > @@ -403,3 +403,4 @@ > 389 i386 fsopen sys_fsopen __ia32_sys_fsopen > 390 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig > 391 i386 fsmount sys_fsmount __ia32_sys_fsmount > +392 i386 fspick sys_fspick __ia32_sys_fspick > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl > index d44ead5d4368..d3ab703c02bb 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 > > # > # x32-specific system call numbers start at 512 to avoid cache impact > diff --git a/fs/fsopen.c b/fs/fsopen.c > index 5955a6b65596..9ead9220e2cb 100644 > --- a/fs/fsopen.c > +++ b/fs/fsopen.c > @@ -155,6 +155,60 @@ SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags) > return ret; > } > > +/* > + * 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;
This seems to accept basically any mount. Specifically: are you sure it's OK to return a handle to a SB_NO_USER superblock?
# strace -f -v -e trace=154 \ ./fspick 3</proc/self/ns/mnt 3 \ stat -f /dev/fd/3
syscall_0x154(0x3, 0x4009a1, 0x8, ...) = 0x4 File: "/dev/fd/3" ID: 0 Namelen: 255 Type: anon-inode FS Block size: 4096 Fundamental block size: 4096 Blocks: Total: 0 Free: 0 Available: 0 Inodes: Total: 0 Free: 0 +++ exited with 0 +++
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