Messages in this thread Patch in this message |  | | Date | Mon, 16 Dec 2019 02:35:36 +0100 | From | Ondřej Jirman <> | Subject | Re: [PATCH 3/3] init: use do_mount() instead of ksys_mount() |
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Hello,
On Thu, Dec 12, 2019 at 02:57:24PM +0100, Dominik Brodowski wrote: > In prepare_namespace(), do_mount() can be used instead of ksys_mount() > as the first and third argument are const strings in the kernel, the > second and fourth argument are passed through anyway, and the fifth > argument is NULL. > > In do_mount_root(), ksys_mount() is called with the first and third > argument being already kernelspace strings, which do not need to be > copied over from userspace to kernelspace (again). The second and > fourth arguments are passed through to do_mount() anyway. The fifth > argument, while already residing in kernelspace, needs to be put into > a page of its own. Then, do_mount() can be used instead of > ksys_mount(). > > Once this is done, there are no in-kernel users to ksys_mount() left, > which can therefore be removed. > > Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net> > --- > fs/namespace.c | 10 ++-------- > include/linux/syscalls.h | 2 -- > init/do_mounts.c | 28 ++++++++++++++++++++++------ > 3 files changed, 24 insertions(+), 16 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 2fd0c8bcb8c1..be601d3a8008 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -3325,8 +3325,8 @@ struct dentry *mount_subtree(struct vfsmount *m, const char *name) > } > EXPORT_SYMBOL(mount_subtree); > > -int ksys_mount(const char __user *dev_name, const char __user *dir_name, > - const char __user *type, unsigned long flags, void __user *data) > +SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name, > + char __user *, type, unsigned long, flags, void __user *, data) > { > int ret; > char *kernel_type; > @@ -3359,12 +3359,6 @@ int ksys_mount(const char __user *dev_name, const char __user *dir_name, > return ret; > } > > -SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name, > - char __user *, type, unsigned long, flags, void __user *, data) > -{ > - return ksys_mount(dev_name, dir_name, type, flags, data); > -} > - > /* > * Create a kernel mount representation for a new, prepared superblock > * (specified by fs_fd) and attach to an open_tree-like file descriptor. > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h > index d0391cc2dae9..5262b7a76d39 100644 > --- a/include/linux/syscalls.h > +++ b/include/linux/syscalls.h > @@ -1231,8 +1231,6 @@ asmlinkage long sys_ni_syscall(void); > * the ksys_xyzyyz() functions prototyped below. > */ > > -int ksys_mount(const char __user *dev_name, const char __user *dir_name, > - const char __user *type, unsigned long flags, void __user *data); > int ksys_umount(char __user *name, int flags); > int ksys_dup(unsigned int fildes); > int ksys_chroot(const char __user *filename); > diff --git a/init/do_mounts.c b/init/do_mounts.c > index 43f6d098c880..f55cbd9cb818 100644 > --- a/init/do_mounts.c > +++ b/init/do_mounts.c > @@ -387,12 +387,25 @@ static void __init get_fs_names(char *page) > *s = '\0'; > } > > -static int __init do_mount_root(char *name, char *fs, int flags, void *data) > +static int __init do_mount_root(const char *name, const char *fs, > + const int flags, const void *data) > { > struct super_block *s; > - int err = ksys_mount(name, "/root", fs, flags, data); > - if (err) > - return err; > + char *data_page; > + struct page *p; > + int ret; > + > + /* do_mount() requires a full page as fifth argument */ > + p = alloc_page(GFP_KERNEL); > + if (!p) > + return -ENOMEM; > + > + data_page = page_address(p); > + strncpy(data_page, data, PAGE_SIZE - 1);
I tried 5.2-rc2 and I get kernel OOPS/panic here (do_mount_root gets inlined into mount_block_root):
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Mem abort info: ESR = 0x96000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000005 CM = 0, WnR = 0 [0000000000000000] user address but active_mm is swapper Internal error: Oops: 96000005 [#1] SMP Modules linked in: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc2-00128-ge93c94cc04ae #5 Hardware name: OrangePi 3 (DT) pstate: 80000005 (Nzcv daif -PAN -UAO) pc : strncpy+0x10/0x30 lr : do_mount_root+0x70/0x114 sp : ffffffc01002bd20 x29: ffffffc01002bd20 x28: 0000000000000000 x27: 0000000000000000 x26: ffffffc011400468 x25: ffffffc0110d23a0 x24: ffffffff01c396c0 x23: 0000000000008000 x22: ffffff8078e5b000 x21: ffffffc0110d23a0 x20: ffffffc0110d2220 x19: ffffffff01c39700 x18: 00000000fffffffe x17: 00000000dbaba8be x16: 0000000000000000 x15: ffffffffffffffff x14: ffffff0000000000 x13: ffffff807b490000 x12: 0000000000000000 x11: 0000000000000000 x10: ffffff807bb96120 x9 : 0000000000000000 x8 : 0000000000000000 x7 : ffffffc06a6e6000 x6 : 0000000000000000 x5 : 000000000003b820 x4 : ffffff8078e5cfff x3 : 0000000000000201 x2 : ffffff8078e5c000 x1 : 0000000000000000 x0 : ffffff8078e5c000 Call trace: strncpy+0x10/0x30 mount_block_root+0x100/0x224 mount_root+0x10c/0x124 prepare_namespace+0x12c/0x168 kernel_init_freeable+0x214/0x258 kernel_init+0x10/0xfc ret_from_fork+0x10/0x1c Code: b4000142 8b020004 aa0003e2 d503201f (39400023) ---[ end trace b72d58d1ea940426 ]--- Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b SMP: stopping secondary CPUs Kernel Offset: disabled CPU features: 0x00002,20002000 Memory Limit: none Rebooting in 3 seconds..
regards, o.
> + ret = do_mount(name, "/root", fs, flags, data_page); > + if (ret) > + goto out; > > ksys_chdir("/root"); > s = current->fs->pwd.dentry->d_sb; > @@ -402,7 +415,10 @@ static int __init do_mount_root(char *name, char *fs, int flags, void *data) > s->s_type->name, > sb_rdonly(s) ? " readonly" : "", > MAJOR(ROOT_DEV), MINOR(ROOT_DEV)); > - return 0; > + > +out: > + put_page(p); > + return ret; > } > > void __init mount_block_root(char *name, int flags) > @@ -671,7 +687,7 @@ void __init prepare_namespace(void) > mount_root(); > out: > devtmpfs_mount(); > - ksys_mount(".", "/", NULL, MS_MOVE, NULL); > + do_mount(".", "/", NULL, MS_MOVE, NULL); > ksys_chroot("."); > } > > -- > 2.24.1 >
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