Messages in this thread |  | | Date | Mon, 16 Dec 2019 02:36:48 +0100 | From | Ondřej Jirman <> | Subject | Re: [PATCH 3/3] init: use do_mount() instead of ksys_mount() |
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On Mon, Dec 16, 2019 at 02:35:36AM +0100, megi xff wrote: > 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):
5.5-rc2 of course. :)
> 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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