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| author |   Miklos Szeredi <mszeredi@redhat.com> | 2020-05-14 16:44:23 +0200 |
|---|---|---|
| committer | Miklos Szeredi <mszeredi@redhat.com> | 2020-05-14 16:44:23 +0200 |
| commit | a3c751a50fe6bbe50eb7622a14b18b361804ee0c (patch) | |
| tree | c06d4a05f89fea5d5ea3f4729ab6748140bbb77a /fs | |
| parent | Linux 5.7-rc4 (diff) | |
| download | linux-dev-a3c751a50fe6bbe50eb7622a14b18b361804ee0c.tar.xz linux-dev-a3c751a50fe6bbe50eb7622a14b18b361804ee0c.zip | |
vfs: allow unprivileged whiteout creation
Whiteouts, unlike real device node should not require privileges to create.
The general concern with device nodes is that opening them can have side
effects. The kernel already avoids zero major (see
Documentation/admin-guide/devices.txt). To be on the safe side the patch
explicitly forbids registering a char device with 0/0 number (see
cdev_add()).
This guarantees that a non-O_PATH open on a whiteout will fail with ENODEV;
i.e. it won't have any side effect.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/char_dev.c | 3 | ||||
| -rw-r--r-- | fs/namei.c | 21 |
2 files changed, 6 insertions, 18 deletions
diff --git a/fs/char_dev.c b/fs/char_dev.c index c5e6eff5a381..ba0ded7842a7 100644 --- a/fs/char_dev.c +++ b/fs/char_dev.c @@ -483,6 +483,9 @@ int cdev_add(struct cdev *p, dev_t dev, unsigned count) p->dev = dev; p->count = count; + if (WARN_ON(dev == WHITEOUT_DEV)) + return -EBUSY; + error = kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p); if (error) diff --git a/fs/namei.c b/fs/namei.c index a320371899cf..d81f73ff1a8b 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3505,12 +3505,14 @@ EXPORT_SYMBOL(user_path_create); int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev) { + bool is_whiteout = S_ISCHR(mode) && dev == WHITEOUT_DEV; int error = may_create(dir, dentry); if (error) return error; - if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD)) + if ((S_ISCHR(mode) || S_ISBLK(mode)) && !is_whiteout && + !capable(CAP_MKNOD)) return -EPERM; if (!dir->i_op->mknod) @@ -4345,9 +4347,6 @@ static int do_renameat2(int olddfd, const char __user *oldname, int newdfd, (flags & RENAME_EXCHANGE)) return -EINVAL; - if ((flags & RENAME_WHITEOUT) && !capable(CAP_MKNOD)) - return -EPERM; - if (flags & RENAME_EXCHANGE) target_flags = 0; @@ -4483,20 +4482,6 @@ SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newna return do_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0); } -int vfs_whiteout(struct inode *dir, struct dentry *dentry) -{ - int error = may_create(dir, dentry); - if (error) - return error; - - if (!dir->i_op->mknod) - return -EPERM; - - return dir->i_op->mknod(dir, dentry, - S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV); -} -EXPORT_SYMBOL(vfs_whiteout); - int readlink_copy(char __user *buffer, int buflen, const char *link) { int len = PTR_ERR(link); |