From 2d22bb871a15bf199517b01384f6cdc85d787f1b Mon Sep 17 00:00:00 2001 From: Thomas Lamprecht Date: Thu, 3 Dec 2020 13:34:57 +0100 Subject: [PATCH] cherry-pick "vfs: allow unprivileged whiteout creation" This was in v5.7 and is rather straight forward, fixes issue for some users: https://forum.proxmox.com/threads/task-error-unable-to-restore-ct-106.79901/#post-354223 Signed-off-by: Thomas Lamprecht --- ...allow-unprivileged-whiteout-creation.patch | 122 ++++++++++++++++++ 1 file changed, 122 insertions(+) create mode 100644 patches/kernel/0008-vfs-allow-unprivileged-whiteout-creation.patch diff --git a/patches/kernel/0008-vfs-allow-unprivileged-whiteout-creation.patch b/patches/kernel/0008-vfs-allow-unprivileged-whiteout-creation.patch new file mode 100644 index 0000000..0cb12ba --- /dev/null +++ b/patches/kernel/0008-vfs-allow-unprivileged-whiteout-creation.patch @@ -0,0 +1,122 @@ +From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 +From: Miklos Szeredi +Date: Thu, 14 May 2020 16:44:23 +0200 +Subject: [PATCH] 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 +(cherry picked from commit a3c751a50fe6bbe50eb7622a14b18b361804ee0c) +Signed-off-by: Thomas Lamprecht +--- + fs/char_dev.c | 3 +++ + fs/namei.c | 21 +++------------------ + include/linux/device_cgroup.h | 3 +++ + include/linux/fs.h | 6 +++++- + 4 files changed, 14 insertions(+), 19 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 311da290a58d..4d46e093c4ea 100644 +--- a/fs/namei.c ++++ b/fs/namei.c +@@ -3690,12 +3690,14 @@ 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) +@@ -4530,9 +4532,6 @@ 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; + +@@ -4668,20 +4667,6 @@ 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); +diff --git a/include/linux/device_cgroup.h b/include/linux/device_cgroup.h +index 8557efe096dc..fc989487c273 100644 +--- a/include/linux/device_cgroup.h ++++ b/include/linux/device_cgroup.h +@@ -62,6 +62,9 @@ static inline int devcgroup_inode_mknod(int mode, dev_t dev) + if (!S_ISBLK(mode) && !S_ISCHR(mode)) + return 0; + ++ if (S_ISCHR(mode) && dev == WHITEOUT_DEV) ++ return 0; ++ + if (S_ISBLK(mode)) + type = DEVCG_DEV_BLOCK; + else +diff --git a/include/linux/fs.h b/include/linux/fs.h +index 21f93dfaf9d0..ae31b55fb69c 100644 +--- a/include/linux/fs.h ++++ b/include/linux/fs.h +@@ -1719,7 +1719,11 @@ extern int vfs_link(struct dentry *, struct inode *, struct dentry *, struct ino + extern int vfs_rmdir(struct inode *, struct dentry *); + extern int vfs_unlink(struct inode *, struct dentry *, struct inode **); + extern int vfs_rename(struct inode *, struct dentry *, struct inode *, struct dentry *, struct inode **, unsigned int); +-extern int vfs_whiteout(struct inode *, struct dentry *); ++ ++static inline int vfs_whiteout(struct inode *dir, struct dentry *dentry) ++{ ++ return vfs_mknod(dir, dentry, S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV); ++} + + extern struct dentry *vfs_tmpfile(struct dentry *dentry, umode_t mode, + int open_flag);