From 3fe6e52f062643676eb4518d68cee3bc1272091b Mon Sep 17 00:00:00 2001 From: Antonio Murdaca Date: Thu, 7 Apr 2016 15:48:25 +0200 Subject: [PATCH 1/3] ovl: override creds with the ones from the superblock mounter In user namespace the whiteout creation fails with -EPERM because the current process isn't capable(CAP_SYS_ADMIN) when setting xattr. A simple reproducer: $ mkdir upper lower work merged lower/dir $ sudo mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merged $ unshare -m -p -f -U -r bash Now as root in the user namespace: \# touch merged/dir/{1,2,3} # this will force a copy up of lower/dir \# rm -fR merged/* This ends up failing with -EPERM after the files in dir has been correctly deleted: unlinkat(4, "2", 0) = 0 unlinkat(4, "1", 0) = 0 unlinkat(4, "3", 0) = 0 close(4) = 0 unlinkat(AT_FDCWD, "merged/dir", AT_REMOVEDIR) = -1 EPERM (Operation not permitted) Interestingly, if you don't place files in merged/dir you can remove it, meaning if upper/dir does not exist, creating the char device file works properly in that same location. This patch uses ovl_sb_creator_cred() to get the cred struct from the superblock mounter and override the old cred with these new ones so that the whiteout creation is possible because overlay is wrong in assuming that the creds it will get with prepare_creds will be in the initial user namespace. The old cap_raise game is removed in favor of just overriding the old cred struct. This patch also drops from ovl_copy_up_one() the following two lines: override_cred->fsuid = stat->uid; override_cred->fsgid = stat->gid; This is because the correct uid and gid are taken directly with the stat struct and correctly set with ovl_set_attr(). Signed-off-by: Antonio Murdaca Signed-off-by: Miklos Szeredi --- fs/overlayfs/copy_up.c | 26 +--------------- fs/overlayfs/dir.c | 67 +++------------------------------------- fs/overlayfs/overlayfs.h | 1 + fs/overlayfs/readdir.c | 14 ++------- fs/overlayfs/super.c | 18 ++++++++++- 5 files changed, 27 insertions(+), 99 deletions(-) diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c index cc514da6f3e7..80aa6f1eb336 100644 --- a/fs/overlayfs/copy_up.c +++ b/fs/overlayfs/copy_up.c @@ -336,7 +336,6 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry, struct dentry *upperdir; struct dentry *upperdentry; const struct cred *old_cred; - struct cred *override_cred; char *link = NULL; if (WARN_ON(!workdir)) @@ -357,28 +356,7 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry, return PTR_ERR(link); } - err = -ENOMEM; - override_cred = prepare_creds(); - if (!override_cred) - goto out_free_link; - - override_cred->fsuid = stat->uid; - override_cred->fsgid = stat->gid; - /* - * CAP_SYS_ADMIN for copying up extended attributes - * CAP_DAC_OVERRIDE for create - * CAP_FOWNER for chmod, timestamp update - * CAP_FSETID for chmod - * CAP_CHOWN for chown - * CAP_MKNOD for mknod - */ - cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN); - cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE); - cap_raise(override_cred->cap_effective, CAP_FOWNER); - cap_raise(override_cred->cap_effective, CAP_FSETID); - cap_raise(override_cred->cap_effective, CAP_CHOWN); - cap_raise(override_cred->cap_effective, CAP_MKNOD); - old_cred = override_creds(override_cred); + old_cred = ovl_override_creds(dentry->d_sb); err = -EIO; if (lock_rename(workdir, upperdir) != NULL) { @@ -401,9 +379,7 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry, out_unlock: unlock_rename(workdir, upperdir); revert_creds(old_cred); - put_cred(override_cred); -out_free_link: if (link) free_page((unsigned long) link); diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index b3fc0a35bf62..22f0253a3567 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -405,28 +405,13 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev, err = ovl_create_upper(dentry, inode, &stat, link, hardlink); } else { const struct cred *old_cred; - struct cred *override_cred; - err = -ENOMEM; - override_cred = prepare_creds(); - if (!override_cred) - goto out_iput; - - /* - * CAP_SYS_ADMIN for setting opaque xattr - * CAP_DAC_OVERRIDE for create in workdir, rename - * CAP_FOWNER for removing whiteout from sticky dir - */ - cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN); - cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE); - cap_raise(override_cred->cap_effective, CAP_FOWNER); - old_cred = override_creds(override_cred); + old_cred = ovl_override_creds(dentry->d_sb); err = ovl_create_over_whiteout(dentry, inode, &stat, link, hardlink); revert_creds(old_cred); - put_cred(override_cred); } if (!err) @@ -662,32 +647,11 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir) if (OVL_TYPE_PURE_UPPER(type)) { err = ovl_remove_upper(dentry, is_dir); } else { - const struct cred *old_cred; - struct cred *override_cred; - - err = -ENOMEM; - override_cred = prepare_creds(); - if (!override_cred) - goto out_drop_write; - - /* - * CAP_SYS_ADMIN for setting xattr on whiteout, opaque dir - * CAP_DAC_OVERRIDE for create in workdir, rename - * CAP_FOWNER for removing whiteout from sticky dir - * CAP_FSETID for chmod of opaque dir - * CAP_CHOWN for chown of opaque dir - */ - cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN); - cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE); - cap_raise(override_cred->cap_effective, CAP_FOWNER); - cap_raise(override_cred->cap_effective, CAP_FSETID); - cap_raise(override_cred->cap_effective, CAP_CHOWN); - old_cred = override_creds(override_cred); + const struct cred *old_cred = ovl_override_creds(dentry->d_sb); err = ovl_remove_and_whiteout(dentry, is_dir); revert_creds(old_cred); - put_cred(override_cred); } out_drop_write: ovl_drop_write(dentry); @@ -725,7 +689,6 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old, bool new_is_dir = false; struct dentry *opaquedir = NULL; const struct cred *old_cred = NULL; - struct cred *override_cred = NULL; err = -EINVAL; if (flags & ~(RENAME_EXCHANGE | RENAME_NOREPLACE)) @@ -794,26 +757,8 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old, old_opaque = !OVL_TYPE_PURE_UPPER(old_type); new_opaque = !OVL_TYPE_PURE_UPPER(new_type); - if (old_opaque || new_opaque) { - err = -ENOMEM; - override_cred = prepare_creds(); - if (!override_cred) - goto out_drop_write; - - /* - * CAP_SYS_ADMIN for setting xattr on whiteout, opaque dir - * CAP_DAC_OVERRIDE for create in workdir - * CAP_FOWNER for removing whiteout from sticky dir - * CAP_FSETID for chmod of opaque dir - * CAP_CHOWN for chown of opaque dir - */ - cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN); - cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE); - cap_raise(override_cred->cap_effective, CAP_FOWNER); - cap_raise(override_cred->cap_effective, CAP_FSETID); - cap_raise(override_cred->cap_effective, CAP_CHOWN); - old_cred = override_creds(override_cred); - } + if (old_opaque || new_opaque) + old_cred = ovl_override_creds(old->d_sb); if (overwrite && OVL_TYPE_MERGE_OR_LOWER(new_type) && new_is_dir) { opaquedir = ovl_check_empty_and_clear(new); @@ -943,10 +888,8 @@ out_dput_old: out_unlock: unlock_rename(new_upperdir, old_upperdir); out_revert_creds: - if (old_opaque || new_opaque) { + if (old_opaque || new_opaque) revert_creds(old_cred); - put_cred(override_cred); - } out_drop_write: ovl_drop_write(old); out: diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index 6a7090f4a441..4cebeb24c08d 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -153,6 +153,7 @@ void ovl_drop_write(struct dentry *dentry); bool ovl_dentry_is_opaque(struct dentry *dentry); void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque); bool ovl_is_whiteout(struct dentry *dentry); +const struct cred *ovl_override_creds(struct super_block *sb); void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry); struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags); diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index 6ec1e43a9a54..e9206bc8598f 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -36,6 +36,7 @@ struct ovl_dir_cache { struct ovl_readdir_data { struct dir_context ctx; + struct dentry *dentry; bool is_lowest; struct rb_root root; struct list_head *list; @@ -206,17 +207,8 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd) struct ovl_cache_entry *p; struct dentry *dentry; const struct cred *old_cred; - struct cred *override_cred; - override_cred = prepare_creds(); - if (!override_cred) - return -ENOMEM; - - /* - * CAP_DAC_OVERRIDE for lookup - */ - cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE); - old_cred = override_creds(override_cred); + old_cred = ovl_override_creds(rdd->dentry->d_sb); err = mutex_lock_killable(&dir->d_inode->i_mutex); if (!err) { @@ -232,7 +224,6 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd) inode_unlock(dir->d_inode); } revert_creds(old_cred); - put_cred(override_cred); return err; } @@ -288,6 +279,7 @@ static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list) struct path realpath; struct ovl_readdir_data rdd = { .ctx.actor = ovl_fill_merge, + .dentry = dentry, .list = list, .root = RB_ROOT, .is_lowest = false, diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 791235e03d17..d659f766ceff 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -42,6 +42,8 @@ struct ovl_fs { long lower_namelen; /* pathnames of lower and upper dirs, for show_options */ struct ovl_config config; + /* creds of process who forced instantiation of super block */ + const struct cred *creator_cred; }; struct ovl_dir_cache; @@ -265,6 +267,13 @@ bool ovl_is_whiteout(struct dentry *dentry) return inode && IS_WHITEOUT(inode); } +const struct cred *ovl_override_creds(struct super_block *sb) +{ + struct ovl_fs *ofs = sb->s_fs_info; + + return override_creds(ofs->creator_cred); +} + static bool ovl_is_opaquedir(struct dentry *dentry) { int res; @@ -603,6 +612,7 @@ static void ovl_put_super(struct super_block *sb) kfree(ufs->config.lowerdir); kfree(ufs->config.upperdir); kfree(ufs->config.workdir); + put_cred(ufs->creator_cred); kfree(ufs); } @@ -1108,10 +1118,14 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) else sb->s_d_op = &ovl_dentry_operations; + ufs->creator_cred = prepare_creds(); + if (!ufs->creator_cred) + goto out_put_lower_mnt; + err = -ENOMEM; oe = ovl_alloc_entry(numlower); if (!oe) - goto out_put_lower_mnt; + goto out_put_cred; root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe)); if (!root_dentry) @@ -1144,6 +1158,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) out_free_oe: kfree(oe); +out_put_cred: + put_cred(ufs->creator_cred); out_put_lower_mnt: for (i = 0; i < ufs->numlower; i++) mntput(ufs->lower_mnt[i]); From 942fd803e6dfc64d32f2ae4f160b2986bc5897b8 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Fri, 27 May 2016 08:55:26 +0200 Subject: [PATCH 2/3] ovl: update documentation Two "fixme" items are actually fixed now. Signed-off-by: Miklos Szeredi --- Documentation/filesystems/overlayfs.txt | 9 --------- 1 file changed, 9 deletions(-) diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt index 28091457b71a..d6259c786316 100644 --- a/Documentation/filesystems/overlayfs.txt +++ b/Documentation/filesystems/overlayfs.txt @@ -194,15 +194,6 @@ If a file with multiple hard links is copied up, then this will "break" the link. Changes will not be propagated to other names referring to the same inode. -Symlinks in /proc/PID/ and /proc/PID/fd which point to a non-directory -object in overlayfs will not contain valid absolute paths, only -relative paths leading up to the filesystem's root. This will be -fixed in the future. - -Some operations are not atomic, for example a crash during copy_up or -rename will leave the filesystem in an inconsistent state. This will -be addressed in the future. - Changes to underlying filesystems --------------------------------- From 21765194cecf2e4514ad75244df459f188140a0f Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Fri, 20 May 2016 09:04:26 -0400 Subject: [PATCH 3/3] ovl: Do d_type check only if work dir creation was successful d_type check requires successful creation of workdir as iterates through work dir and expects work dir to be present in it. If that's not the case, this check will always return d_type not supported even if underlying filesystem might be supporting it. So don't do this check if work dir creation failed in previous step. Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi --- fs/overlayfs/super.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index d659f766ceff..781e1d86d2ce 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -1074,16 +1074,19 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) /* * Upper should support d_type, else whiteouts are visible. * Given workdir and upper are on same fs, we can do - * iterate_dir() on workdir. + * iterate_dir() on workdir. This check requires successful + * creation of workdir in previous step. */ - err = ovl_check_d_type_supported(&workpath); - if (err < 0) - goto out_put_workdir; + if (ufs->workdir) { + err = ovl_check_d_type_supported(&workpath); + if (err < 0) + goto out_put_workdir; - if (!err) { - pr_err("overlayfs: upper fs needs to support d_type.\n"); - err = -EINVAL; - goto out_put_workdir; + if (!err) { + pr_err("overlayfs: upper fs needs to support d_type.\n"); + err = -EINVAL; + goto out_put_workdir; + } } }