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Message-Id: <20210112220124.837960-36-christian.brauner@ubuntu.com>
Date: Tue, 12 Jan 2021 23:01:17 +0100
From: Christian Brauner <christian.brauner@...ntu.com>
To: Alexander Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@...radead.org>,
linux-fsdevel@...r.kernel.org
Cc: John Johansen <john.johansen@...onical.com>,
James Morris <jmorris@...ei.org>,
Mimi Zohar <zohar@...ux.ibm.com>,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Casey Schaufler <casey@...aufler-ca.com>,
Arnd Bergmann <arnd@...db.de>,
Andreas Dilger <adilger.kernel@...ger.ca>,
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
Geoffrey Thomas <geofft@...reload.com>,
Mrunal Patel <mpatel@...hat.com>,
Josh Triplett <josh@...htriplett.org>,
Andy Lutomirski <luto@...nel.org>,
Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
Tycho Andersen <tycho@...ho.ws>,
David Howells <dhowells@...hat.com>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Seth Forshee <seth.forshee@...onical.com>,
Stéphane Graber <stgraber@...ntu.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Aleksa Sarai <cyphar@...har.com>,
Lennart Poettering <lennart@...ttering.net>,
"Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
Kees Cook <keescook@...omium.org>,
Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>,
Jonathan Corbet <corbet@....net>,
containers@...ts.linux-foundation.org,
linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
Christian Brauner <christian.brauner@...ntu.com>,
Christoph Hellwig <hch@....de>
Subject: [PATCH v5 35/42] fat: handle idmapped mounts
Let fat handle idmapped mounts. This allows to have the same fat mount
appear in multiple locations with different id mappings. This allows to
expose a vfat formatted USB stick to multiple user with different ids on
the host or in user namespaces allowing for dac permissions:
mount -o uid=1000,gid=1000 /dev/sdb /mnt
u1001@...vm:/lower1$ ls -ln /mnt/
total 4
-rwxr-xr-x 1 1000 1000 4 Oct 28 03:44 aaa
-rwxr-xr-x 1 1000 1000 0 Oct 28 01:09 bbb
-rwxr-xr-x 1 1000 1000 0 Oct 28 01:10 ccc
-rwxr-xr-x 1 1000 1000 0 Oct 28 03:46 ddd
-rwxr-xr-x 1 1000 1000 0 Oct 28 04:01 eee
mount-idmapped --map-mount b:1000:1001:1
u1001@...vm:/lower1$ ls -ln /lower1/
total 4
-rwxr-xr-x 1 1001 1001 4 Oct 28 03:44 aaa
-rwxr-xr-x 1 1001 1001 0 Oct 28 01:09 bbb
-rwxr-xr-x 1 1001 1001 0 Oct 28 01:10 ccc
-rwxr-xr-x 1 1001 1001 0 Oct 28 03:46 ddd
-rwxr-xr-x 1 1001 1001 0 Oct 28 04:01 eee
u1001@...vm:/lower1$ touch /lower1/fff
u1001@...vm:/lower1$ ls -ln /lower1/fff
-rwxr-xr-x 1 1001 1001 0 Oct 28 04:03 /lower1/fff
u1001@...vm:/lower1$ ls -ln /mnt/fff
-rwxr-xr-x 1 1000 1000 0 Oct 28 04:03 /mnt/fff
Cc: Christoph Hellwig <hch@....de>
Cc: David Howells <dhowells@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
/* v2 */
unchanged
/* v3 */
unchanged
/* v4 */
- Mauricio Vásquez Bernal <mauricio@...volk.io>:
- Fix mount example in commit message.
- Serge Hallyn <serge@...lyn.com>:
- Use "mnt_userns" to refer to a vfsmount's userns everywhere to make
terminology consistent.
/* v5 */
base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837
---
fs/fat/file.c | 15 ++++++++-------
fs/fat/namei_msdos.c | 2 +-
fs/fat/namei_vfat.c | 2 +-
3 files changed, 10 insertions(+), 9 deletions(-)
diff --git a/fs/fat/file.c b/fs/fat/file.c
index 80fbf1b5bb6c..107e9ece1a7c 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -398,7 +398,7 @@ int fat_getattr(struct user_namespace *mnt_userns, const struct path *path,
struct kstat *stat, u32 request_mask, unsigned int flags)
{
struct inode *inode = d_inode(path->dentry);
- generic_fillattr(&init_user_ns, inode, stat);
+ generic_fillattr(mnt_userns, inode, stat);
stat->blksize = MSDOS_SB(inode->i_sb)->cluster_size;
if (MSDOS_SB(inode->i_sb)->options.nfs == FAT_NFS_NOSTALE_RO) {
@@ -447,12 +447,13 @@ static int fat_sanitize_mode(const struct msdos_sb_info *sbi,
return 0;
}
-static int fat_allow_set_time(struct msdos_sb_info *sbi, struct inode *inode)
+static int fat_allow_set_time(struct user_namespace *mnt_userns,
+ struct msdos_sb_info *sbi, struct inode *inode)
{
umode_t allow_utime = sbi->options.allow_utime;
- if (!uid_eq(current_fsuid(), inode->i_uid)) {
- if (in_group_p(inode->i_gid))
+ if (!uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode))) {
+ if (in_group_p(i_gid_into_mnt(mnt_userns, inode)))
allow_utime >>= 3;
if (allow_utime & MAY_WRITE)
return 1;
@@ -477,11 +478,11 @@ int fat_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
/* Check for setting the inode time. */
ia_valid = attr->ia_valid;
if (ia_valid & TIMES_SET_FLAGS) {
- if (fat_allow_set_time(sbi, inode))
+ if (fat_allow_set_time(mnt_userns, sbi, inode))
attr->ia_valid &= ~TIMES_SET_FLAGS;
}
- error = setattr_prepare(&init_user_ns, dentry, attr);
+ error = setattr_prepare(mnt_userns, dentry, attr);
attr->ia_valid = ia_valid;
if (error) {
if (sbi->options.quiet)
@@ -551,7 +552,7 @@ int fat_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
fat_truncate_time(inode, &attr->ia_mtime, S_MTIME);
attr->ia_valid &= ~(ATTR_ATIME|ATTR_CTIME|ATTR_MTIME);
- setattr_copy(&init_user_ns, inode, attr);
+ setattr_copy(mnt_userns, inode, attr);
mark_inode_dirty(inode);
out:
return error;
diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index a8f3375d9d10..efba301d68ae 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -667,7 +667,7 @@ static struct file_system_type msdos_fs_type = {
.name = "msdos",
.mount = msdos_mount,
.kill_sb = kill_block_super,
- .fs_flags = FS_REQUIRES_DEV,
+ .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
};
MODULE_ALIAS_FS("msdos");
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 23936ecf79a5..5369d82e0bfb 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1063,7 +1063,7 @@ static struct file_system_type vfat_fs_type = {
.name = "vfat",
.mount = vfat_mount,
.kill_sb = kill_block_super,
- .fs_flags = FS_REQUIRES_DEV,
+ .fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
};
MODULE_ALIAS_FS("vfat");
--
2.30.0
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