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authorChristian Brauner <christian.brauner@ubuntu.com>2021-01-21 14:19:56 +0100
committerChristian Brauner <christian.brauner@ubuntu.com>2021-01-24 14:43:46 +0100
commit4b78993681083361f19f66b4e9db298945647a3d (patch)
tree8da220e6162c1d5326f0f468d5b32e2e5b42022b /fs/fat
parent01eadc8dd96d7215dda71a1fe74b07b0e3b48af5 (diff)
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@f2-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@f2-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@f2-vm:/lower1$ touch /lower1/fff u1001@f2-vm:/lower1$ ls -ln /lower1/fff -rwxr-xr-x 1 1001 1001 0 Oct 28 04:03 /lower1/fff u1001@f2-vm:/lower1$ ls -ln /mnt/fff -rwxr-xr-x 1 1000 1000 0 Oct 28 04:03 /mnt/fff Link: https://lore.kernel.org/r/20210121131959.646623-38-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Diffstat (limited to 'fs/fat')
-rw-r--r--fs/fat/file.c15
-rw-r--r--fs/fat/namei_msdos.c2
-rw-r--r--fs/fat/namei_vfat.c2
3 files changed, 10 insertions, 9 deletions
diff --git a/fs/fat/file.c b/fs/fat/file.c
index dd73d1b70c55..da7c56234189 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");