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/20210112220124.837960-36-christian.brauner@xxxxxxxxxx Cc: Christoph Hellwig <hch@xxxxxx> Cc: David Howells <dhowells@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: linux-fsdevel@xxxxxxxxxxxxxxx Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx> --- /* v2 */ unchanged /* v3 */ unchanged /* v4 */ - Mauricio Vásquez Bernal <mauricio@xxxxxxxxxx>: - Fix mount example in commit message. - Serge Hallyn <serge@xxxxxxxxxx>: - Use "mnt_userns" to refer to a vfsmount's userns everywhere to make terminology consistent. /* v5 */ unchanged base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837 /* v6 */ unchanged base-commit: 19c329f6808995b142b3966301f217c831e7cf31 --- 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 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"); -- 2.30.0
