lkml.org 
[lkml]   [2011]   [Oct]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH -V7 09/26] vfs: Add delete child and delete self permission flags
    On Tue, Oct 18, 2011 at 09:02:44PM +0530, Aneesh Kumar K.V wrote:
    > From: Andreas Gruenbacher <agruen@kernel.org>
    >
    > Normally, deleting a file requires write access to the parent directory.
    > Some permission models use a different permission on the parent
    > directory to indicate delete access. In addition, a process can have
    > per-file delete access even without delete access on the parent
    > directory.
    >
    > Introduce two new inode_permission() mask flags and use them in
    > may_delete()
    >
    > Acked-by: David Howells <dhowells@redhat.com>
    > Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
    > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    > ---
    > fs/namei.c | 42 ++++++++++++++++++++++++++++--------------
    > include/linux/fs.h | 2 ++
    > 2 files changed, 30 insertions(+), 14 deletions(-)
    >
    > diff --git a/fs/namei.c b/fs/namei.c
    > index f6184b8..7bf42e8 100644
    > --- a/fs/namei.c
    > +++ b/fs/namei.c
    > @@ -337,7 +337,7 @@ static inline int do_inode_permission(struct inode *inode, int mask)
    > * are used for other things.
    > *
    > * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
    > - * MAY_WRITE must also be set in @mask.
    > + * MAY_DELETE_CHILD, MAY_DELETE_SELF, MAY_WRITE must also be set in @mask.
    > */
    > int inode_permission(struct inode *inode, int mask)
    > {
    > @@ -1853,7 +1853,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
    > return 0;
    >
    > other_userns:
    > - return !ns_capable(inode_userns(inode), CAP_FOWNER);
    > + return 1;
    > }
    >
    > /*
    > @@ -1875,30 +1875,44 @@ other_userns:
    > * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
    > * nfs_async_unlink().
    > */
    > -static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
    > +static int may_delete(struct inode *dir, struct dentry *victim,
    > + int isdir, int replace)
    > {
    > - int error;
    > + struct inode *inode = victim->d_inode;
    > + int mask, replace_mask = 0, error, is_sticky;
    > +
    >
    > - if (!victim->d_inode)
    > + if (!inode)
    > return -ENOENT;
    >
    > BUG_ON(victim->d_parent->d_inode != dir);
    > audit_inode_child(victim, dir);
    >
    > - error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
    > + mask = MAY_WRITE | MAY_EXEC | MAY_DELETE_CHILD;
    > + if (replace)
    > + replace_mask = S_ISDIR(inode->i_mode) ?
    > + MAY_CREATE_DIR : MAY_CREATE_FILE;
    > + is_sticky = check_sticky(dir, inode);
    > + error = inode_permission(dir, mask | replace_mask);
    > + if ((error || is_sticky) && IS_RICHACL(inode) &&
    > + (inode_permission(dir, MAY_EXEC | replace_mask) == 0) &&
    > + (inode_permission(inode, MAY_DELETE_SELF) == 0))
    > + error = 0;
    > + else if (!error && is_sticky &&
    > + !ns_capable(inode_userns(inode), CAP_FOWNER))
    > + error = -EPERM;

    Maybe I'm dense, but that big if-else-if is still giving me a headache.

    The point is just to delay the ns_capable() check to avoid setting
    PF_SUPERPRIV in cases where we weren't before?

    How about putting using a helper function for the richacl check, and
    calling it from check_sticky instead? That makes the above:

    error = inode_permission(dir, mask | replace_mask);
    if (error && !richacl_may_delete(dir, inode, replace_mask))
    return error;
    if (check_sticky(dir, inode, replace_mask))
    return -EPERM;

    (As in the following--totally untested and possibly wrong.)

    Also: the comment before may_delete() needs updating.

    --b.

    commit 7fe4b12ba6b914167ed1f1bc617af04eecbce7d1
    Author: Andreas Gruenbacher <agruen@kernel.org>
    Date: Tue Oct 18 15:17:50 2011 +0530

    vfs: Add delete child and delete self permission flags

    Normally, deleting a file requires write access to the parent directory.
    Some permission models use a different permission on the parent
    directory to indicate delete access. In addition, a process can have
    per-file delete access even without delete access on the parent
    directory.

    Introduce two new inode_permission() mask flags and use them in
    may_delete()

    Acked-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

    diff --git a/fs/namei.c b/fs/namei.c
    index f6184b8..f0cccd9 100644
    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -337,7 +337,7 @@ static inline int do_inode_permission(struct inode *inode, int mask)
    * are used for other things.
    *
    * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
    - * MAY_WRITE must also be set in @mask.
    + * MAY_DELETE_CHILD, MAY_DELETE_SELF, MAY_WRITE must also be set in @mask.
    */
    int inode_permission(struct inode *inode, int mask)
    {
    @@ -1835,11 +1835,18 @@ static int user_path_parent(int dfd, const char __user *path,
    return error;
    }

    +static bool richacl_may_delete(struct inode *dir, struct inode *inode, int replace_mask)
    +{
    + return IS_RICHACL(inode)
    + && (inode_permission(dir, MAY_EXEC | replace_mask) == 0)
    + && (inode_permission(inode, MAY_DELETE_SELF) == 0);
    +}
    +
    /*
    * It's inline, so penalty for filesystems that don't use sticky bit is
    * minimal.
    */
    -static inline int check_sticky(struct inode *dir, struct inode *inode)
    +static inline int check_sticky(struct inode *dir, struct inode *inode, int replace_mask)
    {
    uid_t fsuid = current_fsuid();

    @@ -1851,7 +1858,8 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
    return 0;
    if (dir->i_uid == fsuid)
    return 0;
    -
    + if (richacl_may_delete(dir, inode, replace_mask))
    + return 0;
    other_userns:
    return !ns_capable(inode_userns(inode), CAP_FOWNER);
    }
    @@ -1875,30 +1883,38 @@ other_userns:
    * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
    * nfs_async_unlink().
    */
    -static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
    +static int may_delete(struct inode *dir, struct dentry *victim,
    + int isdir, int replace)
    {
    - int error;
    + struct inode *inode = victim->d_inode;
    + int mask, replace_mask = 0, error;
    +

    - if (!victim->d_inode)
    + if (!inode)
    return -ENOENT;

    BUG_ON(victim->d_parent->d_inode != dir);
    audit_inode_child(victim, dir);

    - error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
    - if (error)
    + mask = MAY_WRITE | MAY_EXEC | MAY_DELETE_CHILD;
    + if (replace)
    + replace_mask = S_ISDIR(inode->i_mode) ?
    + MAY_CREATE_DIR : MAY_CREATE_FILE;
    + error = inode_permission(dir, mask | replace_mask);
    + if (error && !richacl_may_delete(dir, inode, replace_mask))
    return error;
    + if (check_sticky(dir, inode, replace_mask))
    + return -EPERM;
    if (IS_APPEND(dir))
    return -EPERM;
    - if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||
    - IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))
    + if (IS_APPEND(inode) || IS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
    return -EPERM;
    if (isdir) {
    - if (!S_ISDIR(victim->d_inode->i_mode))
    + if (!S_ISDIR(inode->i_mode))
    return -ENOTDIR;
    if (IS_ROOT(victim))
    return -EBUSY;
    - } else if (S_ISDIR(victim->d_inode->i_mode))
    + } else if (S_ISDIR(inode->i_mode))
    return -EISDIR;
    if (IS_DEADDIR(dir))
    return -ENOENT;
    @@ -2605,7 +2621,7 @@ void dentry_unhash(struct dentry *dentry)

    int vfs_rmdir(struct inode *dir, struct dentry *dentry)
    {
    - int error = may_delete(dir, dentry, 1);
    + int error = may_delete(dir, dentry, 1, 0);

    if (error)
    return error;
    @@ -2700,7 +2716,7 @@ SYSCALL_DEFINE1(rmdir, const char __user *, pathname)

    int vfs_unlink(struct inode *dir, struct dentry *dentry)
    {
    - int error = may_delete(dir, dentry, 0);
    + int error = may_delete(dir, dentry, 0, 0);

    if (error)
    return error;
    @@ -3096,14 +3112,14 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
    if (old_dentry->d_inode == new_dentry->d_inode)
    return 0;

    - error = may_delete(old_dir, old_dentry, is_dir);
    + error = may_delete(old_dir, old_dentry, is_dir, 0);
    if (error)
    return error;

    if (!new_dentry->d_inode)
    error = may_create(new_dir, new_dentry, is_dir);
    else
    - error = may_delete(new_dir, new_dentry, is_dir);
    + error = may_delete(new_dir, new_dentry, is_dir, 1);
    if (error)
    return error;

    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index 60361c6..ccece40 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -69,6 +69,8 @@ struct inodes_stat_t {
    #define MAY_NOT_BLOCK 0x00000080
    #define MAY_CREATE_FILE 0x00000100
    #define MAY_CREATE_DIR 0x00000200
    +#define MAY_DELETE_CHILD 0x00000400
    +#define MAY_DELETE_SELF 0x00000800

    /*
    * flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond

    \
     
     \ /
      Last update: 2011-10-20 00:11    [W:0.038 / U:6.888 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site