Re: [PATCH v14 03/22] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags
From: Andreas Dilger <hidden>
Date: 2015-11-06 21:26:45
Also in:
linux-cifs, linux-ext4, linux-fsdevel, linux-nfs, linux-xfs, lkml
On Nov 5, 2015, at 4:39 AM, Andreas Gruenbacher [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Normally, deleting a file requires MAY_WRITE access to the parent directory. With richacls, a file may be deleted with MAY_DELETE_CHILD access to the parent directory or with MAY_DELETE_SELF access to the file. To support that, pass the MAY_DELETE_CHILD mask flag to inode_permission() when checking for delete access inside a directory, and MAY_DELETE_SELF when checking for delete access to a file itelf. The MAY_DELETE_SELF permission overrides the sticky directory check. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Reviewed-by: J. Bruce Fields <redacted> --- fs/namei.c | 21 ++++++++++++--------- include/linux/fs.h | 2 ++ 2 files changed, 14 insertions(+), 9 deletions(-)diff --git a/fs/namei.c b/fs/namei.c index 0259392..2eab19e 100644 --- a/fs/namei.c +++ b/fs/namei.c@@ -453,9 +453,9 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask) * this, letting us set arbitrary permissions for filesystem access without * changing the "normal" UIDs which are used for other things. * - * MAY_WRITE must be set in @mask whenever MAY_APPEND, MAY_CREATE_FILE, or - * MAY_CREATE_DIR are set. That way, file systems that don't support these - * permissions will check for MAY_WRITE instead. + * MAY_WRITE must be set in @mask whenever MAY_APPEND, MAY_CREATE_FILE, + * MAY_CREATE_DIR, or MAY_DELETE_CHILD are set. That way, file systems that + * don't support these permissions will check for MAY_WRITE instead. */int inode_permission(struct inode *inode, int mask) {@@ -2555,7 +2555,7 @@ static int may_delete(struct inode *dir, struct dentry *victim,bool isdir, bool replace) { struct inode *inode = d_backing_inode(victim); - int error, mask = MAY_WRITE | MAY_EXEC; + int error, mask = MAY_EXEC; if (d_is_negative(victim)) return -ENOENT;@@ -2565,15 +2565,18 @@ static int may_delete(struct inode *dir, struct dentry *victim,audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE); if (replace) - mask |= isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE; - error = inode_permission(dir, mask); + mask |= MAY_WRITE | (isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE); + error = inode_permission(dir, mask | MAY_WRITE | MAY_DELETE_CHILD); + if (!error && check_sticky(dir, inode)) + error = -EPERM; + if (error && IS_RICHACL(inode) && + inode_permission(inode, MAY_DELETE_SELF) == 0) + error = 0;
This looks like a serious bug, as it is overriding other errors returned from inode_permission() such as -EROFS from sb_permission() or even from generic_permission->acl_permission_check(). Clearing the error returned by an earlier check doesn't seem safe, only new errors should be added. The call to inode_permission(inode) is also duplicating the sb_permission() check from inode_permission(dir), so at most should be __inode_permission(). It looks like this would be correct if you check MAY_DELETE_SELF together with check_sticky(): if (!error && check_sticky(dir, inode) && !__inode_permission(inode, MAY_DELETE_SELF)) error = -EPERM; I ommitted the IS_RICHACL() check here, since that should probably be in __inode_permission() when MAY_DELETE_SELF is passed? Cheers, Andreas
if (error) return error; if (IS_APPEND(dir)) return -EPERM;
- - if (check_sticky(dir, inode) || IS_APPEND(inode) || - IS_IMMUTABLE(inode) || IS_SWAPFILE(inode)) + if (IS_APPEND(inode) || IS_IMMUTABLE(inode) || IS_SWAPFILE(inode)) return -EPERM;
quoted hunk ↗ jump to hunk
if (isdir) { if (!d_is_dir(victim))diff --git a/include/linux/fs.h b/include/linux/fs.h index d6e2330..402acd7 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h@@ -84,6 +84,8 @@ typedef void (dax_iodone_t)(struct buffer_head *bh_map, int uptodate);#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 -- 2.5.0
Cheers, Andreas