From: Christoph Hellwig The xattr code has rather complex permission checks because the rules are very different for different attribute namespaces. This patch moves as much as we can into the generic code. Currenyly all the major disk based filesystems duplicate these checks, while many minor filesystems or network filesystems lack some or all of them. To do this we need defines for the extended attribute names in common code, I moved them up from JFS which had the nicest defintions. Signed-off-by: Christoph Hellwig Signed-off-by: Andrew Morton --- fs/jfs/xattr.c | 15 ------------ fs/xattr.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++---- include/linux/xattr.h | 15 ++++++++++++ 3 files changed, 72 insertions(+), 19 deletions(-) diff -puN fs/jfs/xattr.c~move-xattr-permission-checks-into-the-vfs fs/jfs/xattr.c --- devel/fs/jfs/xattr.c~move-xattr-permission-checks-into-the-vfs 2005-11-15 00:05:54.000000000 -0800 +++ devel-akpm/fs/jfs/xattr.c 2005-11-15 00:05:54.000000000 -0800 @@ -83,21 +83,6 @@ struct ea_buffer { #define EA_NEW 0x0004 #define EA_MALLOC 0x0008 -/* Namespaces */ -#define XATTR_SYSTEM_PREFIX "system." -#define XATTR_SYSTEM_PREFIX_LEN (sizeof (XATTR_SYSTEM_PREFIX) - 1) - -#define XATTR_USER_PREFIX "user." -#define XATTR_USER_PREFIX_LEN (sizeof (XATTR_USER_PREFIX) - 1) - -#define XATTR_OS2_PREFIX "os2." -#define XATTR_OS2_PREFIX_LEN (sizeof (XATTR_OS2_PREFIX) - 1) - -/* XATTR_SECURITY_PREFIX is defined in include/linux/xattr.h */ -#define XATTR_SECURITY_PREFIX_LEN (sizeof (XATTR_SECURITY_PREFIX) - 1) - -#define XATTR_TRUSTED_PREFIX "trusted." -#define XATTR_TRUSTED_PREFIX_LEN (sizeof (XATTR_TRUSTED_PREFIX) - 1) /* * These three routines are used to recognize on-disk extended attributes diff -puN fs/xattr.c~move-xattr-permission-checks-into-the-vfs fs/xattr.c --- devel/fs/xattr.c~move-xattr-permission-checks-into-the-vfs 2005-11-15 00:05:54.000000000 -0800 +++ devel-akpm/fs/xattr.c 2005-11-15 00:05:54.000000000 -0800 @@ -20,6 +20,47 @@ #include +/* + * Check permissions for extended attribute access. This is a bit complicated + * because different namespaces have very different rules. + */ +static int +xattr_permission(struct inode *inode, const char *name, int mask) +{ + /* + * We can never set or remove an extended attribute on a read-only + * filesystem or on an immutable / append-only inode. + */ + if (mask & MAY_WRITE) { + if (IS_RDONLY(inode)) + return -EROFS; + if (IS_IMMUTABLE(inode) || IS_APPEND(inode)) + return -EPERM; + } + + /* + * No restriction for security.* and system.* from the VFS. Decision + * on these is left to the underlying filesystem / security module. + */ + if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) || + !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN)) + return 0; + + /* + * The trusted.* namespace can only accessed by a privilegued user. + */ + if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) + return (capable(CAP_SYS_ADMIN) ? 0 : -EPERM); + + if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) { + if (!S_ISREG(inode->i_mode) && + (!S_ISDIR(inode->i_mode) || inode->i_mode & S_ISVTX)) + return -EPERM; + } + + return permission(inode, mask, NULL); +} + int vfs_setxattr(struct dentry *dentry, char *name, void *value, size_t size, int flags) @@ -27,6 +68,10 @@ vfs_setxattr(struct dentry *dentry, char struct inode *inode = dentry->d_inode; int error; + error = xattr_permission(inode, name, MAY_WRITE); + if (error) + return error; + down(&inode->i_sem); error = security_inode_setxattr(dentry, name, value, size, flags); if (error) @@ -40,8 +85,8 @@ vfs_setxattr(struct dentry *dentry, char size, flags); } } else if (!strncmp(name, XATTR_SECURITY_PREFIX, - sizeof XATTR_SECURITY_PREFIX - 1)) { - const char *suffix = name + sizeof XATTR_SECURITY_PREFIX - 1; + XATTR_SECURITY_PREFIX_LEN)) { + const char *suffix = name + XATTR_SECURITY_PREFIX_LEN; error = security_inode_setsecurity(inode, suffix, value, size, flags); if (!error) @@ -59,6 +104,10 @@ vfs_getxattr(struct dentry *dentry, char struct inode *inode = dentry->d_inode; int error; + error = xattr_permission(inode, name, MAY_READ); + if (error) + return error; + error = security_inode_getxattr(dentry, name); if (error) return error; @@ -69,8 +118,8 @@ vfs_getxattr(struct dentry *dentry, char error = -EOPNOTSUPP; if (!strncmp(name, XATTR_SECURITY_PREFIX, - sizeof XATTR_SECURITY_PREFIX - 1)) { - const char *suffix = name + sizeof XATTR_SECURITY_PREFIX - 1; + XATTR_SECURITY_PREFIX_LEN)) { + const char *suffix = name + XATTR_SECURITY_PREFIX_LEN; int ret = security_inode_getsecurity(inode, suffix, value, size, error); /* @@ -94,6 +143,10 @@ vfs_removexattr(struct dentry *dentry, c if (!inode->i_op->removexattr) return -EOPNOTSUPP; + error = xattr_permission(inode, name, MAY_WRITE); + if (error) + return error; + error = security_inode_removexattr(dentry, name); if (error) return error; diff -puN include/linux/xattr.h~move-xattr-permission-checks-into-the-vfs include/linux/xattr.h --- devel/include/linux/xattr.h~move-xattr-permission-checks-into-the-vfs 2005-11-15 00:05:54.000000000 -0800 +++ devel-akpm/include/linux/xattr.h 2005-11-15 00:05:54.000000000 -0800 @@ -13,7 +13,22 @@ #define XATTR_CREATE 0x1 /* set value, fail if attr already exists */ #define XATTR_REPLACE 0x2 /* set value, fail if attr does not exist */ +/* Namespaces */ +#define XATTR_OS2_PREFIX "os2." +#define XATTR_OS2_PREFIX_LEN (sizeof (XATTR_OS2_PREFIX) - 1) + #define XATTR_SECURITY_PREFIX "security." +#define XATTR_SECURITY_PREFIX_LEN (sizeof (XATTR_SECURITY_PREFIX) - 1) + +#define XATTR_SYSTEM_PREFIX "system." +#define XATTR_SYSTEM_PREFIX_LEN (sizeof (XATTR_SYSTEM_PREFIX) - 1) + +#define XATTR_TRUSTED_PREFIX "trusted." +#define XATTR_TRUSTED_PREFIX_LEN (sizeof (XATTR_TRUSTED_PREFIX) - 1) + +#define XATTR_USER_PREFIX "user." +#define XATTR_USER_PREFIX_LEN (sizeof (XATTR_USER_PREFIX) - 1) + struct xattr_handler { char *prefix; _