[PATCH] xattr: Fix error results for non-existent / invisible attributes

Andreas Gruenbacher
2011-05-27T12:59:59Z

Return -ENODATA when trying to read a user.* attribute which cannot
exist: user space otherwise does not have a reasonable way to
distinguish between non-existent and inaccessible attributes.

Likewise, return -ENODATA when an unprivileged process tries to read a
trusted.* attribute: to unprivileged processes, those attributes are
invisible (listxattr() won't include them).

Related to this bug report: https://bugzilla.redhat.com/660613

Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
---
fs/xattr.c | 16 ++++++++++------
1 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index f1ef949..4be2e76 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -46,18 +46,22 @@ xattr_permission(struct inode *inode, const char *name, int mask)
return 0;

/*
- * The trusted.* namespace can only be accessed by a privileged user.
+ * The trusted.* namespace can only be accessed by privileged users.
*/
- if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
- return (capable(CAP_SYS_ADMIN) ? 0 : -EPERM);
+ if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
+ if (!capable(CAP_SYS_ADMIN))
+ return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
+ return 0;
+ }

- /* In user.* namespace, only regular files and directories can have
+ /*
+ * In the user.* namespace, only regular files and directories can have
* extended attributes. For sticky directories, only the owner and
- * privileged user can write attributes.
+ * privileged users can write attributes.
*/
if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
- return -EPERM;
+ return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
(mask & MAY_WRITE) && !inode_owner_or_capable(inode))
return -EPERM;
--
1.7.1