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kernfs: fix xattr name handling in LSM helpers

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The implementation of kernfs_security_xattr_*() helpers reuses the
kernfs_node_xattr_*() functions, which take the suffix of the xattr name
and extract full xattr name from it using xattr_full_name(). However,
this function relies on the fact that the suffix passed to xattr
handlers from VFS is always constructed from the full name by just
incerementing the pointer. This doesn't necessarily hold for the callers
of kernfs_security_xattr_*(), so their usage will easily lead to
out-of-bounds access.

Fix this by moving the xattr name reconstruction to the VFS xattr
handlers and replacing the kernfs_security_xattr_*() helpers with more
general kernfs_xattr_*() helpers that take full xattr name and allow
accessing all kernfs node's xattrs.

Reported-by: kernel test robot <[email protected]>
Fixes: b230d5aba2 ("LSM: add new hook for kernfs node initialization")
Fixes: ec882da5cd ("selinux: implement the kernfs_init_security hook")
Signed-off-by: Ondrej Mosnacek <[email protected]>
Signed-off-by: Paul Moore <[email protected]>
This commit is contained in:
Ondrej Mosnacek 2019-04-03 09:29:41 +02:00 • committed by Paul Moore
commit 1537ad15c9
3 changed files with 33 additions and 56 deletions
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9
security/selinux/hooks.c
View file

@ -3394,7 +3394,7 @@ static int selinux_kernfs_init_security(struct kernfs_node *kn_dir,
int rc;
char *context;
rc = kernfs_security_xattr_get(kn_dir, XATTR_SELINUX_SUFFIX, NULL, 0);
rc = kernfs_xattr_get(kn_dir, XATTR_NAME_SELINUX, NULL, 0);
if (rc == -ENODATA)
return 0;
else if (rc < 0)
@ -3405,8 +3405,7 @@ static int selinux_kernfs_init_security(struct kernfs_node *kn_dir,
if (!context)
return -ENOMEM;
rc = kernfs_security_xattr_get(kn_dir, XATTR_SELINUX_SUFFIX, context,
clen);
rc = kernfs_xattr_get(kn_dir, XATTR_NAME_SELINUX, context, clen);
if (rc < 0) {
kfree(context);
return rc;
@ -3439,8 +3438,8 @@ static int selinux_kernfs_init_security(struct kernfs_node *kn_dir,
if (rc)
return rc;
rc = kernfs_security_xattr_set(kn, XATTR_SELINUX_SUFFIX, context, clen,
XATTR_CREATE);
rc = kernfs_xattr_set(kn, XATTR_NAME_SELINUX, context, clen,
XATTR_CREATE);
kfree(context);
return rc;
}