sysfs: Update sysfs_setxattr so it updates secdata under the sysfs_mutex

The sysfs_mutex is required to ensure updates are and will remain
atomic with respect to other inode iattr updates, that do not happen
through the filesystem.

Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 29 insertions, 12 deletions

diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index e1443518398e..000bd9865004 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -123,23 +123,39 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
         return error;
 }
 
+static int sysfs_sd_setsecdata(struct sysfs_dirent *sd, void **secdata, u32 *secdata_len)
+{
+        struct sysfs_inode_attrs *iattrs;
+        void *old_secdata;
+        size_t old_secdata_len;
+
+        iattrs = sd->s_iattr;
+        if (!iattrs)
+                iattrs = sysfs_init_inode_attrs(sd);
+        if (!iattrs)
+                return -ENOMEM;
+
+        old_secdata = iattrs->ia_secdata;
+        old_secdata_len = iattrs->ia_secdata_len;
+
+        iattrs->ia_secdata = *secdata;
+        iattrs->ia_secdata_len = *secdata_len;
+
+        *secdata = old_secdata;
+        *secdata_len = old_secdata_len;
+        return 0;
+}
+
 int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
                 size_t size, int flags)
 {
         struct sysfs_dirent *sd = dentry->d_fsdata;
-        struct sysfs_inode_attrs *iattrs;
         void *secdata;
         int error;
         u32 secdata_len = 0;
 
         if (!sd)
                 return -EINVAL;
-        if (!sd->s_iattr)
-                sd->s_iattr = sysfs_init_inode_attrs(sd);
-        if (!sd->s_iattr)
-                return -ENOMEM;
-
-        iattrs = sd->s_iattr;
 
         if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN)) {
                 const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
@@ -151,12 +167,13 @@ int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
                                                 &secdata, &secdata_len);
                 if (error)
                         goto out;
-                if (iattrs->ia_secdata)
-                        security_release_secctx(iattrs->ia_secdata,
-                                                iattrs->ia_secdata_len);
-                iattrs->ia_secdata = secdata;
-                iattrs->ia_secdata_len = secdata_len;
 
+                mutex_lock(&sysfs_mutex);
+                error = sysfs_sd_setsecdata(sd, &secdata, &secdata_len);
+                mutex_unlock(&sysfs_mutex);
+
+                if (secdata)
+                        security_release_secctx(secdata, secdata_len);
         } else
                 return -EINVAL;
 out: