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    Subject[PATCH AUTOSEL 5.6 04/47] evm: Fix RCU list related warnings
    Date
    From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

    [ Upstream commit 770f60586d2af0590be263f55fd079226313922c ]

    This patch fixes the following warning and few other instances of
    traversal of evm_config_xattrnames list:

    [ 32.848432] =============================
    [ 32.848707] WARNING: suspicious RCU usage
    [ 32.848966] 5.7.0-rc1-00006-ga8d5875ce5f0b #1 Not tainted
    [ 32.849308] -----------------------------
    [ 32.849567] security/integrity/evm/evm_main.c:231 RCU-list traversed in non-reader section!!

    Since entries are only added to the list and never deleted, use
    list_for_each_entry_lockless() instead of list_for_each_entry_rcu for
    traversing the list. Also, add a relevant comment in evm_secfs.c to
    indicate this fact.

    Reported-by: kernel test robot <lkp@intel.com>
    Suggested-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
    Acked-by: Paul E. McKenney <paulmck@kernel.org> (RCU viewpoint)
    Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    security/integrity/evm/evm_crypto.c | 2 +-
    security/integrity/evm/evm_main.c | 4 ++--
    security/integrity/evm/evm_secfs.c | 9 ++++++++-
    3 files changed, 11 insertions(+), 4 deletions(-)

    diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
    index cc826c2767a3..fbc2ee6d46fc 100644
    --- a/security/integrity/evm/evm_crypto.c
    +++ b/security/integrity/evm/evm_crypto.c
    @@ -209,7 +209,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
    data->hdr.length = crypto_shash_digestsize(desc->tfm);

    error = -ENODATA;
    - list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
    + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
    bool is_ima = false;

    if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
    diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
    index f9a81b187fae..a2c393385db0 100644
    --- a/security/integrity/evm/evm_main.c
    +++ b/security/integrity/evm/evm_main.c
    @@ -99,7 +99,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry)
    if (!(inode->i_opflags & IOP_XATTR))
    return -EOPNOTSUPP;

    - list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
    + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
    error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
    if (error < 0) {
    if (error == -ENODATA)
    @@ -230,7 +230,7 @@ static int evm_protected_xattr(const char *req_xattr_name)
    struct xattr_list *xattr;

    namelen = strlen(req_xattr_name);
    - list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
    + list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
    if ((strlen(xattr->name) == namelen)
    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
    found = 1;
    diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
    index c11c1f7b3ddd..0f37ef27268d 100644
    --- a/security/integrity/evm/evm_secfs.c
    +++ b/security/integrity/evm/evm_secfs.c
    @@ -234,7 +234,14 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
    goto out;
    }

    - /* Guard against races in evm_read_xattrs */
    + /*
    + * xattr_list_mutex guards against races in evm_read_xattrs().
    + * Entries are only added to the evm_config_xattrnames list
    + * and never deleted. Therefore, the list is traversed
    + * using list_for_each_entry_lockless() without holding
    + * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
    + * and evm_protected_xattr().
    + */
    mutex_lock(&xattr_list_mutex);
    list_for_each_entry(tmp, &evm_config_xattrnames, list) {
    if (strcmp(xattr->name, tmp->name) == 0) {
    --
    2.25.1
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