ceph: fix potential use-after-free bug when trimming caps

When trimming the caps and just after the 'session->s_cap_lock' is
released in ceph_iterate_session_caps() the cap maybe removed by
another thread, and when using the stale cap memory in the callbacks
it will trigger use-after-free crash.

We need to check the existence of the cap just after the 'ci->i_ceph_lock'
being acquired. And do nothing if it's already removed.

Cc: stable@vger.kernel.org
Link: https://tracker.ceph.com/issues/43272
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Luís Henriques <lhenriques@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 7cc2077..789be30 100644 (file)
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -431,7 +431,7 @@ void ceph_reservation_status(struct ceph_fs_client *fsc,
  *
  * Called with i_ceph_lock held.
  */
-static struct ceph_cap *__get_cap_for_mds(struct ceph_inode_info *ci, int mds)
+struct ceph_cap *__get_cap_for_mds(struct ceph_inode_info *ci, int mds)
 {
        struct ceph_cap *cap;
        struct rb_node *n = ci->i_caps.rb_node;

diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index bec3c45..3904333 100644 (file)
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -248,14 +248,20 @@ static int metrics_caps_show(struct seq_file *s, void *p)
        return 0;
 }
 
-static int caps_show_cb(struct inode *inode, struct ceph_cap *cap, void *p)
+static int caps_show_cb(struct inode *inode, int mds, void *p)
 {
+       struct ceph_inode_info *ci = ceph_inode(inode);
        struct seq_file *s = p;
-
-       seq_printf(s, "0x%-17llx%-3d%-17s%-17s\n", ceph_ino(inode),
-                  cap->session->s_mds,
-                  ceph_cap_string(cap->issued),
-                  ceph_cap_string(cap->implemented));
+       struct ceph_cap *cap;
+
+       spin_lock(&ci->i_ceph_lock);
+       cap = __get_cap_for_mds(ci, mds);
+       if (cap)
+               seq_printf(s, "0x%-17llx%-3d%-17s%-17s\n", ceph_ino(inode),
+                          cap->session->s_mds,
+                          ceph_cap_string(cap->issued),
+                          ceph_cap_string(cap->implemented));
+       spin_unlock(&ci->i_ceph_lock);
        return 0;
 }
 

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 27a245d..54e3c2a 100644 (file)
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -1632,8 +1632,8 @@ static void cleanup_session_requests(struct ceph_mds_client *mdsc,
  * Caller must hold session s_mutex.
  */
 int ceph_iterate_session_caps(struct ceph_mds_session *session,
-                             int (*cb)(struct inode *, struct ceph_cap *,
-                                       void *), void *arg)
+                             int (*cb)(struct inode *, int mds, void *),
+                             void *arg)
 {
        struct list_head *p;
        struct ceph_cap *cap;
@@ -1645,6 +1645,8 @@ int ceph_iterate_session_caps(struct ceph_mds_session *session,
        spin_lock(&session->s_cap_lock);
        p = session->s_caps.next;
        while (p != &session->s_caps) {
+               int mds;
+
                cap = list_entry(p, struct ceph_cap, session_caps);
                inode = igrab(&cap->ci->netfs.inode);
                if (!inode) {
@@ -1652,6 +1654,7 @@ int ceph_iterate_session_caps(struct ceph_mds_session *session,
                        continue;
                }
                session->s_cap_iterator = cap;
+               mds = cap->mds;
                spin_unlock(&session->s_cap_lock);
 
                if (last_inode) {
@@ -1663,7 +1666,7 @@ int ceph_iterate_session_caps(struct ceph_mds_session *session,
                        old_cap = NULL;
                }
 
-               ret = cb(inode, cap, arg);
+               ret = cb(inode, mds, arg);
                last_inode = inode;
 
                spin_lock(&session->s_cap_lock);
@@ -1696,20 +1699,25 @@ out:
        return ret;
 }
 
-static int remove_session_caps_cb(struct inode *inode, struct ceph_cap *cap,
-                                 void *arg)
+static int remove_session_caps_cb(struct inode *inode, int mds, void *arg)
 {
        struct ceph_inode_info *ci = ceph_inode(inode);
        bool invalidate = false;
-       int iputs;
+       struct ceph_cap *cap;
+       int iputs = 0;
 
-       dout("removing cap %p, ci is %p, inode is %p\n",
-            cap, ci, &ci->netfs.inode);
        spin_lock(&ci->i_ceph_lock);
-       iputs = ceph_purge_inode_cap(inode, cap, &invalidate);
+       cap = __get_cap_for_mds(ci, mds);
+       if (cap) {
+               dout(" removing cap %p, ci is %p, inode is %p\n",
+                    cap, ci, &ci->netfs.inode);
+
+               iputs = ceph_purge_inode_cap(inode, cap, &invalidate);
+       }
        spin_unlock(&ci->i_ceph_lock);
 
-       wake_up_all(&ci->i_cap_wq);
+       if (cap)
+               wake_up_all(&ci->i_cap_wq);
        if (invalidate)
                ceph_queue_invalidate(inode);
        while (iputs--)
@@ -1780,8 +1788,7 @@ enum {
  *
  * caller must hold s_mutex.
  */
-static int wake_up_session_cb(struct inode *inode, struct ceph_cap *cap,
-                             void *arg)
+static int wake_up_session_cb(struct inode *inode, int mds, void *arg)
 {
        struct ceph_inode_info *ci = ceph_inode(inode);
        unsigned long ev = (unsigned long)arg;
@@ -1792,12 +1799,14 @@ static int wake_up_session_cb(struct inode *inode, struct ceph_cap *cap,
                ci->i_requested_max_size = 0;
                spin_unlock(&ci->i_ceph_lock);
        } else if (ev == RENEWCAPS) {
-               if (cap->cap_gen < atomic_read(&cap->session->s_cap_gen)) {
-                       /* mds did not re-issue stale cap */
-                       spin_lock(&ci->i_ceph_lock);
+               struct ceph_cap *cap;
+
+               spin_lock(&ci->i_ceph_lock);
+               cap = __get_cap_for_mds(ci, mds);
+               /* mds did not re-issue stale cap */
+               if (cap && cap->cap_gen < atomic_read(&cap->session->s_cap_gen))
                        cap->issued = cap->implemented = CEPH_CAP_PIN;
-                       spin_unlock(&ci->i_ceph_lock);
-               }
+               spin_unlock(&ci->i_ceph_lock);
        } else if (ev == FORCE_RO) {
        }
        wake_up_all(&ci->i_cap_wq);
@@ -1959,16 +1968,22 @@ out:
  * Yes, this is a bit sloppy.  Our only real goal here is to respond to
  * memory pressure from the MDS, though, so it needn't be perfect.
  */
-static int trim_caps_cb(struct inode *inode, struct ceph_cap *cap, void *arg)
+static int trim_caps_cb(struct inode *inode, int mds, void *arg)
 {
        int *remaining = arg;
        struct ceph_inode_info *ci = ceph_inode(inode);
        int used, wanted, oissued, mine;
+       struct ceph_cap *cap;
 
        if (*remaining <= 0)
                return -1;
 
        spin_lock(&ci->i_ceph_lock);
+       cap = __get_cap_for_mds(ci, mds);
+       if (!cap) {
+               spin_unlock(&ci->i_ceph_lock);
+               return 0;
+       }
        mine = cap->issued | cap->implemented;
        used = __ceph_caps_used(ci);
        wanted = __ceph_caps_file_wanted(ci);
@@ -3911,26 +3926,22 @@ out_unlock:
 /*
  * Encode information about a cap for a reconnect with the MDS.
  */
-static int reconnect_caps_cb(struct inode *inode, struct ceph_cap *cap,
-                         void *arg)
+static int reconnect_caps_cb(struct inode *inode, int mds, void *arg)
 {
        union {
                struct ceph_mds_cap_reconnect v2;
                struct ceph_mds_cap_reconnect_v1 v1;
        } rec;
-       struct ceph_inode_info *ci = cap->ci;
+       struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_reconnect_state *recon_state = arg;
        struct ceph_pagelist *pagelist = recon_state->pagelist;
        struct dentry *dentry;
+       struct ceph_cap *cap;
        char *path;
-       int pathlen = 0, err;
+       int pathlen = 0, err = 0;
        u64 pathbase;
        u64 snap_follows;
 
-       dout(" adding %p ino %llx.%llx cap %p %lld %s\n",
-            inode, ceph_vinop(inode), cap, cap->cap_id,
-            ceph_cap_string(cap->issued));
-
        dentry = d_find_primary(inode);
        if (dentry) {
                /* set pathbase to parent dir when msg_version >= 2 */
@@ -3947,6 +3958,15 @@ static int reconnect_caps_cb(struct inode *inode, struct ceph_cap *cap,
        }
 
        spin_lock(&ci->i_ceph_lock);
+       cap = __get_cap_for_mds(ci, mds);
+       if (!cap) {
+               spin_unlock(&ci->i_ceph_lock);
+               goto out_err;
+       }
+       dout(" adding %p ino %llx.%llx cap %p %lld %s\n",
+            inode, ceph_vinop(inode), cap, cap->cap_id,
+            ceph_cap_string(cap->issued));
+
        cap->seq = 0;        /* reset cap seq */
        cap->issue_seq = 0;  /* and issue_seq */
        cap->mseq = 0;       /* and migrate_seq */

diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 0598faa..18b026b 100644 (file)
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -541,8 +541,7 @@ extern void ceph_flush_cap_releases(struct ceph_mds_client *mdsc,
 extern void ceph_queue_cap_reclaim_work(struct ceph_mds_client *mdsc);
 extern void ceph_reclaim_caps_nr(struct ceph_mds_client *mdsc, int nr);
 extern int ceph_iterate_session_caps(struct ceph_mds_session *session,
-                                    int (*cb)(struct inode *,
-                                              struct ceph_cap *, void *),
+                                    int (*cb)(struct inode *, int mds, void *),
                                     void *arg);
 extern void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc);
 

diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 6ecca2c..d24bf0d 100644 (file)
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -1192,6 +1192,8 @@ extern void ceph_kick_flushing_caps(struct ceph_mds_client *mdsc,
                                    struct ceph_mds_session *session);
 void ceph_kick_flushing_inode_caps(struct ceph_mds_session *session,
                                   struct ceph_inode_info *ci);
+extern struct ceph_cap *__get_cap_for_mds(struct ceph_inode_info *ci,
+                                         int mds);
 extern struct ceph_cap *ceph_get_cap_for_mds(struct ceph_inode_info *ci,
                                             int mds);
 extern void ceph_take_cap_refs(struct ceph_inode_info *ci, int caps,