[PATCH 6.6 004/158] smb: client: guarantee refcounted children from parent session

Greg Kroah-Hartman
2024-04-23T21:42:48Z

From: Paulo Alcantara <pc@manguebit.com>

[ Upstream commit 062a7f0ff46eb57aff526897bd2bebfdb1d3046a ]

Avoid potential use-after-free bugs when walking DFS referrals,
mounting and performing DFS failover by ensuring that all children
from parent @tcon->ses are also refcounted. They're all needed across
the entire DFS mount. Get rid of @tcon->dfs_ses_list while we're at
it, too.

Cc: stable@vger.kernel.org # 6.4+
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404021527.ZlRkIxgv-lkp@intel.com/
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/smb/client/cifsglob.h | 2 --
fs/smb/client/cifsproto.h | 20 +++++++--------
fs/smb/client/connect.c | 25 +++++++++++++++----
fs/smb/client/dfs.c | 51 ++++++++++++++++++---------------------
fs/smb/client/dfs.h | 33 ++++++++++++++++---------
fs/smb/client/dfs_cache.c | 11 +--------
fs/smb/client/misc.c | 6 -----
7 files changed, 76 insertions(+), 72 deletions(-)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 01d7031194671..68fd61a564089 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1253,7 +1253,6 @@ struct cifs_tcon {
struct cached_fids *cfids;
/* BB add field for back pointer to sb struct(s)? */
#ifdef CONFIG_CIFS_DFS_UPCALL
- struct list_head dfs_ses_list;
struct delayed_work dfs_cache_work;
#endif
struct delayed_work query_interfaces; /* query interfaces workqueue job */
@@ -1775,7 +1774,6 @@ struct cifs_mount_ctx {
struct TCP_Server_Info *server;
struct cifs_ses *ses;
struct cifs_tcon *tcon;
- struct list_head dfs_ses_list;
};

static inline void __free_dfs_info_param(struct dfs_info3_param *param)
diff --git a/fs/smb/client/cifsproto.h b/fs/smb/client/cifsproto.h
index ed257612bf0bc..1bdad33580b57 100644
--- a/fs/smb/client/cifsproto.h
+++ b/fs/smb/client/cifsproto.h
@@ -716,31 +716,31 @@ struct super_block *cifs_get_tcon_super(struct cifs_tcon *tcon);
void cifs_put_tcon_super(struct super_block *sb);
int cifs_wait_for_server_reconnect(struct TCP_Server_Info *server, bool retry);

-/* Put references of @ses and @ses->dfs_root_ses */
+/* Put references of @ses and its children */
static inline void cifs_put_smb_ses(struct cifs_ses *ses)
{
- struct cifs_ses *rses = ses->dfs_root_ses;
+ struct cifs_ses *next;

- __cifs_put_smb_ses(ses);
- if (rses)
- __cifs_put_smb_ses(rses);
+ do {
+ next = ses->dfs_root_ses;
+ __cifs_put_smb_ses(ses);
+ } while ((ses = next));
}

-/* Get an active reference of @ses and @ses->dfs_root_ses.
+/* Get an active reference of @ses and its children.
*
* NOTE: make sure to call this function when incrementing reference count of
* @ses to ensure that any DFS root session attached to it (@ses->dfs_root_ses)
* will also get its reference count incremented.
*
- * cifs_put_smb_ses() will put both references, so call it when you're done.
+ * cifs_put_smb_ses() will put all references, so call it when you're done.
*/
static inline void cifs_smb_ses_inc_refcount(struct cifs_ses *ses)
{
lockdep_assert_held(&cifs_tcp_ses_lock);

- ses->ses_count++;
- if (ses->dfs_root_ses)
- ses->dfs_root_ses->ses_count++;
+ for (; ses; ses = ses->dfs_root_ses)
+ ses->ses_count++;
}

static inline bool dfs_src_pathname_equal(const char *s1, const char *s2)
diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
index ae35855966afd..c5705de7f9de2 100644
--- a/fs/smb/client/connect.c
+++ b/fs/smb/client/connect.c
@@ -1863,6 +1863,9 @@ static int match_session(struct cifs_ses *ses, struct smb3_fs_context *ctx)
ctx->sectype != ses->sectype)
return 0;

+ if (ctx->dfs_root_ses != ses->dfs_root_ses)
+ return 0;
+
/*
* If an existing session is limited to less channels than
* requested, it should not be reused
@@ -2355,9 +2358,9 @@ cifs_get_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
* need to lock before changing something in the session.
*/
spin_lock(&cifs_tcp_ses_lock);
+ if (ctx->dfs_root_ses)
+ cifs_smb_ses_inc_refcount(ctx->dfs_root_ses);
ses->dfs_root_ses = ctx->dfs_root_ses;
- if (ses->dfs_root_ses)
- ses->dfs_root_ses->ses_count++;
list_add(&ses->smb_ses_list, &server->smb_ses_list);
spin_unlock(&cifs_tcp_ses_lock);

@@ -3301,6 +3304,9 @@ void cifs_mount_put_conns(struct cifs_mount_ctx *mnt_ctx)
cifs_put_smb_ses(mnt_ctx->ses);
else if (mnt_ctx->server)
cifs_put_tcp_session(mnt_ctx->server, 0);
+ mnt_ctx->ses = NULL;
+ mnt_ctx->tcon = NULL;
+ mnt_ctx->server = NULL;
mnt_ctx->cifs_sb->mnt_cifs_flags &= ~CIFS_MOUNT_POSIX_PATHS;
free_xid(mnt_ctx->xid);
}
@@ -3579,8 +3585,6 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
bool isdfs;
int rc;

- INIT_LIST_HEAD(&mnt_ctx.dfs_ses_list);
-
rc = dfs_mount_share(&mnt_ctx, &isdfs);
if (rc)
goto error;
@@ -3611,7 +3615,6 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
return rc;

error:
- dfs_put_root_smb_sessions(&mnt_ctx.dfs_ses_list);
cifs_mount_put_conns(&mnt_ctx);
return rc;
}
@@ -3626,6 +3629,18 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
goto error;

rc = cifs_mount_get_tcon(&mnt_ctx);
+ if (!rc) {
+ /*
+ * Prevent superblock from being created with any missing
+ * connections.
+ */
+ if (WARN_ON(!mnt_ctx.server))
+ rc = -EHOSTDOWN;
+ else if (WARN_ON(!mnt_ctx.ses))
+ rc = -EACCES;
+ else if (WARN_ON(!mnt_ctx.tcon))
+ rc = -ENOENT;
+ }
if (rc)
goto error;

diff --git a/fs/smb/client/dfs.c b/fs/smb/client/dfs.c
index 449c59830039b..3ec965547e3d4 100644
--- a/fs/smb/client/dfs.c
+++ b/fs/smb/client/dfs.c
@@ -66,33 +66,20 @@ static int get_session(struct cifs_mount_ctx *mnt_ctx, const char *full_path)
}

/*
- * Track individual DFS referral servers used by new DFS mount.
- *
- * On success, their lifetime will be shared by final tcon (dfs_ses_list).
- * Otherwise, they will be put by dfs_put_root_smb_sessions() in cifs_mount().
+ * Get an active reference of @ses so that next call to cifs_put_tcon() won't
+ * release it as any new DFS referrals must go through its IPC tcon.
*/
-static int add_root_smb_session(struct cifs_mount_ctx *mnt_ctx)
+static void add_root_smb_session(struct cifs_mount_ctx *mnt_ctx)
{
struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
- struct dfs_root_ses *root_ses;
struct cifs_ses *ses = mnt_ctx->ses;

if (ses) {
- root_ses = kmalloc(sizeof(*root_ses), GFP_KERNEL);
- if (!root_ses)
- return -ENOMEM;
-
- INIT_LIST_HEAD(&root_ses->list);
-
spin_lock(&cifs_tcp_ses_lock);
cifs_smb_ses_inc_refcount(ses);
spin_unlock(&cifs_tcp_ses_lock);
- root_ses->ses = ses;
- list_add_tail(&root_ses->list, &mnt_ctx->dfs_ses_list);
}
- /* Select new DFS referral server so that new referrals go through it */
ctx->dfs_root_ses = ses;
- return 0;
}

static inline int parse_dfs_target(struct smb3_fs_context *ctx,
@@ -185,11 +172,8 @@ static int __dfs_referral_walk(struct cifs_mount_ctx *mnt_ctx,
continue;
}

- if (is_refsrv) {
- rc = add_root_smb_session(mnt_ctx);
- if (rc)
- goto out;
- }
+ if (is_refsrv)
+ add_root_smb_session(mnt_ctx);

rc = ref_walk_advance(rw);
if (!rc) {
@@ -232,6 +216,7 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
struct cifs_tcon *tcon;
char *origin_fullpath;
+ bool new_tcon = true;
int rc;

origin_fullpath = dfs_get_path(cifs_sb, ctx->source);
@@ -239,6 +224,18 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
return PTR_ERR(origin_fullpath);

rc = dfs_referral_walk(mnt_ctx);
+ if (!rc) {
+ /*
+ * Prevent superblock from being created with any missing
+ * connections.
+ */
+ if (WARN_ON(!mnt_ctx->server))
+ rc = -EHOSTDOWN;
+ else if (WARN_ON(!mnt_ctx->ses))
+ rc = -EACCES;
+ else if (WARN_ON(!mnt_ctx->tcon))
+ rc = -ENOENT;
+ }
if (rc)
goto out;

@@ -247,15 +244,14 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
if (!tcon->origin_fullpath) {
tcon->origin_fullpath = origin_fullpath;
origin_fullpath = NULL;
+ } else {
+ new_tcon = false;
}
spin_unlock(&tcon->tc_lock);

- if (list_empty(&tcon->dfs_ses_list)) {
- list_replace_init(&mnt_ctx->dfs_ses_list, &tcon->dfs_ses_list);
+ if (new_tcon) {
queue_delayed_work(dfscache_wq, &tcon->dfs_cache_work,
dfs_cache_get_ttl() * HZ);
- } else {
- dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
}

out:
@@ -298,7 +294,6 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
if (rc)
return rc;

- ctx->dfs_root_ses = mnt_ctx->ses;
/*
* If called with 'nodfs' mount option, then skip DFS resolving. Otherwise unconditionally
* try to get an DFS referral (even cached) to determine whether it is an DFS mount.
@@ -324,7 +319,9 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)

*isdfs = true;
add_root_smb_session(mnt_ctx);
- return __dfs_mount_share(mnt_ctx);
+ rc = __dfs_mount_share(mnt_ctx);
+ dfs_put_root_smb_sessions(mnt_ctx);
+ return rc;
}

/* Update dfs referral path of superblock */
diff --git a/fs/smb/client/dfs.h b/fs/smb/client/dfs.h
index 875ab7ae57fcd..e5c4dcf837503 100644
--- a/fs/smb/client/dfs.h
+++ b/fs/smb/client/dfs.h
@@ -7,7 +7,9 @@
#define _CIFS_DFS_H

#include "cifsglob.h"
+#include "cifsproto.h"
#include "fs_context.h"
+#include "dfs_cache.h"
#include "cifs_unicode.h"
#include <linux/namei.h>

@@ -114,11 +116,6 @@ static inline void ref_walk_set_tgt_hint(struct dfs_ref_walk *rw)
ref_walk_tit(rw));
}

-struct dfs_root_ses {
- struct list_head list;
- struct cifs_ses *ses;
-};
-
int dfs_parse_target_referral(const char *full_path, const struct dfs_info3_param *ref,
struct smb3_fs_context *ctx);
int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs);
@@ -133,20 +130,32 @@ static inline int dfs_get_referral(struct cifs_mount_ctx *mnt_ctx, const char *p
{
struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
struct cifs_sb_info *cifs_sb = mnt_ctx->cifs_sb;
+ struct cifs_ses *rses = ctx->dfs_root_ses ?: mnt_ctx->ses;

- return dfs_cache_find(mnt_ctx->xid, ctx->dfs_root_ses, cifs_sb->local_nls,
+ return dfs_cache_find(mnt_ctx->xid, rses, cifs_sb->local_nls,
cifs_remap(cifs_sb), path, ref, tl);
}

-static inline void dfs_put_root_smb_sessions(struct list_head *head)
+/*
+ * cifs_get_smb_ses() already guarantees an active reference of
+ * @ses->dfs_root_ses when a new session is created, so we need to put extra
+ * references of all DFS root sessions that were used across the mount process
+ * in dfs_mount_share().
+ */
+static inline void dfs_put_root_smb_sessions(struct cifs_mount_ctx *mnt_ctx)
{
- struct dfs_root_ses *root, *tmp;
+ const struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
+ struct cifs_ses *ses = ctx->dfs_root_ses;
+ struct cifs_ses *cur;
+
+ if (!ses)
+ return;

- list_for_each_entry_safe(root, tmp, head, list) {
- list_del_init(&root->list);
- cifs_put_smb_ses(root->ses);
- kfree(root);
+ for (cur = ses; cur; cur = cur->dfs_root_ses) {
+ if (cur->dfs_root_ses)
+ cifs_put_smb_ses(cur->dfs_root_ses);
}
+ cifs_put_smb_ses(ses);
}

#endif /* _CIFS_DFS_H */
diff --git a/fs/smb/client/dfs_cache.c b/fs/smb/client/dfs_cache.c
index 508d831fabe37..0552a864ff08f 100644
--- a/fs/smb/client/dfs_cache.c
+++ b/fs/smb/client/dfs_cache.c
@@ -1278,21 +1278,12 @@ int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb)
void dfs_cache_refresh(struct work_struct *work)
{
struct TCP_Server_Info *server;
- struct dfs_root_ses *rses;
struct cifs_tcon *tcon;
struct cifs_ses *ses;

tcon = container_of(work, struct cifs_tcon, dfs_cache_work.work);
- ses = tcon->ses;
- server = ses->server;

- mutex_lock(&server->refpath_lock);
- if (server->leaf_fullpath)
- __refresh_tcon(server->leaf_fullpath + 1, ses, false);
- mutex_unlock(&server->refpath_lock);
-
- list_for_each_entry(rses, &tcon->dfs_ses_list, list) {
- ses = rses->ses;
+ for (ses = tcon->ses; ses; ses = ses->dfs_root_ses) {
server = ses->server;
mutex_lock(&server->refpath_lock);
if (server->leaf_fullpath)
diff --git a/fs/smb/client/misc.c b/fs/smb/client/misc.c
index 51413cb00e199..74627d647818a 100644
--- a/fs/smb/client/misc.c
+++ b/fs/smb/client/misc.c
@@ -141,9 +141,6 @@ tcon_info_alloc(bool dir_leases_enabled)
atomic_set(&ret_buf->num_local_opens, 0);
atomic_set(&ret_buf->num_remote_opens, 0);
ret_buf->stats_from_time = ktime_get_real_seconds();
-#ifdef CONFIG_CIFS_DFS_UPCALL
- INIT_LIST_HEAD(&ret_buf->dfs_ses_list);
-#endif

return ret_buf;
}
@@ -159,9 +156,6 @@ tconInfoFree(struct cifs_tcon *tcon)
atomic_dec(&tconInfoAllocCount);
kfree(tcon->nativeFileSystem);
kfree_sensitive(tcon->password);
-#ifdef CONFIG_CIFS_DFS_UPCALL
- dfs_put_root_smb_sessions(&tcon->dfs_ses_list);
-#endif
kfree(tcon->origin_fullpath);
kfree(tcon);
}
--
2.43.0