With the introduction of fair queued rwlock, recursive read_lock()
may hang the offending process if there is a write_lock() somewhere
in between.
With recursive read_lock checking enabled, the following error was
reported:
=============================================
[ INFO: possible recursive locking detected ]
3.16.0-rc1 #2 Tainted: G E
---------------------------------------------
load_policy/708 is trying to acquire lock:
(policy_rwlock){.+.+..}, at: [<ffffffff8125b32a>]
security_genfs_sid+0x3a/0x170
but task is already holding lock:
(policy_rwlock){.+.+..}, at: [<ffffffff8125b48c>]
security_fs_use+0x2c/0x110
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(policy_rwlock);
lock(policy_rwlock);
This patch fixes the occurrence of recursive read_lock() of
policy_rwlock by adding a helper function __security_genfs_sid()
which requires caller to take the lock before calling it. The
security_fs_use() was then modified to call the new helper function.
Signed-off-by: Waiman Long <[email protected]>
---
security/selinux/ss/services.c | 41 +++++++++++++++++++++++++++++++--------
1 files changed, 32 insertions(+), 9 deletions(-)
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 4bca494..2aa9d17 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -2277,7 +2277,7 @@ out:
}
/**
- * security_genfs_sid - Obtain a SID for a file in a filesystem
+ * __security_genfs_sid - Helper to obtain a SID for a file in a filesystem
* @fstype: filesystem type
* @path: path from root of mount
* @sclass: file security class
@@ -2286,11 +2286,13 @@ out:
* Obtain a SID to use for a file in a filesystem that
* cannot support xattr or use a fixed labeling behavior like
* transition SIDs or task SIDs.
+ *
+ * The caller must acquire the policy_rwlock before calling this function.
*/
-int security_genfs_sid(const char *fstype,
- char *path,
- u16 orig_sclass,
- u32 *sid)
+static inline int __security_genfs_sid(const char *fstype,
+ char *path,
+ u16 orig_sclass,
+ u32 *sid)
{
int len;
u16 sclass;
@@ -2301,8 +2303,6 @@ int security_genfs_sid(const char *fstype,
while (path[0] == '/' && path[1] == '/')
path++;
- read_lock(&policy_rwlock);
-
sclass = unmap_class(orig_sclass);
*sid = SECINITSID_UNLABELED;
@@ -2336,11 +2336,33 @@ int security_genfs_sid(const char *fstype,
*sid = c->sid[0];
rc = 0;
out:
- read_unlock(&policy_rwlock);
return rc;
}
/**
+ * security_genfs_sid - Obtain a SID for a file in a filesystem
+ * @fstype: filesystem type
+ * @path: path from root of mount
+ * @sclass: file security class
+ * @sid: SID for path
+ *
+ * Acquire policy_rwlock before calling __security_genfs_sid() and release
+ * it afterward.
+ */
+int security_genfs_sid(const char *fstype,
+ char *path,
+ u16 orig_sclass,
+ u32 *sid)
+{
+ int retval;
+
+ read_lock(&policy_rwlock);
+ retval = __security_genfs_sid(fstype, path, orig_sclass, sid);
+ read_unlock(&policy_rwlock);
+ return retval;
+}
+
+/**
* security_fs_use - Determine how to handle labeling for a filesystem.
* @sb: superblock in question
*/
@@ -2370,7 +2392,8 @@ int security_fs_use(struct super_block *sb)
}
sbsec->sid = c->sid[0];
} else {
- rc = security_genfs_sid(fstype, "/", SECCLASS_DIR, &sbsec->sid);
+ rc = __security_genfs_sid(fstype, "/", SECCLASS_DIR,
+ &sbsec->sid);
if (rc) {
sbsec->behavior = SECURITY_FS_USE_NONE;
rc = 0;
--
1.7.1
On 06/23/2014 11:28 AM, Waiman Long wrote:
> With the introduction of fair queued rwlock, recursive read_lock()
> may hang the offending process if there is a write_lock() somewhere
> in between.
>
> With recursive read_lock checking enabled, the following error was
> reported:
>
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.16.0-rc1 #2 Tainted: G E
> ---------------------------------------------
> load_policy/708 is trying to acquire lock:
> (policy_rwlock){.+.+..}, at: [<ffffffff8125b32a>]
> security_genfs_sid+0x3a/0x170
>
> but task is already holding lock:
> (policy_rwlock){.+.+..}, at: [<ffffffff8125b48c>]
> security_fs_use+0x2c/0x110
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(policy_rwlock);
> lock(policy_rwlock);
>
> This patch fixes the occurrence of recursive read_lock() of
> policy_rwlock by adding a helper function __security_genfs_sid()
> which requires caller to take the lock before calling it. The
> security_fs_use() was then modified to call the new helper function.
>
> Signed-off-by: Waiman Long <[email protected]>
Acked-by: Stephen Smalley <[email protected]>
> ---
> security/selinux/ss/services.c | 41 +++++++++++++++++++++++++++++++--------
> 1 files changed, 32 insertions(+), 9 deletions(-)
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 4bca494..2aa9d17 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2277,7 +2277,7 @@ out:
> }
>
> /**
> - * security_genfs_sid - Obtain a SID for a file in a filesystem
> + * __security_genfs_sid - Helper to obtain a SID for a file in a filesystem
> * @fstype: filesystem type
> * @path: path from root of mount
> * @sclass: file security class
> @@ -2286,11 +2286,13 @@ out:
> * Obtain a SID to use for a file in a filesystem that
> * cannot support xattr or use a fixed labeling behavior like
> * transition SIDs or task SIDs.
> + *
> + * The caller must acquire the policy_rwlock before calling this function.
> */
> -int security_genfs_sid(const char *fstype,
> - char *path,
> - u16 orig_sclass,
> - u32 *sid)
> +static inline int __security_genfs_sid(const char *fstype,
> + char *path,
> + u16 orig_sclass,
> + u32 *sid)
> {
> int len;
> u16 sclass;
> @@ -2301,8 +2303,6 @@ int security_genfs_sid(const char *fstype,
> while (path[0] == '/' && path[1] == '/')
> path++;
>
> - read_lock(&policy_rwlock);
> -
> sclass = unmap_class(orig_sclass);
> *sid = SECINITSID_UNLABELED;
>
> @@ -2336,11 +2336,33 @@ int security_genfs_sid(const char *fstype,
> *sid = c->sid[0];
> rc = 0;
> out:
> - read_unlock(&policy_rwlock);
> return rc;
> }
>
> /**
> + * security_genfs_sid - Obtain a SID for a file in a filesystem
> + * @fstype: filesystem type
> + * @path: path from root of mount
> + * @sclass: file security class
> + * @sid: SID for path
> + *
> + * Acquire policy_rwlock before calling __security_genfs_sid() and release
> + * it afterward.
> + */
> +int security_genfs_sid(const char *fstype,
> + char *path,
> + u16 orig_sclass,
> + u32 *sid)
> +{
> + int retval;
> +
> + read_lock(&policy_rwlock);
> + retval = __security_genfs_sid(fstype, path, orig_sclass, sid);
> + read_unlock(&policy_rwlock);
> + return retval;
> +}
> +
> +/**
> * security_fs_use - Determine how to handle labeling for a filesystem.
> * @sb: superblock in question
> */
> @@ -2370,7 +2392,8 @@ int security_fs_use(struct super_block *sb)
> }
> sbsec->sid = c->sid[0];
> } else {
> - rc = security_genfs_sid(fstype, "/", SECCLASS_DIR, &sbsec->sid);
> + rc = __security_genfs_sid(fstype, "/", SECCLASS_DIR,
> + &sbsec->sid);
> if (rc) {
> sbsec->behavior = SECURITY_FS_USE_NONE;
> rc = 0;
>
On Monday, June 23, 2014 11:28:51 AM Waiman Long wrote:
> With the introduction of fair queued rwlock, recursive read_lock()
> may hang the offending process if there is a write_lock() somewhere
> in between.
>
> With recursive read_lock checking enabled, the following error was
> reported:
>
> =============================================
> [ INFO: possible recursive locking detected ]
> 3.16.0-rc1 #2 Tainted: G E
> ---------------------------------------------
> load_policy/708 is trying to acquire lock:
> (policy_rwlock){.+.+..}, at: [<ffffffff8125b32a>]
> security_genfs_sid+0x3a/0x170
>
> but task is already holding lock:
> (policy_rwlock){.+.+..}, at: [<ffffffff8125b48c>]
> security_fs_use+0x2c/0x110
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(policy_rwlock);
> lock(policy_rwlock);
>
> This patch fixes the occurrence of recursive read_lock() of
> policy_rwlock by adding a helper function __security_genfs_sid()
> which requires caller to take the lock before calling it. The
> security_fs_use() was then modified to call the new helper function.
>
> Signed-off-by: Waiman Long <[email protected]>
Applied, thank you.
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 4bca494..2aa9d17 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2277,7 +2277,7 @@ out:
> }
>
> /**
> - * security_genfs_sid - Obtain a SID for a file in a filesystem
> + * __security_genfs_sid - Helper to obtain a SID for a file in a filesystem
> * @fstype: filesystem type
> * @path: path from root of mount
> * @sclass: file security class
> @@ -2286,11 +2286,13 @@ out:
> * Obtain a SID to use for a file in a filesystem that
> * cannot support xattr or use a fixed labeling behavior like
> * transition SIDs or task SIDs.
> + *
> + * The caller must acquire the policy_rwlock before calling this function.
> */
> -int security_genfs_sid(const char *fstype,
> - char *path,
> - u16 orig_sclass,
> - u32 *sid)
> +static inline int __security_genfs_sid(const char *fstype,
> + char *path,
> + u16 orig_sclass,
> + u32 *sid)
> {
> int len;
> u16 sclass;
> @@ -2301,8 +2303,6 @@ int security_genfs_sid(const char *fstype,
> while (path[0] == '/' && path[1] == '/')
> path++;
>
> - read_lock(&policy_rwlock);
> -
> sclass = unmap_class(orig_sclass);
> *sid = SECINITSID_UNLABELED;
>
> @@ -2336,11 +2336,33 @@ int security_genfs_sid(const char *fstype,
> *sid = c->sid[0];
> rc = 0;
> out:
> - read_unlock(&policy_rwlock);
> return rc;
> }
>
> /**
> + * security_genfs_sid - Obtain a SID for a file in a filesystem
> + * @fstype: filesystem type
> + * @path: path from root of mount
> + * @sclass: file security class
> + * @sid: SID for path
> + *
> + * Acquire policy_rwlock before calling __security_genfs_sid() and release
> + * it afterward.
> + */
> +int security_genfs_sid(const char *fstype,
> + char *path,
> + u16 orig_sclass,
> + u32 *sid)
> +{
> + int retval;
> +
> + read_lock(&policy_rwlock);
> + retval = __security_genfs_sid(fstype, path, orig_sclass, sid);
> + read_unlock(&policy_rwlock);
> + return retval;
> +}
> +
> +/**
> * security_fs_use - Determine how to handle labeling for a filesystem.
> * @sb: superblock in question
> */
> @@ -2370,7 +2392,8 @@ int security_fs_use(struct super_block *sb)
> }
> sbsec->sid = c->sid[0];
> } else {
> - rc = security_genfs_sid(fstype, "/", SECCLASS_DIR, &sbsec->sid);
> + rc = __security_genfs_sid(fstype, "/", SECCLASS_DIR,
> + &sbsec->sid);
> if (rc) {
> sbsec->behavior = SECURITY_FS_USE_NONE;
> rc = 0;
--
paul moore
http://www.paul-moore.com