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
www.paul-moore.com
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