On 06/20/2014 01:45 PM, Waiman Long wrote:
> With 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 in security_genfs_sid() by adding a 5th argument to
> indicate if the rwlock has been taken.
>
> Signed-off-by: Waiman Long <waiman.l...@hp.com>
Thanks, but I'd prefer to instead create a static helper function in
services.c that does not take the lock at all, use that function from
security_fs_use, and leave the extern function unmodified.
> ---
> security/selinux/hooks.c | 2 +-
> security/selinux/include/security.h | 2 +-
> security/selinux/selinuxfs.c | 3 ++-
> security/selinux/ss/services.c | 13 +++++++++----
> 4 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 83d06db..430035a 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1248,7 +1248,7 @@ static int selinux_proc_get_sid(struct dentry *dentry,
> path[1] = '/';
> path++;
> }
> - rc = security_genfs_sid("proc", path, tclass, sid);
> + rc = security_genfs_sid("proc", path, tclass, sid, false);
> }
> free_page((unsigned long)buffer);
> return rc;
> diff --git a/security/selinux/include/security.h
> b/security/selinux/include/security.h
> index ce7852c..6bc5b2f 100644
> --- a/security/selinux/include/security.h
> +++ b/security/selinux/include/security.h
> @@ -180,7 +180,7 @@ int security_get_allow_unknown(void);
> int security_fs_use(struct super_block *sb);
>
> int security_genfs_sid(const char *fstype, char *name, u16 sclass,
> - u32 *sid);
> + u32 *sid, int locked);
>
> #ifdef CONFIG_NETLABEL
> int security_netlbl_secattr_to_sid(struct netlbl_lsm_secattr *secattr,
> diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> index c71737f..405799e 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -1273,7 +1273,8 @@ static int sel_make_bools(void)
> goto out;
>
> isec = (struct inode_security_struct *)inode->i_security;
> - ret = security_genfs_sid("selinuxfs", page, SECCLASS_FILE,
> &sid);
> + ret = security_genfs_sid("selinuxfs", page, SECCLASS_FILE,
> + &sid, false);
> if (ret)
> goto out;
>
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index 4bca494..2b23c2c 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2282,6 +2282,7 @@ out:
> * @path: path from root of mount
> * @sclass: file security class
> * @sid: SID for path
> + * @locked: true if policy_rwlock taken
> *
> * Obtain a SID to use for a file in a filesystem that
> * cannot support xattr or use a fixed labeling behavior like
> @@ -2290,7 +2291,8 @@ out:
> int security_genfs_sid(const char *fstype,
> char *path,
> u16 orig_sclass,
> - u32 *sid)
> + u32 *sid,
> + int locked)
> {
> int len;
> u16 sclass;
> @@ -2301,7 +2303,8 @@ int security_genfs_sid(const char *fstype,
> while (path[0] == '/' && path[1] == '/')
> path++;
>
> - read_lock(&policy_rwlock);
> + if (!locked)
> + read_lock(&policy_rwlock);
>
> sclass = unmap_class(orig_sclass);
> *sid = SECINITSID_UNLABELED;
> @@ -2336,7 +2339,8 @@ int security_genfs_sid(const char *fstype,
> *sid = c->sid[0];
> rc = 0;
> out:
> - read_unlock(&policy_rwlock);
> + if (!locked)
> + read_unlock(&policy_rwlock);
> return rc;
> }
>
> @@ -2370,7 +2374,8 @@ 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,
> + true);
> if (rc) {
> sbsec->behavior = SECURITY_FS_USE_NONE;
> rc = 0;
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
