| Message ID | 20211206071859.324729-1-bernard@vivo.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | [v2] security/selinux: fix potential memleak in error branch | expand |
On Mon, Dec 6, 2021 at 8:19 AM Bernard Zhao <bernard@vivo.com> wrote: > This patch try to fix potential memleak in error branch. > > Signed-off-by: Bernard Zhao <bernard@vivo.com> > --- > security/selinux/hooks.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 62d30c0a30c2..8dc140399a23 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -983,18 +983,22 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, > static int selinux_add_opt(int token, const char *s, void **mnt_opts) > { > struct selinux_mnt_opts *opts = *mnt_opts; > + bool is_alloc_opts = false; > > if (token == Opt_seclabel) /* eaten and completely ignored */ > return 0; > > + if (!s) > + return -ENOMEM; > + > if (!opts) { > opts = kzalloc(sizeof(struct selinux_mnt_opts), GFP_KERNEL); > if (!opts) > return -ENOMEM; > *mnt_opts = opts; > + is_alloc_opts = true; > } > - if (!s) > - return -ENOMEM; > + > switch (token) { > case Opt_context: > if (opts->context || opts->defcontext) > @@ -1019,6 +1023,8 @@ static int selinux_add_opt(int token, const char *s, void **mnt_opts) > } > return 0; > Einval: > + if (is_alloc_opts) > + kfree(opts); > pr_warn(SEL_MOUNT_FAIL_MSG); > return -EINVAL; > } > -- > 2.33.1 The problem is a bit more tricky... As is, this patch will lead to double frees in some cases. Look at security_sb_eat_lsm_opts() callers, for example - some of them don't do anything when error is returned, some call security_free_mnt_opts() on the opts regardless, some will let it store the opts in fc->security, where put_fs_context() will eventually call security_free_mnt_opts() on them. You need to at least *mnt_opts = NULL after kfree(opts), but it would be also nice to make the LSM hook callers more consistent in what they do in the error path and document the fact that *mnt_opts will be NULL on error in lsm_hooks.h (in case of the sb_eat_lsm_opts hook).
-----邮件原件----- 发件人: bernard@vivo.com <bernard@vivo.com> 代表 Ondrej Mosnacek 发送时间: 2021年12月6日 17:11 收件人: 赵军奎 <bernard@vivo.com> 抄送: Paul Moore <paul@paul-moore.com>; Stephen Smalley <stephen.smalley.work@gmail.com>; Eric Paris <eparis@parisplace.org>; SElinux list <selinux@vger.kernel.org>; Linux kernel mailing list <linux-kernel@vger.kernel.org> 主题: Re: [PATCH v2] security/selinux: fix potential memleak in error branch On Mon, Dec 6, 2021 at 8:19 AM Bernard Zhao <bernard@vivo.com> wrote: > This patch try to fix potential memleak in error branch. > > Signed-off-by: Bernard Zhao <bernard@vivo.com> > --- > security/selinux/hooks.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index > 62d30c0a30c2..8dc140399a23 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -983,18 +983,22 @@ static int selinux_sb_clone_mnt_opts(const > struct super_block *oldsb, static int selinux_add_opt(int token, > const char *s, void **mnt_opts) { > struct selinux_mnt_opts *opts = *mnt_opts; > + bool is_alloc_opts = false; > > if (token == Opt_seclabel) /* eaten and completely ignored */ > return 0; > > + if (!s) > + return -ENOMEM; > + > if (!opts) { > opts = kzalloc(sizeof(struct selinux_mnt_opts), GFP_KERNEL); > if (!opts) > return -ENOMEM; > *mnt_opts = opts; > + is_alloc_opts = true; > } > - if (!s) > - return -ENOMEM; > + > switch (token) { > case Opt_context: > if (opts->context || opts->defcontext) @@ -1019,6 > +1023,8 @@ static int selinux_add_opt(int token, const char *s, void **mnt_opts) > } > return 0; > Einval: > + if (is_alloc_opts) > + kfree(opts); > pr_warn(SEL_MOUNT_FAIL_MSG); > return -EINVAL; > } > -- > 2.33.1 >The problem is a bit more tricky... As is, this patch will lead to double frees in some cases. Look at security_sb_eat_lsm_opts() callers, for example - some of them don't do anything when error is returned, some call >security_free_mnt_opts() on the opts regardless, some will let it store the opts in fc->security, where >put_fs_context() will eventually call security_free_mnt_opts() on them. >You need to at least *mnt_opts = NULL after kfree(opts), but it would be also nice to make the LSM hook callers more consistent in what they do in the error path and document the fact that *mnt_opts will be NULL >on error in lsm_hooks.h (in case of the sb_eat_lsm_opts hook). Hi Ondrej Mosnacek: Thanks for your comments! I am not sure if there is some gap, for this part " it would be also nice to make the LSM hook callers more consistent in what they do in the error path and document the fact that *mnt_opts will be NULL on error in lsm_hooks.h (in case of the sb_eat_lsm_opts hook)" I am not sure if this is OK: 116 * @sb_eat_lsm_opts: 117 * Eat (scan @orig options) and save them in @mnt_opts. 118 * If error is returned, then the *mnt_opts will be NULL. Please help to double check, thanks! BR//Bernard -- >Ondrej Mosnacek >Software Engineer, Linux Security - SELinux kernel Red Hat, Inc.
On Tue, Dec 7, 2021 at 1:05 PM 赵军奎 <bernard@vivo.com> wrote: > -----邮件原件----- > 发件人: bernard@vivo.com <bernard@vivo.com> 代表 Ondrej Mosnacek > 发送时间: 2021年12月6日 17:11 > 收件人: 赵军奎 <bernard@vivo.com> > 抄送: Paul Moore <paul@paul-moore.com>; Stephen Smalley <stephen.smalley.work@gmail.com>; Eric Paris <eparis@parisplace.org>; SElinux list <selinux@vger.kernel.org>; Linux kernel mailing list <linux-kernel@vger.kernel.org> > 主题: Re: [PATCH v2] security/selinux: fix potential memleak in error branch > > On Mon, Dec 6, 2021 at 8:19 AM Bernard Zhao <bernard@vivo.com> wrote: > > This patch try to fix potential memleak in error branch. > > > > Signed-off-by: Bernard Zhao <bernard@vivo.com> > > --- > > security/selinux/hooks.c | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index > > 62d30c0a30c2..8dc140399a23 100644 > > --- a/security/selinux/hooks.c > > +++ b/security/selinux/hooks.c > > @@ -983,18 +983,22 @@ static int selinux_sb_clone_mnt_opts(const > > struct super_block *oldsb, static int selinux_add_opt(int token, > > const char *s, void **mnt_opts) { > > struct selinux_mnt_opts *opts = *mnt_opts; > > + bool is_alloc_opts = false; > > > > if (token == Opt_seclabel) /* eaten and completely ignored */ > > return 0; > > > > + if (!s) > > + return -ENOMEM; > > + > > if (!opts) { > > opts = kzalloc(sizeof(struct selinux_mnt_opts), GFP_KERNEL); > > if (!opts) > > return -ENOMEM; > > *mnt_opts = opts; > > + is_alloc_opts = true; > > } > > - if (!s) > > - return -ENOMEM; > > + > > switch (token) { > > case Opt_context: > > if (opts->context || opts->defcontext) @@ -1019,6 > > +1023,8 @@ static int selinux_add_opt(int token, const char *s, void **mnt_opts) > > } > > return 0; > > Einval: > > + if (is_alloc_opts) > > + kfree(opts); > > pr_warn(SEL_MOUNT_FAIL_MSG); > > return -EINVAL; > > } > > -- > > 2.33.1 > > >The problem is a bit more tricky... As is, this patch will lead to double frees in some cases. Look at security_sb_eat_lsm_opts() callers, for example - some of them don't do anything when error is returned, some call > >security_free_mnt_opts() on the opts regardless, some will let it store the opts in fc->security, where > >put_fs_context() will eventually call security_free_mnt_opts() on them. > > >You need to at least *mnt_opts = NULL after kfree(opts), but it would be also nice to make the LSM hook callers more consistent in what they do in the error path and document the fact that *mnt_opts will be NULL > >on error in lsm_hooks.h (in case of the sb_eat_lsm_opts hook). > Hi Ondrej Mosnacek: > > Thanks for your comments! > I am not sure if there is some gap, for this part " it would be also nice to make the LSM hook callers more consistent in what they do in the error path and document the fact that *mnt_opts will be NULL > on error in lsm_hooks.h (in case of the sb_eat_lsm_opts hook)" > I am not sure if this is OK: > 116 * @sb_eat_lsm_opts: > 117 * Eat (scan @orig options) and save them in @mnt_opts. > 118 * If error is returned, then the *mnt_opts will be NULL. > Please help to double check, thanks! I'd prefer something like: If the hook returns 0, the caller is responsible for destroying the returned @mnt_opts using the @sb_free_mnt_opts hook. The LSMs must not expect the callers to destroy @mnt_opts if the hook returns an error and should always set it to NULL in such case. (You may want to double-check that the other implementations of this hook (i.e. security/smack/smack_lsm.c) follow that contract and fix them if necessary.) Thanks for your efforts to improve this! -- Ondrej Mosnacek Software Engineer, Linux Security - SELinux kernel Red Hat, Inc.
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 62d30c0a30c2..8dc140399a23 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -983,18 +983,22 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, static int selinux_add_opt(int token, const char *s, void **mnt_opts) { struct selinux_mnt_opts *opts = *mnt_opts; + bool is_alloc_opts = false; if (token == Opt_seclabel) /* eaten and completely ignored */ return 0; + if (!s) + return -ENOMEM; + if (!opts) { opts = kzalloc(sizeof(struct selinux_mnt_opts), GFP_KERNEL); if (!opts) return -ENOMEM; *mnt_opts = opts; + is_alloc_opts = true; } - if (!s) - return -ENOMEM; + switch (token) { case Opt_context: if (opts->context || opts->defcontext) @@ -1019,6 +1023,8 @@ static int selinux_add_opt(int token, const char *s, void **mnt_opts) } return 0; Einval: + if (is_alloc_opts) + kfree(opts); pr_warn(SEL_MOUNT_FAIL_MSG); return -EINVAL; }
This patch try to fix potential memleak in error branch. Signed-off-by: Bernard Zhao <bernard@vivo.com> --- security/selinux/hooks.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)