Messages in this thread Patch in this message | | | From | 赵军奎 <> | Subject | 答复: [PATCH v2] security/selinux: fix pote ntial memleak in error branch | Date | Tue, 7 Dec 2021 12:05:49 +0000 |
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-----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.
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