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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id f8sm12699568pfq.178.2020.03.31.07.30.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 07:30:21 -0700 (PDT) Date: Mon, 30 Mar 2020 11:33:49 -0700 From: Kees Cook To: Alexey Gladkov Cc: LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexander Viro , Alexey Dobriyan , Alexey Gladkov , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , "Eric W . Biederman" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Linus Torvalds , Oleg Nesterov Subject: Re: [PATCH v11 8/9] proc: use human-readable values for hidehid Message-ID: <202003301132.EDD8329@keescook> References: <20200327172331.418878-9-gladkov.alexey@gmail.com> <20200330111235.154182-1-gladkov.alexey@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200330111235.154182-1-gladkov.alexey@gmail.com> Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Mon, Mar 30, 2020 at 01:12:35PM +0200, Alexey Gladkov wrote: > The hidepid parameter values are becoming more and more and it becomes > difficult to remember what each new magic number means. > > Suggested-by: Andy Lutomirski > Signed-off-by: Alexey Gladkov > --- > Documentation/filesystems/proc.txt | 52 +++++++++++++++--------------- > fs/proc/inode.c | 15 ++++++++- > fs/proc/root.c | 36 +++++++++++++++++++-- > 3 files changed, 73 insertions(+), 30 deletions(-) > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > index bd0e0ab85048..af47672cb2cb 100644 > --- a/Documentation/filesystems/proc.txt > +++ b/Documentation/filesystems/proc.txt > @@ -2025,28 +2025,28 @@ The following mount options are supported: > gid= Set the group authorized to learn processes information. > subset= Show only the specified subset of procfs. > > -hidepid=0 means classic mode - everybody may access all /proc// directories > -(default). > - > -hidepid=1 means users may not access any /proc// directories but their > -own. Sensitive files like cmdline, sched*, status are now protected against > -other users. This makes it impossible to learn whether any user runs > -specific program (given the program doesn't reveal itself by its behaviour). > -As an additional bonus, as /proc//cmdline is unaccessible for other users, > -poorly written programs passing sensitive information via program arguments are > -now protected against local eavesdroppers. > - > -hidepid=2 means hidepid=1 plus all /proc// will be fully invisible to other > -users. It doesn't mean that it hides a fact whether a process with a specific > -pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), > -but it hides process' uid and gid, which may be learned by stat()'ing > -/proc// otherwise. It greatly complicates an intruder's task of gathering > -information about running processes, whether some daemon runs with elevated > -privileges, whether other user runs some sensitive program, whether other users > -run any program at all, etc. > - > -hidepid=4 means that procfs should only contain /proc// directories > -that the caller can ptrace. > +hidepid=off or hidepid=0 means classic mode - everybody may access all > +/proc// directories (default). > + > +hidepid=noaccess or hidepid=1 means users may not access any /proc// > +directories but their own. Sensitive files like cmdline, sched*, status are now > +protected against other users. This makes it impossible to learn whether any > +user runs specific program (given the program doesn't reveal itself by its > +behaviour). As an additional bonus, as /proc//cmdline is unaccessible for > +other users, poorly written programs passing sensitive information via program > +arguments are now protected against local eavesdroppers. > + > +hidepid=invisible or hidepid=2 means hidepid=noaccess plus all /proc// will > +be fully invisible to other users. It doesn't mean that it hides a fact whether > +a process with a specific pid value exists (it can be learned by other means, > +e.g. by "kill -0 $PID"), but it hides process' uid and gid, which may be learned > +by stat()'ing /proc// otherwise. It greatly complicates an intruder's task > +of gathering information about running processes, whether some daemon runs with > +elevated privileges, whether other user runs some sensitive program, whether > +other users run any program at all, etc. > + > +hidepid=ptraceable or hidepid=4 means that procfs should only contain > +/proc// directories that the caller can ptrace. > > gid= defines a group authorized to learn processes information otherwise > prohibited by hidepid=. If you use some daemon like identd which needs to learn > @@ -2093,8 +2093,8 @@ creates a new procfs instance. Mount options affect own procfs instance. > It means that it became possible to have several procfs instances > displaying tasks with different filtering options in one pid namespace. > > -# mount -o hidepid=2 -t proc proc /proc > -# mount -o hidepid=1 -t proc proc /tmp/proc > +# mount -o hidepid=invisible -t proc proc /proc > +# mount -o hidepid=noaccess -t proc proc /tmp/proc > # grep ^proc /proc/mounts > -proc /proc proc rw,relatime,hidepid=2 0 0 > -proc /tmp/proc proc rw,relatime,hidepid=1 0 0 > +proc /proc proc rw,relatime,hidepid=invisible 0 0 > +proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0 > diff --git a/fs/proc/inode.c b/fs/proc/inode.c > index e6577ce6027b..d38a9e592352 100644 > --- a/fs/proc/inode.c > +++ b/fs/proc/inode.c > @@ -24,6 +24,7 @@ > #include > #include > #include > +#include > > #include > > @@ -165,6 +166,18 @@ void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock > deactivate_super(old_sb); > } > > +static inline const char *hidepid2str(int v) > +{ > + switch (v) { > + case HIDEPID_OFF: return "off"; > + case HIDEPID_NO_ACCESS: return "noaccess"; > + case HIDEPID_INVISIBLE: return "invisible"; > + case HIDEPID_NOT_PTRACEABLE: return "ptraceable"; > + } > + WARN_ONCE(1, "bad hide_pid value: %d\n", v); > + return "unknown"; > +} > + > static int proc_show_options(struct seq_file *seq, struct dentry *root) > { > struct proc_fs_info *fs_info = proc_sb_info(root->d_sb); > @@ -172,7 +185,7 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root) > if (!gid_eq(fs_info->pid_gid, GLOBAL_ROOT_GID)) > seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fs_info->pid_gid)); > if (fs_info->hide_pid != HIDEPID_OFF) > - seq_printf(seq, ",hidepid=%u", fs_info->hide_pid); > + seq_printf(seq, ",hidepid=%s", hidepid2str(fs_info->hide_pid)); > if (fs_info->pidonly != PROC_PIDONLY_OFF) > seq_printf(seq, ",subset=pid"); > > diff --git a/fs/proc/root.c b/fs/proc/root.c > index dbcd96f07c7a..ba782d6e6197 100644 > --- a/fs/proc/root.c > +++ b/fs/proc/root.c > @@ -45,7 +45,7 @@ enum proc_param { > > static const struct fs_parameter_spec proc_fs_parameters[] = { > fsparam_u32("gid", Opt_gid), > - fsparam_u32("hidepid", Opt_hidepid), > + fsparam_string("hidepid", Opt_hidepid), > fsparam_string("subset", Opt_subset), > {} > }; > @@ -58,6 +58,35 @@ static inline int valid_hidepid(unsigned int value) > value == HIDEPID_NOT_PTRACEABLE); > } > > +static int proc_parse_hidepid_param(struct fs_context *fc, struct fs_parameter *param) > +{ > + struct proc_fs_context *ctx = fc->fs_private; > + struct fs_parameter_spec hidepid_u32_spec = fsparam_u32("hidepid", Opt_hidepid); > + struct fs_parse_result result; > + int base = (unsigned long)hidepid_u32_spec.data; > + > + if (param->type != fs_value_is_string) > + return invalf(fc, "proc: unexpected type of hidepid value\n"); > + > + if (!kstrtouint(param->string, base, &result.uint_32)) { > + ctx->hidepid = result.uint_32; If it were me, I'd put this valid_hidepid() test inside here, then the parsing really is entirely done by this function. Otherwise, the validation is spread into proc_parse_param() which seems weird. But either way: Reviewed-by: Kees Cook -Kees > + return 0; > + } > + > + if (!strcmp(param->string, "off")) > + ctx->hidepid = HIDEPID_OFF; > + else if (!strcmp(param->string, "noaccess")) > + ctx->hidepid = HIDEPID_NO_ACCESS; > + else if (!strcmp(param->string, "invisible")) > + ctx->hidepid = HIDEPID_INVISIBLE; > + else if (!strcmp(param->string, "ptraceable")) > + ctx->hidepid = HIDEPID_NOT_PTRACEABLE; > + else > + return invalf(fc, "proc: unknown value of hidepid - %s\n", param->string); > + > + return 0; > +} > + > static int proc_parse_subset_param(struct fs_context *fc, char *value) > { > struct proc_fs_context *ctx = fc->fs_private; > @@ -97,9 +126,10 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) > break; > > case Opt_hidepid: > - if (!valid_hidepid(result.uint_32)) > + if (proc_parse_hidepid_param(fc, param)) > + return -EINVAL; > + if (!valid_hidepid(ctx->hidepid)) > return invalf(fc, "proc: unknown value of hidepid.\n"); > - ctx->hidepid = result.uint_32; > break; > > case Opt_subset: > -- > 2.25.2 > -- Kees Cook