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Message-ID: <d93d2eb8-7d71-43f9-1424-932edaf218e1@oracle.com>
Date: Mon, 22 Nov 2021 16:07:59 -0800
From: Stephen Brennan <stephen.s.brennan@...cle.com>
To: Alexey Dobriyan <adobriyan@...il.com>, viro@...iv.linux.org.uk,
ebiederm@...ssion.com
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] proc: "mount -o lookup=..." support
Hi Alexey,
On 11/22/21 11:23, Alexey Dobriyan wrote:
> Docker implements MaskedPaths configuration option
>
> https://github.com/estesp/docker/blob/9c15e82f19b0ad3c5fe8617a8ec2dddc6639f40a/oci/defaults.go#L97
>
> to disable certain /proc files. It does overmount with /dev/null per
> masked file.
>
> Give them proper mount option which selectively disables lookup/readdir
> so that MaskedPaths doesn't need to be updated as time goes on.
>
> Syntax is
>
> mount -t proc proc -o lookup=cpuinfo/uptime /proc
>
> # ls /proc
> ...
> dr-xr-xr-x 8 root root 0 Nov 22 21:12 995
> -r--r--r-- 1 root root 0 Nov 22 21:12 cpuinfo
> lrwxrwxrwx 1 root root 0 Nov 22 21:12 self -> 1163
> lrwxrwxrwx 1 root root 0 Nov 22 21:12 thread-self -> 1163/task/1163
> -r--r--r-- 1 root root 0 Nov 22 21:12 uptime
>
> Works at top level only (1 lookup list per superblock)
> Trailing slash is optional but saves 1 allocation.
>
> TODO:
> think what to do with dcache entries across "mount -o remount,lookup=".
>
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
>
> fs/proc/generic.c | 19 +++++--
> fs/proc/internal.h | 23 +++++++++
> fs/proc/proc_net.c | 2
> fs/proc/root.c | 115 ++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/proc_fs.h | 2
> 5 files changed, 152 insertions(+), 9 deletions(-)
>
> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -282,7 +282,7 @@ struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
> * for success..
> */
> int proc_readdir_de(struct file *file, struct dir_context *ctx,
> - struct proc_dir_entry *de)
> + struct proc_dir_entry *de, const struct proc_lookup_list *ll)
> {
> int i;
>
> @@ -305,14 +305,18 @@ int proc_readdir_de(struct file *file, struct dir_context *ctx,
>
> do {
> struct proc_dir_entry *next;
> +
> pde_get(de);
> read_unlock(&proc_subdir_lock);
> - if (!dir_emit(ctx, de->name, de->namelen,
> - de->low_ino, de->mode >> 12)) {
> - pde_put(de);
> - return 0;
> +
> + if (ll ? in_lookup_list(ll, de->name, de->namelen) : true) {
This looks a bit odd, what about the following?
if (!ll || in_lookup_list(ll, de->name, de->namelen))
But this is maybe just a personal preference.
> + if (!dir_emit(ctx, de->name, de->namelen, de->low_ino, de->mode >> 12)) {
> + pde_put(de);
> + return 0;
> + }
> + ctx->pos++;
> }
> - ctx->pos++;
> +
> read_lock(&proc_subdir_lock);
> next = pde_subdir_next(de);
> pde_put(de);
> @@ -330,7 +334,8 @@ int proc_readdir(struct file *file, struct dir_context *ctx)
> if (fs_info->pidonly == PROC_PIDONLY_ON)
> return 1;
>
> - return proc_readdir_de(file, ctx, PDE(inode));
> + return proc_readdir_de(file, ctx, PDE(inode),
> + PDE(inode) == &proc_root ? fs_info->lookup_list : NULL);
> }
>
> /*
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -190,7 +190,7 @@ struct proc_dir_entry *proc_register(struct proc_dir_entry *dir,
> extern struct dentry *proc_lookup(struct inode *, struct dentry *, unsigned int);
> struct dentry *proc_lookup_de(struct inode *, struct dentry *, struct proc_dir_entry *);
> extern int proc_readdir(struct file *, struct dir_context *);
> -int proc_readdir_de(struct file *, struct dir_context *, struct proc_dir_entry *);
> +int proc_readdir_de(struct file *, struct dir_context *, struct proc_dir_entry *, const struct proc_lookup_list *);
>
> static inline void pde_get(struct proc_dir_entry *pde)
> {
> @@ -318,3 +318,24 @@ static inline void pde_force_lookup(struct proc_dir_entry *pde)
> /* /proc/net/ entries can be changed under us by setns(CLONE_NEWNET) */
> pde->proc_dops = &proc_net_dentry_ops;
> }
> +
> +/*
> + * "cpuinfo", "uptime" is represented as
> + *
> + * (u8[]){
> + * 7, 'c', 'p', 'u', 'i', 'n', 'f', 'o',
> + * 6, 'u', 'p', 't', 'i', 'm', 'e',
> + * 0
> + * }
> + */
> +struct proc_lookup_list {
> + u8 len;
> + char str[];
> +};
> +
> +static inline struct proc_lookup_list *lookup_list_next(const struct proc_lookup_list *ll)
> +{
> + return (struct proc_lookup_list *)((void *)ll + 1 + ll->len);
> +}
> +
> +bool in_lookup_list(const struct proc_lookup_list *ll, const char *str, unsigned int len);
> --- a/fs/proc/proc_net.c
> +++ b/fs/proc/proc_net.c
> @@ -321,7 +321,7 @@ static int proc_tgid_net_readdir(struct file *file, struct dir_context *ctx)
> ret = -EINVAL;
> net = get_proc_task_net(file_inode(file));
> if (net != NULL) {
> - ret = proc_readdir_de(file, ctx, net->proc_net);
> + ret = proc_readdir_de(file, ctx, net->proc_net, NULL);
> put_net(net);
> }
> return ret;
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -35,18 +35,22 @@ struct proc_fs_context {
> enum proc_hidepid hidepid;
> int gid;
> enum proc_pidonly pidonly;
> + struct proc_lookup_list *lookup_list;
> + unsigned int lookup_list_len;
> };
>
> enum proc_param {
> Opt_gid,
> Opt_hidepid,
> Opt_subset,
> + Opt_lookup,
> };
>
> static const struct fs_parameter_spec proc_fs_parameters[] = {
> fsparam_u32("gid", Opt_gid),
> fsparam_string("hidepid", Opt_hidepid),
> fsparam_string("subset", Opt_subset),
> + fsparam_string("lookup", Opt_lookup),
> {}
> };
>
> @@ -112,6 +116,65 @@ static int proc_parse_subset_param(struct fs_context *fc, char *value)
> return 0;
> }
>
> +static int proc_parse_lookup_param(struct fs_context *fc, char *str0)
> +{
> + struct proc_fs_context *ctx = fc->fs_private;
> + struct proc_lookup_list *ll;
> + char *str;
> + const char *slash;
> + const char *src;
> + unsigned int len;
> + int rv;
> +
> + /* Force trailing slash, simplify loops below. */
> + len = strlen(str0);
> + if (len > 0 && str0[len - 1] == '/') {
> + str = str0;
> + } else {
> + str = kmalloc(len + 2, GFP_KERNEL);
> + if (!str) {
> + rv = -ENOMEM;
> + goto out;
> + }
> + memcpy(str, str0, len);
> + str[len] = '/';
> + str[len + 1] = '\0';
> + }
> +
> + len = 0;
> + for (src = str; (slash = strchr(src, '/')); src = slash + 1) {
> + if (slash - src >= 256) {
> + rv = -EINVAL;
> + goto out_free_str;
> + }
> + len += 1 + (slash - src);
> + }
> + len += 1;
> +
> + ctx->lookup_list = ll = kmalloc(len, GFP_KERNEL);
> + ctx->lookup_list_len = len;
> + if (!ll) {
> + rv = -ENOMEM;
> + goto out_free_str;
> + }
> +
> + for (src = str; (slash = strchr(src, '/')); src = slash + 1) {
> + ll->len = slash - src;
> + memcpy(ll->str, src, ll->len);
> + ll = lookup_list_next(ll);
> + }
> + ll->len = 0;
> +
> + rv = 0;
> +
> +out_free_str:
> + if (str != str0) {
> + kfree(str);
> + }
> +out:
> + return rv;
> +}
> +
> static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
> {
> struct proc_fs_context *ctx = fc->fs_private;
> @@ -137,6 +200,11 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
> return -EINVAL;
> break;
>
> + case Opt_lookup:
> + if (proc_parse_lookup_param(fc, param->string) < 0)
> + return -EINVAL;
> + break;
> +
> default:
> return -EINVAL;
> }
> @@ -157,6 +225,10 @@ static void proc_apply_options(struct proc_fs_info *fs_info,
> fs_info->hide_pid = ctx->hidepid;
> if (ctx->mask & (1 << Opt_subset))
> fs_info->pidonly = ctx->pidonly;
> + if (ctx->mask & (1 << Opt_lookup)) {
> + fs_info->lookup_list = ctx->lookup_list;
> + ctx->lookup_list = NULL;
> + }
> }
>
> static int proc_fill_super(struct super_block *s, struct fs_context *fc)
> @@ -234,11 +306,34 @@ static void proc_fs_context_free(struct fs_context *fc)
> struct proc_fs_context *ctx = fc->fs_private;
>
> put_pid_ns(ctx->pid_ns);
> + kfree(ctx->lookup_list);
> kfree(ctx);
> }
>
> +static int proc_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc)
> +{
> + struct proc_fs_context *src = fc->fs_private;
> + struct proc_fs_context *dst;
> +
> + dst = kmemdup(src, sizeof(struct proc_fs_context), GFP_KERNEL);
> + if (!dst) {
> + return -ENOMEM;
> + }
> +
> + get_pid_ns(dst->pid_ns);
> + dst->lookup_list = kmemdup(dst->lookup_list, dst->lookup_list_len, GFP_KERNEL);
If dst->lookup_list is NULL and dst->lookup_list_len is 0 (which seems
to be the default state if lookup= is not passed), then kmemdup will end
up calling __kmalloc_track_caller() with size 0. Each of the sl[auo]b
implementations returns ZERO_SIZE_POINTER in this case, which is just
((void *)16).
This is safe to pass to kfree et al. I was worried that if
ZERO_SIZE_POINTER gets copied into the proc_fs_info, then it could get
dereferenced and cause a nasty crash. But that can only happen if
Opt_lookup is in ctx->mask, at which point we're guaranteed that
lookup_list is not ZERO_SIZE_POINTER.
Just wanted to document why this is safe, as it caught my eye at first.
> + if (!dst->lookup_list) {
> + kfree(dst);
> + return -ENOMEM;
> + }
> +
> + fc->fs_private = dst;
> + return 0;
> +}
> +
> static const struct fs_context_operations proc_fs_context_ops = {
> .free = proc_fs_context_free,
> + .dup = proc_fs_context_dup,
From my reading of vfs_dup_fs_context, it seems like if the dup()
operation doesn't exist, the operation is simply bailed out and not
supported.
339 struct fs_context *vfs_dup_fs_context(struct fs_context *src_fc)
340 {
341 struct fs_context *fc;
342 int ret;
343
344 if (!src_fc->ops->dup)
345 return ERR_PTR(-EOPNOTSUPP);
So this patch is also adding support for the dup() operation where there
wasn't before. Is that significant to call out in the changelog or split
out as a separate patch?
Thanks,
Stephen
> .parse_param = proc_parse_param,
> .get_tree = proc_get_tree,
> .reconfigure = proc_reconfigure,
> @@ -274,6 +369,7 @@ static void proc_kill_sb(struct super_block *sb)
>
> kill_anon_super(sb);
> put_pid_ns(fs_info->pid_ns);
> + kfree(fs_info->lookup_list);
> kfree(fs_info);
> }
>
> @@ -317,11 +413,30 @@ static int proc_root_getattr(struct user_namespace *mnt_userns,
> return 0;
> }
>
> +bool in_lookup_list(const struct proc_lookup_list *ll, const char *str, unsigned int len)
> +{
> + while (ll->len > 0) {
> + if (ll->len == len && strncmp(ll->str, str, len) == 0) {
> + return true;
> + }
> + ll = lookup_list_next(ll);
> + }
> + return false;
> +}
> +
> static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentry, unsigned int flags)
> {
> + struct proc_fs_info *proc_sb = proc_sb_info(dir->i_sb);
> +
> if (!proc_pid_lookup(dentry, flags))
> return NULL;
>
> + /* Top level only for now */
> + if (proc_sb->lookup_list &&
> + !in_lookup_list(proc_sb->lookup_list, dentry->d_name.name, dentry->d_name.len)) {
> + return NULL;
> + }
> +
> return proc_lookup(dir, dentry, flags);
> }
>
> --- a/include/linux/proc_fs.h
> +++ b/include/linux/proc_fs.h
> @@ -10,6 +10,7 @@
> #include <linux/fs.h>
>
> struct proc_dir_entry;
> +struct proc_lookup_list;
> struct seq_file;
> struct seq_operations;
>
> @@ -65,6 +66,7 @@ struct proc_fs_info {
> kgid_t pid_gid;
> enum proc_hidepid hide_pid;
> enum proc_pidonly pidonly;
> + const struct proc_lookup_list *lookup_list;
> };
>
> static inline struct proc_fs_info *proc_sb_info(struct super_block *sb)
>
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