Re: [PATCH] ceph: fix allocation under spinlock in mount option parsing

From: Ilya Dryomov
Date: Tue Feb 11 2020 - 04:15:25 EST

Next message: Bartosz Golaszewski: "[RESEND PATCH v6 5/7] gpiolib: provide a dedicated function for setting lineinfo"
Previous message: Marc Zyngier: "Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code"
In reply to: Xiubo Li: "Re: [PATCH] ceph: fix allocation under spinlock in mount option parsing"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On Fri, Feb 7, 2020 at 10:49 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> Al and syzbot reported that 4fbc0c711b24 (ceph: remove the extra slashes
> in the server path) had caused a regression where an allocation could be
> done under spinlock.
>
> Fix this by keeping a canonicalized version of the path in the mount
> options. Then we can simply compare those without making copies at all
> during the comparison.
>
> Fixes: 4fbc0c711b24 ("ceph: remove the extra slashes in the server path")
> Reported-by: syzbot+98704a51af8e3d9425a9@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/ceph/super.c | 170 ++++++++++++++++++++++--------------------------
> fs/ceph/super.h | 1 +
> 2 files changed, 79 insertions(+), 92 deletions(-)
>
> diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> index 5fa28e98d2b8..196d547c7054 100644
> --- a/fs/ceph/super.c
> +++ b/fs/ceph/super.c
> @@ -208,6 +208,69 @@ struct ceph_parse_opts_ctx {
> struct ceph_mount_options *opts;
> };
>
> +/**
> + * canonicalize_path - Remove the extra slashes in the server path
> + * @server_path: the server path and could be NULL

Hi Jeff,

It doesn't look like server_path can be NULL, and the code doesn't
handle that either.

> + *
> + * Return NULL if the path is NULL or only consists of "/", or a string
> + * without any extra slashes including the leading slash(es) and the

It can return an error, so this should say "string, NULL or error", but
see below.

> + * slash(es) at the end of the server path, such as:
> + * "//dir1////dir2///" --> "dir1/dir2"
> + */
> +static char *canonicalize_path(const char *server_path)
> +{
> + const char *path = server_path;
> + const char *cur, *end;
> + char *buf, *p;
> + int len;
> +
> + /* remove all the leading slashes */
> + while (*path == '/')
> + path++;
> +
> + /* if the server path only consists of slashes */
> + if (*path == '\0')
> + return NULL;
> +
> + len = strlen(path);
> +
> + buf = kmalloc(len + 1, GFP_KERNEL);
> + if (!buf)
> + return ERR_PTR(-ENOMEM);
> +
> + end = path + len;
> + p = buf;
> + do {
> + cur = strchr(path, '/');
> + if (!cur)
> + cur = end;
> +
> + len = cur - path;
> +
> + /* including one '/' */
> + if (cur != end)
> + len += 1;
> +
> + memcpy(p, path, len);
> + p += len;
> +
> + while (cur <= end && *cur == '/')
> + cur++;
> + path = cur;
> + } while (path < end);
> +
> + *p = '\0';
> +
> + /*
> + * remove the last slash if there has and just to make sure that
> + * we will get something like "dir1/dir2"
> + */
> + if (*(--p) == '/')
> + *p = '\0';
> +
> + return buf;
> +}

I realize that you just adapted the existing function, but it really
looks like a mouthful -- both the signature (string, NULL or error)
and the code. It could be a lot more concise...

> +
> /*
> * Parse the source parameter. Distinguish the server list from the path.
> *
> @@ -230,15 +293,23 @@ static int ceph_parse_source(struct fs_parameter *param, struct fs_context *fc)
>
> dev_name_end = strchr(dev_name, '/');
> if (dev_name_end) {
> - kfree(fsopt->server_path);
>

Blank line.

> /*
> * The server_path will include the whole chars from userland
> * including the leading '/'.
> */
> + kfree(fsopt->server_path);
> fsopt->server_path = kstrdup(dev_name_end, GFP_KERNEL);
> if (!fsopt->server_path)
> return -ENOMEM;
> +
> + kfree(fsopt->canon_path);
> + fsopt->canon_path = canonicalize_path(fsopt->server_path);
> + if (fsopt->canon_path && IS_ERR(fsopt->canon_path)) {
> + ret = PTR_ERR(fsopt->canon_path);
> + fsopt->canon_path = NULL;
> + return ret;
> + }
> } else {
> dev_name_end = dev_name + strlen(dev_name);
> }
> @@ -447,6 +518,7 @@ static void destroy_mount_options(struct ceph_mount_options *args)
> kfree(args->snapdir_name);
> kfree(args->mds_namespace);
> kfree(args->server_path);
> + kfree(args->canon_path);
> kfree(args->fscache_uniq);
> kfree(args);
> }
> @@ -462,73 +534,6 @@ static int strcmp_null(const char *s1, const char *s2)
> return strcmp(s1, s2);
> }
>
> -/**
> - * path_remove_extra_slash - Remove the extra slashes in the server path
> - * @server_path: the server path and could be NULL
> - *
> - * Return NULL if the path is NULL or only consists of "/", or a string
> - * without any extra slashes including the leading slash(es) and the
> - * slash(es) at the end of the server path, such as:
> - * "//dir1////dir2///" --> "dir1/dir2"
> - */
> -static char *path_remove_extra_slash(const char *server_path)
> -{
> - const char *path = server_path;
> - const char *cur, *end;
> - char *buf, *p;
> - int len;
> -
> - /* if the server path is omitted */
> - if (!path)
> - return NULL;
> -
> - /* remove all the leading slashes */
> - while (*path == '/')
> - path++;
> -
> - /* if the server path only consists of slashes */
> - if (*path == '\0')
> - return NULL;
> -
> - len = strlen(path);
> -
> - buf = kmalloc(len + 1, GFP_KERNEL);
> - if (!buf)
> - return ERR_PTR(-ENOMEM);
> -
> - end = path + len;
> - p = buf;
> - do {
> - cur = strchr(path, '/');
> - if (!cur)
> - cur = end;
> -
> - len = cur - path;
> -
> - /* including one '/' */
> - if (cur != end)
> - len += 1;
> -
> - memcpy(p, path, len);
> - p += len;
> -
> - while (cur <= end && *cur == '/')
> - cur++;
> - path = cur;
> - } while (path < end);
> -
> - *p = '\0';
> -
> - /*
> - * remove the last slash if there has and just to make sure that
> - * we will get something like "dir1/dir2"
> - */
> - if (*(--p) == '/')
> - *p = '\0';
> -
> - return buf;
> -}
> -
> static int compare_mount_options(struct ceph_mount_options *new_fsopt,
> struct ceph_options *new_opt,
> struct ceph_fs_client *fsc)
> @@ -536,7 +541,6 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
> struct ceph_mount_options *fsopt1 = new_fsopt;
> struct ceph_mount_options *fsopt2 = fsc->mount_options;
> int ofs = offsetof(struct ceph_mount_options, snapdir_name);
> - char *p1, *p2;
> int ret;
>
> ret = memcmp(fsopt1, fsopt2, ofs);
> @@ -546,21 +550,12 @@ static int compare_mount_options(struct ceph_mount_options *new_fsopt,
> ret = strcmp_null(fsopt1->snapdir_name, fsopt2->snapdir_name);
> if (ret)
> return ret;
> +
> ret = strcmp_null(fsopt1->mds_namespace, fsopt2->mds_namespace);
> if (ret)
> return ret;
>
> - p1 = path_remove_extra_slash(fsopt1->server_path);
> - if (IS_ERR(p1))
> - return PTR_ERR(p1);
> - p2 = path_remove_extra_slash(fsopt2->server_path);
> - if (IS_ERR(p2)) {
> - kfree(p1);
> - return PTR_ERR(p2);
> - }
> - ret = strcmp_null(p1, p2);
> - kfree(p1);
> - kfree(p2);
> + ret = strcmp_null(fsopt1->canon_path, fsopt2->canon_path);
> if (ret)
> return ret;
>
> @@ -963,7 +958,9 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
> mutex_lock(&fsc->client->mount_mutex);
>
> if (!fsc->sb->s_root) {
> - const char *path, *p;
> + const char *path = fsc->mount_options->canon_path ?
> + fsc->mount_options->canon_path : "";
> +
> err = __ceph_open_session(fsc->client, started);
> if (err < 0)
> goto out;
> @@ -975,22 +972,11 @@ static struct dentry *ceph_real_mount(struct ceph_fs_client *fsc,
> goto out;
> }
>
> - p = path_remove_extra_slash(fsc->mount_options->server_path);
> - if (IS_ERR(p)) {
> - err = PTR_ERR(p);
> - goto out;
> - }
> - /* if the server path is omitted or just consists of '/' */
> - if (!p)
> - path = "";
> - else
> - path = p;
> dout("mount opening path '%s'\n", path);
>
> ceph_fs_debugfs_init(fsc);
>
> root = open_root_dentry(fsc, path, started);
> - kfree(p);
> if (IS_ERR(root)) {
> err = PTR_ERR(root);
> goto out;
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index e8f891770f9d..70aa32cfb64d 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -94,6 +94,7 @@ struct ceph_mount_options {
> char *snapdir_name; /* default ".snap" */
> char *mds_namespace; /* default NULL */
> char *server_path; /* default "/" */
> + char *canon_path; /* default "/" */

Why keep both the original and canon_path around? It looks like
the only remaining use of server_path is in create_session_open_msg().
Since that's just metadata, I think we can safely switch it over.

Also, the comment is misleading. The default is NULL (which _means_
"/" for metadata purposes but "/" is never stored here).

I'll post what I have in mind as a patch shortly.

Thanks,

Ilya

Next message: Bartosz Golaszewski: "[RESEND PATCH v6 5/7] gpiolib: provide a dedicated function for setting lineinfo"
Previous message: Marc Zyngier: "Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code"
In reply to: Xiubo Li: "Re: [PATCH] ceph: fix allocation under spinlock in mount option parsing"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]