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Subject[PATCH] ceph: fix allocation under spinlock in mount option parsing
Date
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@syzkaller.appspotmail.com
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
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
+ *
+ * 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 *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;
+}
+
/*
* 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);

/*
* 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 "/" */
char *fscache_uniq; /* default NULL */
};

--
2.24.1
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