4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <f...@strlen.de>

commit b1d0a5d0cba4597c0394997b2d5fced3e3841b4e upstream.

recent and hashlimit both create /proc files, but only check that
name is 0 terminated.

This can trigger WARN() from procfs when name is "" or "/".
Add helper for this and then use it for both.

Cc: Eric Dumazet <eric.duma...@gmail.com>
Reported-by: Eric Dumazet <eric.duma...@gmail.com>
Reported-by: <syzbot+0502b00edac2a0680...@syzkaller.appspotmail.com>
Signed-off-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 include/linux/netfilter/x_tables.h |    2 ++
 net/netfilter/x_tables.c           |   30 ++++++++++++++++++++++++++++++
 net/netfilter/xt_hashlimit.c       |    5 +++--
 net/netfilter/xt_recent.c          |    6 +++---
 4 files changed, 38 insertions(+), 5 deletions(-)

--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -247,6 +247,8 @@ unsigned int *xt_alloc_entry_offsets(uns
 bool xt_find_jump_offset(const unsigned int *offsets,
                         unsigned int target, unsigned int size);
 
+int xt_check_proc_name(const char *name, unsigned int size);
+
 int xt_check_match(struct xt_mtchk_param *, unsigned int size, u_int8_t proto,
                   bool inv_proto);
 int xt_check_target(struct xt_tgchk_param *, unsigned int size, u_int8_t proto,
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -366,6 +366,36 @@ textify_hooks(char *buf, size_t size, un
        return buf;
 }
 
+/**
+ * xt_check_proc_name - check that name is suitable for /proc file creation
+ *
+ * @name: file name candidate
+ * @size: length of buffer
+ *
+ * some x_tables modules wish to create a file in /proc.
+ * This function makes sure that the name is suitable for this
+ * purpose, it checks that name is NUL terminated and isn't a 'special'
+ * name, like "..".
+ *
+ * returns negative number on error or 0 if name is useable.
+ */
+int xt_check_proc_name(const char *name, unsigned int size)
+{
+       if (name[0] == '\0')
+               return -EINVAL;
+
+       if (strnlen(name, size) == size)
+               return -ENAMETOOLONG;
+
+       if (strcmp(name, ".") == 0 ||
+           strcmp(name, "..") == 0 ||
+           strchr(name, '/'))
+               return -EINVAL;
+
+       return 0;
+}
+EXPORT_SYMBOL(xt_check_proc_name);
+
 int xt_check_match(struct xt_mtchk_param *par,
                   unsigned int size, u_int8_t proto, bool inv_proto)
 {
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -668,8 +668,9 @@ static int hashlimit_mt_check(const stru
 
        if (info->cfg.gc_interval == 0 || info->cfg.expire == 0)
                return -EINVAL;
-       if (info->name[sizeof(info->name)-1] != '\0')
-               return -EINVAL;
+       ret = xt_check_proc_name(info->name, sizeof(info->name));
+       if (ret)
+               return ret;
        if (par->family == NFPROTO_IPV4) {
                if (info->cfg.srcmask > 32 || info->cfg.dstmask > 32)
                        return -EINVAL;
--- a/net/netfilter/xt_recent.c
+++ b/net/netfilter/xt_recent.c
@@ -364,9 +364,9 @@ static int recent_mt_check(const struct
                        info->hit_count, XT_RECENT_MAX_NSTAMPS - 1);
                return -EINVAL;
        }
-       if (info->name[0] == '\0' ||
-           strnlen(info->name, XT_RECENT_NAME_LEN) == XT_RECENT_NAME_LEN)
-               return -EINVAL;
+       ret = xt_check_proc_name(info->name, sizeof(info->name));
+       if (ret)
+               return ret;
 
        if (ip_pkt_list_tot && info->hit_count < ip_pkt_list_tot)
                nstamp_mask = roundup_pow_of_two(ip_pkt_list_tot) - 1;


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