Limit maximum multipart/form-data pairs and files

A malicious user could inject an infinite number of empty files or
key/value pairs into a request in order to exhaust the device's
resources.

doc/man7/libweb_handler.7

@@ -76,6 +76,7 @@ struct handler_cfg
     int (*\fIlength\fP)(unsigned long long len, const struct http_cookie *c, struct http_response *r, void *user);
     void *\fIuser\fP;
     size_t \fImax_headers\fP;
+    struct http_cfg_post \fIpost\fP;
 };
 .EE
 .in
@@ -83,9 +84,10 @@ struct handler_cfg
 
 .IR tmpdir ,
 .IR length ,
-.I user
-and
+.IR user ,
 .I max_headers
+and
+.I post
 are passed directly to the
 .I struct http_cfg
 object used to initialize a

doc/man7/libweb_http.7

@@ -94,6 +94,11 @@ struct http_cfg
     const char *\fItmpdir\fP;
     void *\fIuser\fP;
     size_t \fImax_headers\fP;
+
+    struct http_cfg_post
+    {
+        size_t \fImax_pairs\fP, \fImax_files\fP;
+    } \fIpost\fP;
 };
 .EE
 .in
@@ -221,6 +226,31 @@ Any extra headers sent by the client outside this maximum value shall be
 silently ignored by
 .IR libweb .
 
+.I post
+contains configuration parameters specific to
+.B POST
+requests:
+
+.I max_pairs
+refers to the maximum number of key/value pairs that shall be accepted by
+.I libweb
+on
+.B POST
+.IR multipart/form-data -encoded
+requests. If the maximum number of pairs is exceeded by the request,
+.I libweb
+shall terminate the connection.
+
+.I max_files
+refers to the maximum number of files that shall be accepted by
+.I libweb
+on
+.B POST
+.IR multipart/form-data -encoded
+requests. If the maximum number of files is exceeded by the request,
+.I libweb
+shall terminate the connection.
+
 .SS HTTP payload
 
 When a client submits a request to the server,

handler.c

@@ -110,7 +110,8 @@ static struct client *find_or_alloc_client(struct handler *const h,
         .length = on_length,
         .user = ret,
         .tmpdir = h->cfg.tmpdir,
-        .max_headers = h->cfg.max_headers
+        .max_headers = h->cfg.max_headers,
+        .post = h->cfg.post
     };
 
     *ret = (const struct client)

http.c

@@ -1728,7 +1728,16 @@ static int apply_from_file(struct http_ctx *const h, struct form *const f)
 
     m->f = NULL;
 
+    const struct http_cfg_post *const cfg = &h->cfg.post;
     const size_t n = m->nfiles + 1;
+
+    if (n > cfg->max_files)
+    {
+        fprintf(stderr, "%s: exceeded maximum number of files (%zu)\n",
+            __func__, cfg->max_files);
+        return 1;
+    }
+
     struct http_post_file *const files = realloc(m->files,
         n * sizeof *m->files);
 
@@ -1777,10 +1786,17 @@ static int apply_from_mem(struct http_ctx *const h, struct form *const f)
     if (name_exists(m, f))
         return 1;
 
+    const struct http_cfg_post *const cfg = &h->cfg.post;
     struct http_post_pair *pairs, *p;
     const size_t n = m->npairs + 1;
 
-    if (!(f->value = strndup(h->line, m->written)))
+    if (n > cfg->max_pairs)
+    {
+        fprintf(stderr, "%s: exceeded maximum number of pairs (%zu)\n",
+            __func__, cfg->max_pairs);
+        return 1;
+    }
+    else if (!(f->value = strndup(h->line, m->written)))
     {
         fprintf(stderr, "%s: strndup(3): %s\n", __func__, strerror(errno));
         return -1;

include/libweb/handler.h

@@ -14,6 +14,7 @@ struct handler_cfg
         struct http_response *r, void *user);
     void *user;
     size_t max_headers;
+    struct http_cfg_post post;
 };
 
 struct handler *handler_alloc(const struct handler_cfg *cfg);

include/libweb/http.h

@@ -106,6 +106,11 @@ struct http_cfg
     const char *tmpdir;
     void *user;
     size_t max_headers;
+
+    struct http_cfg_post
+    {
+        size_t max_pairs, max_files;
+    } post;
 };
 
 struct http_ctx *http_alloc(const struct http_cfg *cfg);