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util-src/ringbuffer.c @ 11665:148075532021
net.server_epoll: Prevent stack overflow of opportunistic writes
net.http.files serving a big enough file on a fast enough connection
with opportunistic_writes enabled could trigger a stack overflow through
repeatedly serving more data that immediately gets sent, draining the
buffer and triggering more data to be sent. This also blocked the server
on a single task until completion or an error.
This change prevents nested opportunistic writes, which should prevent
the stack overflow, at the cost of reduced download speed, but this is
unlikely to be noticeable outside of Gbit networks. Speed at the cost of
blocking other processing is not worth it, especially with the risk of
stack overflow.
author | Kim Alvefur <zash@zash.se> |
---|---|
date | Sun, 11 Jul 2021 09:39:21 +0200 |
parent | 10953:c3b3ac63f4c3 |
child | 12575:1f6f05a98fcd |
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#include <stdlib.h> #include <unistd.h> #include <string.h> #include <lua.h> #include <lauxlib.h> #if (LUA_VERSION_NUM < 504) #define luaL_pushfail lua_pushnil #endif typedef struct { size_t rpos; /* read position */ size_t wpos; /* write position */ size_t alen; /* allocated size */ size_t blen; /* current content size */ char buffer[]; } ringbuffer; /* Translate absolute idx to a wrapped index within the buffer, based on current read position */ static int wrap_pos(const ringbuffer *b, const long idx, long *pos) { if(idx > (long)b->blen) { return 0; } if(idx + (long)b->rpos > (long)b->alen) { *pos = idx - (b->alen - b->rpos); } else { *pos = b->rpos + idx; } return 1; } static int calc_splice_positions(const ringbuffer *b, long start, long end, long *out_start, long *out_end) { if(start < 0) { start = 1 + start + b->blen; } if(start <= 0) { start = 1; } if(end < 0) { end = 1 + end + b->blen; } if(end > (long)b->blen) { end = b->blen; } if(start < 1) { start = 1; } if(start > end) { return 0; } start = start - 1; if(!wrap_pos(b, start, out_start)) { return 0; } if(!wrap_pos(b, end, out_end)) { return 0; } return 1; } static void writechar(ringbuffer *b, char c) { b->blen++; b->buffer[(b->wpos++) % b->alen] = c; } /* make sure position counters stay within the allocation */ static void modpos(ringbuffer *b) { b->rpos = b->rpos % b->alen; b->wpos = b->wpos % b->alen; } static int find(ringbuffer *b, const char *s, size_t l) { size_t i, j; int m; if(b->rpos == b->wpos) { /* empty */ return 0; } /* look for a matching first byte */ for(i = 0; i <= b->blen - l; i++) { if(b->buffer[(b->rpos + i) % b->alen] == *s) { m = 1; /* check if the following byte also match */ for(j = 1; j < l; j++) if(b->buffer[(b->rpos + i + j) % b->alen] != s[j]) { m = 0; break; } if(m) { return i + l; } } } return 0; } /* * Find first position of a substring in buffer * (buffer, string) -> number */ static int rb_find(lua_State *L) { size_t l, m; ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); const char *s = luaL_checklstring(L, 2, &l); m = find(b, s, l); if(m > 0) { lua_pushinteger(L, m); return 1; } return 0; } /* * Move read position forward without returning the data * (buffer, number) -> boolean */ static int rb_discard(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); size_t r = luaL_checkinteger(L, 2); if(r > b->blen) { lua_pushboolean(L, 0); return 1; } b->blen -= r; b->rpos += r; modpos(b); lua_pushboolean(L, 1); return 1; } /* * Read bytes from buffer * (buffer, number, boolean?) -> string */ static int rb_read(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); size_t r = luaL_checkinteger(L, 2); int peek = lua_toboolean(L, 3); if(r > b->blen) { luaL_pushfail(L); return 1; } if((b->rpos + r) > b->alen) { /* Substring wraps around to the beginning of the buffer */ lua_pushlstring(L, &b->buffer[b->rpos], b->alen - b->rpos); lua_pushlstring(L, b->buffer, r - (b->alen - b->rpos)); lua_concat(L, 2); } else { lua_pushlstring(L, &b->buffer[b->rpos], r); } if(!peek) { b->blen -= r; b->rpos += r; modpos(b); } return 1; } /* * Read buffer until first occurrence of a substring * (buffer, string) -> string */ static int rb_readuntil(lua_State *L) { size_t l, m; ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); const char *s = luaL_checklstring(L, 2, &l); m = find(b, s, l); if(m > 0) { lua_settop(L, 1); lua_pushinteger(L, m); return rb_read(L); } return 0; } /* * Write bytes into the buffer * (buffer, string) -> integer */ static int rb_write(lua_State *L) { size_t l, w = 0; ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); const char *s = luaL_checklstring(L, 2, &l); /* Does `l` bytes fit? */ if((l + b->blen) > b->alen) { luaL_pushfail(L); return 1; } while(l-- > 0) { writechar(b, *s++); w++; } modpos(b); lua_pushinteger(L, w); return 1; } static int rb_tostring(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); lua_pushfstring(L, "ringbuffer: %p %d/%d", b, b->blen, b->alen); return 1; } static int rb_sub(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); long start = luaL_checkinteger(L, 2); long end = luaL_optinteger(L, 3, -1); long wrapped_start, wrapped_end; if(!calc_splice_positions(b, start, end, &wrapped_start, &wrapped_end)) { lua_pushstring(L, ""); } else if(wrapped_end <= wrapped_start) { lua_pushlstring(L, &b->buffer[wrapped_start], b->alen - wrapped_start); lua_pushlstring(L, b->buffer, wrapped_end); lua_concat(L, 2); } else { lua_pushlstring(L, &b->buffer[wrapped_start], (wrapped_end - wrapped_start)); } return 1; } static int rb_byte(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); long start = luaL_optinteger(L, 2, 1); long end = luaL_optinteger(L, 3, start); long i; long wrapped_start, wrapped_end; if(calc_splice_positions(b, start, end, &wrapped_start, &wrapped_end)) { if(wrapped_end <= wrapped_start) { for(i = wrapped_start; i < (long)b->alen; i++) { lua_pushinteger(L, (unsigned char)b->buffer[i]); } for(i = 0; i < wrapped_end; i++) { lua_pushinteger(L, (unsigned char)b->buffer[i]); } return wrapped_end + (b->alen - wrapped_start); } else { for(i = wrapped_start; i < wrapped_end; i++) { lua_pushinteger(L, (unsigned char)b->buffer[i]); } return wrapped_end - wrapped_start; } } return 0; } static int rb_length(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); lua_pushinteger(L, b->blen); return 1; } static int rb_size(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); lua_pushinteger(L, b->alen); return 1; } static int rb_free(lua_State *L) { ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt"); lua_pushinteger(L, b->alen - b->blen); return 1; } static int rb_new(lua_State *L) { lua_Integer size = luaL_optinteger(L, 1, sysconf(_SC_PAGESIZE)); luaL_argcheck(L, size > 0, 1, "positive integer expected"); ringbuffer *b = lua_newuserdata(L, sizeof(ringbuffer) + size); b->rpos = 0; b->wpos = 0; b->alen = size; b->blen = 0; luaL_getmetatable(L, "ringbuffer_mt"); lua_setmetatable(L, -2); return 1; } int luaopen_util_ringbuffer(lua_State *L) { #if (LUA_VERSION_NUM > 501) luaL_checkversion(L); #endif if(luaL_newmetatable(L, "ringbuffer_mt")) { lua_pushcfunction(L, rb_tostring); lua_setfield(L, -2, "__tostring"); lua_pushcfunction(L, rb_length); lua_setfield(L, -2, "__len"); lua_createtable(L, 0, 7); /* __index */ { lua_pushcfunction(L, rb_find); lua_setfield(L, -2, "find"); lua_pushcfunction(L, rb_discard); lua_setfield(L, -2, "discard"); lua_pushcfunction(L, rb_read); lua_setfield(L, -2, "read"); lua_pushcfunction(L, rb_readuntil); lua_setfield(L, -2, "readuntil"); lua_pushcfunction(L, rb_write); lua_setfield(L, -2, "write"); lua_pushcfunction(L, rb_size); lua_setfield(L, -2, "size"); lua_pushcfunction(L, rb_length); lua_setfield(L, -2, "length"); lua_pushcfunction(L, rb_sub); lua_setfield(L, -2, "sub"); lua_pushcfunction(L, rb_byte); lua_setfield(L, -2, "byte"); lua_pushcfunction(L, rb_free); lua_setfield(L, -2, "free"); } lua_setfield(L, -2, "__index"); } lua_createtable(L, 0, 1); lua_pushcfunction(L, rb_new); lua_setfield(L, -2, "new"); return 1; }