{"id":476585,"date":"2023-08-09T07:31:20","date_gmt":"2023-08-09T07:31:20","guid":{"rendered":""},"modified":"2023-09-05T11:13:02","modified_gmt":"2023-09-05T11:13:02","slug":"dangling-pointer","status":"publish","type":"wiki","link":"https:\/\/oneproxy.pro\/vn\/wiki\/dangling-pointer\/","title":{"rendered":"Con tr\u1ecf l\u01a1 l\u1eedng"},"content":{"rendered":"<p>Con tr\u1ecf l\u01a1 l\u1eedng l\u00e0 m\u1ed9t kh\u00e1i ni\u1ec7m quan tr\u1ecdng trong l\u1eadp tr\u00ecnh m\u00e1y t\u00ednh v\u00e0 \u0111\u1eb7c bi\u1ec7t ph\u00f9 h\u1ee3p v\u1edbi c\u00e1c ng\u00f4n ng\u1eef c\u1ea5p th\u1ea5p nh\u01b0 C v\u00e0 C++. N\u00f3 \u0111\u1ec1 c\u1eadp \u0111\u1ebfn m\u1ed9t con tr\u1ecf tr\u1ecf \u0111\u1ebfn m\u1ed9t v\u1ecb tr\u00ed b\u1ed9 nh\u1edb \u0111\u00e3 \u0111\u01b0\u1ee3c gi\u1ea3i ph\u00f3ng ho\u1eb7c gi\u1ea3i ph\u00f3ng, d\u1eabn \u0111\u1ebfn h\u00e0nh vi kh\u00f4ng mong mu\u1ed1n v\u00e0 ti\u1ec1m \u1ea9n nguy hi\u1ec3m khi ch\u01b0\u01a1ng tr\u00ecnh c\u1ed1 g\u1eafng truy c\u1eadp v\u00e0o b\u1ed9 nh\u1edb t\u1ea1i v\u1ecb tr\u00ed \u0111\u00f3. Hi\u1ec3u v\u00e0 qu\u1ea3n l\u00fd c\u00e1c con tr\u1ecf l\u01a1 l\u1eedng l\u00e0 \u0111i\u1ec1u c\u1ea7n thi\u1ebft \u0111\u1ec3 vi\u1ebft ph\u1ea7n m\u1ec1m an to\u00e0n v\u00e0 m\u1ea1nh m\u1ebd.<\/p>\n<h2>L\u1ecbch s\u1eed ngu\u1ed3n g\u1ed1c c\u1ee7a con tr\u1ecf l\u01a1 l\u1eedng v\u00e0 s\u1ef1 \u0111\u1ec1 c\u1eadp \u0111\u1ea7u ti\u00ean c\u1ee7a n\u00f3<\/h2>\n<p>Kh\u00e1i ni\u1ec7m con tr\u1ecf l\u01a1 l\u1eedng xu\u1ea5t hi\u1ec7n c\u00f9ng v\u1edbi s\u1ef1 ph\u00e1t tri\u1ec3n c\u1ee7a c\u00e1c ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh c\u1ea5p th\u1ea5p v\u00e0o nh\u1eefng n\u0103m 1970. C, m\u1ed9t ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng r\u1ed9ng r\u00e3i, cho ph\u00e9p thao t\u00e1c tr\u1ef1c ti\u1ebfp b\u1ed9 nh\u1edb th\u00f4ng qua c\u00e1c con tr\u1ecf, mang l\u1ea1i s\u1ef1 linh ho\u1ea1t nh\u01b0ng c\u0169ng mang \u0111\u1ebfn kh\u1ea3 n\u0103ng t\u1ea1o ra c\u00e1c con tr\u1ecf l\u01a1 l\u1eedng. Thu\u1eadt ng\u1eef \u201ccon tr\u1ecf l\u01a1 l\u1eedng\u201d c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c \u0111\u1eb7t ra trong nh\u1eefng ng\u00e0y \u0111\u1ea7u l\u1eadp tr\u00ecnh C khi c\u00e1c l\u1eadp tr\u00ecnh vi\u00ean g\u1eb7p kh\u00f3 kh\u0103n v\u1edbi vi\u1ec7c qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb theo c\u00e1ch th\u1ee7 c\u00f4ng.<\/p>\n<h2>Th\u00f4ng tin chi ti\u1ebft v\u1ec1 Con tr\u1ecf l\u01a1 l\u1eedng: M\u1edf r\u1ed9ng ch\u1ee7 \u0111\u1ec1<\/h2>\n<p>Con tr\u1ecf l\u01a1 l\u1eedng x\u1ea3y ra khi b\u1ed9 nh\u1edb \u0111\u01b0\u1ee3c gi\u1ea3i ph\u00f3ng ho\u1eb7c gi\u1ea3i ph\u00f3ng, nh\u01b0ng con tr\u1ecf v\u1eabn tham chi\u1ebfu \u0111\u1ebfn v\u1ecb tr\u00ed m\u00e0 b\u1ed9 nh\u1edb t\u1eebng \u1edf. \u0110i\u1ec1u n\u00e0y c\u00f3 th\u1ec3 x\u1ea3y ra khi:<\/p>\n<ol>\n<li>\n<p>B\u1ed9 nh\u1edb \u0111\u01b0\u1ee3c gi\u1ea3i ph\u00f3ng r\u00f5 r\u00e0ng b\u1eb1ng c\u00e1ch s\u1eed d\u1ee5ng c\u00e1c ch\u1ee9c n\u0103ng nh\u01b0 <code data-no-translation=\"\">free()<\/code> trong C ho\u1eb7c <code data-no-translation=\"\">delete<\/code> trong C++. Con tr\u1ecf tr\u1edf n\u00ean l\u01a1 l\u1eedng v\u00e0 m\u1ecdi n\u1ed7 l\u1ef1c ti\u1ebfp theo \u0111\u1ec3 truy c\u1eadp gi\u00e1 tr\u1ecb c\u1ee7a n\u00f3 \u0111\u1ec1u d\u1eabn \u0111\u1ebfn h\u00e0nh vi kh\u00f4ng x\u00e1c \u0111\u1ecbnh.<\/p>\n<\/li>\n<li>\n<p>Con tr\u1ecf kh\u00f4ng \u0111\u01b0\u1ee3c kh\u1edfi t\u1ea1o ho\u1eb7c \u0111\u1eb7t th\u00e0nh NULL khi \u0111\u01b0\u1ee3c khai b\u00e1o v\u00e0 n\u00f3 c\u00f3 th\u1ec3 tr\u1ecf \u0111\u1ebfn c\u00e1c v\u1ecb tr\u00ed b\u1ed9 nh\u1edb t\u00f9y \u00fd. N\u1ebfu kh\u00f4ng \u0111\u01b0\u1ee3c g\u00e1n \u0111\u00fang c\u00e1ch, n\u00f3 c\u00f3 th\u1ec3 tr\u1edf th\u00e0nh m\u1ed9t con tr\u1ecf l\u01a1 l\u1eedng khi s\u1eed d\u1ee5ng.<\/p>\n<\/li>\n<li>\n<p>M\u1ed9t con tr\u1ecf \u0111i ra ngo\u00e0i ph\u1ea1m vi, gi\u1ed1ng nh\u01b0 trong tr\u01b0\u1eddng h\u1ee3p h\u00e0m tr\u1ea3 v\u1ec1, khi\u1ebfn con tr\u1ecf tr\u1ecf \u0111\u1ebfn m\u1ed9t v\u1ecb tr\u00ed b\u1ed9 nh\u1edb hi\u1ec7n kh\u00f4ng h\u1ee3p l\u1ec7.<\/p>\n<\/li>\n<\/ol>\n<h2>C\u1ea5u tr\u00fac b\u00ean trong c\u1ee7a con tr\u1ecf l\u01a1 l\u1eedng: C\u00e1ch th\u1ee9c ho\u1ea1t \u0111\u1ed9ng<\/h2>\n<p>Khi m\u1ed9t ch\u01b0\u01a1ng tr\u00ecnh t\u1ea1o m\u1ed9t con tr\u1ecf v\u00e0 c\u1ea5p ph\u00e1t b\u1ed9 nh\u1edb \u0111\u1ed9ng (v\u00ed d\u1ee5: s\u1eed d\u1ee5ng <code data-no-translation=\"\">malloc()<\/code> ho\u1eb7c <code data-no-translation=\"\">new<\/code>), \u0111i\u1ec1u c\u1ea7n thi\u1ebft l\u00e0 ph\u1ea3i theo d\u00f5i b\u1ed9 nh\u1edb \u0111\u00f3 v\u00e0 ph\u00e2n b\u1ed5 n\u00f3 m\u1ed9t c\u00e1ch th\u00edch h\u1ee3p khi kh\u00f4ng c\u00f2n c\u1ea7n thi\u1ebft n\u1eefa. N\u1ebfu m\u1ed9t con tr\u1ecf kh\u00f4ng \u0111\u01b0\u1ee3c c\u1eadp nh\u1eadt ho\u1eb7c \u0111\u1eb7t th\u00e0nh NULL sau khi b\u1ed9 nh\u1edb b\u1ecb gi\u1ea3i ph\u00f3ng, n\u00f3 s\u1ebd ti\u1ebfp t\u1ee5c l\u01b0u \u0111\u1ecba ch\u1ec9 c\u1ee7a b\u1ed9 nh\u1edb \u0111\u01b0\u1ee3c ph\u00e2n b\u1ed5 tr\u01b0\u1edbc \u0111\u00f3, tr\u1edf th\u00e0nh m\u1ed9t con tr\u1ecf l\u01a1 l\u1eedng. Sau \u0111\u00f3, vi\u1ec7c h\u1ee7y tham chi\u1ebfu con tr\u1ecf l\u01a1 l\u1eedng c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn h\u1ecfng d\u1eef li\u1ec7u, treo ch\u01b0\u01a1ng tr\u00ecnh ho\u1eb7c l\u1ed7 h\u1ed5ng b\u1ea3o m\u1eadt.<\/p>\n<h2>Ph\u00e2n t\u00edch c\u00e1c t\u00ednh n\u0103ng ch\u00ednh c\u1ee7a con tr\u1ecf l\u01a1 l\u1eedng<\/h2>\n<p>C\u00e1c t\u00ednh n\u0103ng ch\u00ednh c\u1ee7a con tr\u1ecf l\u01a1 l\u1eedng bao g\u1ed3m:<\/p>\n<ol>\n<li>\n<p><strong>H\u00e0nh vi kh\u00f4ng x\u00e1c \u0111\u1ecbnh<\/strong>: Khi m\u1ed9t ch\u01b0\u01a1ng tr\u00ecnh c\u1ed1 g\u1eafng truy c\u1eadp d\u1eef li\u1ec7u th\u00f4ng qua m\u1ed9t con tr\u1ecf l\u01a1 l\u1eedng, h\u00e0nh vi \u0111\u00f3 s\u1ebd kh\u00f4ng \u0111\u01b0\u1ee3c x\u00e1c \u0111\u1ecbnh v\u00e0 c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn nh\u1eefng k\u1ebft qu\u1ea3 kh\u00f4ng th\u1ec3 \u0111o\u00e1n tr\u01b0\u1edbc.<\/p>\n<\/li>\n<li>\n<p><strong>Kh\u00f3 ph\u00e1t hi\u1ec7n<\/strong>: Vi\u1ec7c x\u00e1c \u0111\u1ecbnh c\u00e1c con tr\u1ecf l\u01a1 l\u1eedng c\u00f3 th\u1ec3 l\u00e0 m\u1ed9t th\u00e1ch th\u1ee9c, \u0111\u1eb7c bi\u1ec7t l\u00e0 trong c\u00e1c c\u01a1 s\u1edf m\u00e3 l\u1edbn. Hi\u1ec7u \u1ee9ng c\u1ee7a ch\u00fang c\u00f3 th\u1ec3 kh\u00f4ng bi\u1ec3u hi\u1ec7n ngay l\u1eadp t\u1ee9c, khi\u1ebfn vi\u1ec7c g\u1ee1 l\u1ed7i tr\u1edf n\u00ean kh\u00f3 kh\u0103n.<\/p>\n<\/li>\n<li>\n<p><strong>R\u1ee7i ro b\u1ea3o m\u1eadt<\/strong>: Khai th\u00e1c con tr\u1ecf l\u01a1 l\u1eedng l\u00e0 m\u1ed9t k\u1ef9 thu\u1eadt ph\u1ed5 bi\u1ebfn trong m\u1ed9t s\u1ed1 lo\u1ea1i t\u1ea5n c\u00f4ng b\u1ea3o m\u1eadt nh\u1ea5t \u0111\u1ecbnh, nh\u01b0 c\u00e1c l\u1ed7 h\u1ed5ng use-after-free.<\/p>\n<\/li>\n<\/ol>\n<h2>C\u00e1c lo\u1ea1i con tr\u1ecf l\u01a1 l\u1eedng<\/h2>\n<p>Con tr\u1ecf l\u01a1 l\u1eedng c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c ph\u00e2n th\u00e0nh nhi\u1ec1u lo\u1ea1i kh\u00e1c nhau d\u1ef1a tr\u00ean nguy\u00ean nh\u00e2n c\u1ee7a ch\u00fang:<\/p>\n<table>\n<thead>\n<tr>\n<th>Ki\u1ec3u<\/th>\n<th>S\u1ef1 mi\u00eau t\u1ea3<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Con tr\u1ecf l\u01a1 l\u1eedng r\u1ed7ng<\/td>\n<td>M\u1ed9t con tr\u1ecf tr\u1ecf \u0111\u1ebfn NULL ho\u1eb7c ch\u01b0a \u0111\u01b0\u1ee3c kh\u1edfi t\u1ea1o.<\/td>\n<\/tr>\n<tr>\n<td>Con tr\u1ecf l\u01a1 l\u1eedng x\u1ebfp ch\u1ed3ng<\/td>\n<td>Con tr\u1ecf tr\u1edf n\u00ean l\u01a1 l\u1eedng sau khi h\u00e0m tr\u1ea3 v\u1ec1.<\/td>\n<\/tr>\n<tr>\n<td>Con tr\u1ecf l\u01a1 l\u1eedng tr\u00ean \u0111\u1ed1ng<\/td>\n<td>Con tr\u1ecf tham chi\u1ebfu b\u1ed9 nh\u1edb \u0111\u00e3 \u0111\u01b0\u1ee3c gi\u1ea3i ph\u00f3ng.<\/td>\n<\/tr>\n<tr>\n<td>Con tr\u1ecf hoang d\u00e3<\/td>\n<td>Con tr\u1ecf ch\u01b0a \u0111\u01b0\u1ee3c kh\u1edfi t\u1ea1o v\u00e0 ch\u1ee9a \u0111\u1ecba ch\u1ec9 t\u00f9y \u00fd.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>C\u00e1ch s\u1eed d\u1ee5ng con tr\u1ecf l\u01a1 l\u1eedng, v\u1ea5n \u0111\u1ec1 v\u00e0 gi\u1ea3i ph\u00e1p<\/h2>\n<p>M\u1eb7c d\u00f9 n\u00f3i chung t\u1ed1t nh\u1ea5t l\u00e0 tr\u00e1nh t\u1ea1o ra c\u00e1c con tr\u1ecf l\u01a1 l\u1eedng, nh\u01b0ng \u0111\u00f4i khi ch\u00fang c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng c\u00f3 ch\u1ee7 \u00fd trong c\u00e1c k\u1ef9 thu\u1eadt l\u1eadp tr\u00ecnh c\u1ee5 th\u1ec3. Tuy nhi\u00ean, \u0111i\u1ec1u n\u00e0y \u0111\u00f2i h\u1ecfi s\u1ef1 hi\u1ec3u bi\u1ebft s\u00e2u s\u1eafc v\u1ec1 c\u00e1ch qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb c\u01a1 b\u1ea3n v\u00e0 ti\u1ec1m \u1ea9n nh\u1eefng r\u1ee7i ro. C\u00e1c v\u1ea5n \u0111\u1ec1 th\u01b0\u1eddng g\u1eb7p li\u00ean quan \u0111\u1ebfn con tr\u1ecf l\u01a1 l\u1eedng bao g\u1ed3m:<\/p>\n<ol>\n<li>\n<p><strong>Tr\u00e0n b\u1ed9 nh\u1edb<\/strong>: Con tr\u1ecf l\u01a1 l\u1eedng c\u00f3 th\u1ec3 l\u00e0m h\u1ecfng b\u1ed9 nh\u1edb, d\u1eabn \u0111\u1ebfn ch\u01b0\u01a1ng tr\u00ecnh kh\u00f4ng \u1ed5n \u0111\u1ecbnh ho\u1eb7c b\u1ecb treo.<\/p>\n<\/li>\n<li>\n<p><strong>L\u1ed7 h\u1ed5ng b\u1ea3o m\u1eadt<\/strong>: Khai th\u00e1c con tr\u1ecf l\u01a1 l\u1eedng l\u00e0 m\u1ed9t chi\u1ebfn thu\u1eadt ph\u1ed5 bi\u1ebfn c\u1ee7a nh\u1eefng k\u1ebb t\u1ea5n c\u00f4ng nh\u1eb1m truy c\u1eadp tr\u00e1i ph\u00e9p v\u00e0o d\u1eef li\u1ec7u nh\u1ea1y c\u1ea3m ho\u1eb7c th\u1ef1c thi m\u00e3 \u0111\u1ed9c.<\/p>\n<\/li>\n<li>\n<p><strong>R\u00f2 r\u1ec9 b\u1ed9 nh\u1edb<\/strong>: Vi\u1ec7c x\u1eed l\u00fd con tr\u1ecf l\u01a1 l\u1eedng kh\u00f4ng \u0111\u00fang c\u00e1ch c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn r\u00f2 r\u1ec9 b\u1ed9 nh\u1edb, khi\u1ebfn b\u1ed9 nh\u1edb \u0111\u01b0\u1ee3c ph\u00e2n b\u1ed5 kh\u00f4ng bao gi\u1edd \u0111\u01b0\u1ee3c gi\u1ea3i ph\u00f3ng, khi\u1ebfn dung l\u01b0\u1ee3ng b\u1ed9 nh\u1edb c\u1ee7a ch\u01b0\u01a1ng tr\u00ecnh t\u0103ng l\u00ean theo th\u1eddi gian.<\/p>\n<\/li>\n<\/ol>\n<p>Gi\u1ea3i ph\u00e1p qu\u1ea3n l\u00fd con tr\u1ecf l\u01a1 l\u1eedng bao g\u1ed3m:<\/p>\n<ul>\n<li>Lu\u00f4n \u0111\u1eb7t con tr\u1ecf th\u00e0nh NULL sau khi gi\u1ea3i ph\u00f3ng b\u1ed9 nh\u1edb \u0111\u1ec3 ng\u0103n ch\u00fang tr\u1edf th\u00e0nh con tr\u1ecf l\u01a1 l\u1eedng.<\/li>\n<li>Tr\u00e1nh s\u1eed d\u1ee5ng con tr\u1ecf v\u01b0\u1ee3t qu\u00e1 ph\u1ea1m vi v\u00e0 tr\u1edf n\u00ean kh\u00f4ng h\u1ee3p l\u1ec7.<\/li>\n<li>S\u1eed d\u1ee5ng con tr\u1ecf th\u00f4ng minh ho\u1eb7c th\u01b0 vi\u1ec7n qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb \u0111\u1ec3 gi\u00fap x\u1eed l\u00fd vi\u1ec7c ph\u00e2n b\u1ed5 b\u1ed9 nh\u1edb m\u1ea1nh m\u1ebd h\u01a1n.<\/li>\n<\/ul>\n<h2>C\u00e1c \u0111\u1eb7c \u0111i\u1ec3m ch\u00ednh v\u00e0 so s\u00e1nh v\u1edbi c\u00e1c thu\u1eadt ng\u1eef t\u01b0\u01a1ng t\u1ef1<\/h2>\n<table>\n<thead>\n<tr>\n<th>Thu\u1eadt ng\u1eef<\/th>\n<th>S\u1ef1 mi\u00eau t\u1ea3<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Con tr\u1ecf l\u01a1 l\u1eedng<\/td>\n<td>M\u1ed9t con tr\u1ecf tr\u1ecf \u0111\u1ebfn b\u1ed9 nh\u1edb \u0111\u00e3 \u0111\u01b0\u1ee3c gi\u1ea3i ph\u00f3ng.<\/td>\n<\/tr>\n<tr>\n<td>Con tr\u1ecf r\u1ed7ng<\/td>\n<td>M\u1ed9t con tr\u1ecf kh\u00f4ng tr\u1ecf \u0111\u1ebfn b\u1ea5t k\u1ef3 v\u1ecb tr\u00ed b\u1ed9 nh\u1edb n\u00e0o.<\/td>\n<\/tr>\n<tr>\n<td>Con tr\u1ecf hoang d\u00e3<\/td>\n<td>M\u1ed9t con tr\u1ecf ch\u1ee9a \u0111\u1ecba ch\u1ec9 t\u00f9y \u00fd v\u00e0 kh\u00f4ng \u0111\u01b0\u1ee3c kh\u1edfi t\u1ea1o.<\/td>\n<\/tr>\n<tr>\n<td>Con tr\u1ecf tr\u1ed1ng<\/td>\n<td>M\u1ed9t lo\u1ea1i con tr\u1ecf chung thi\u1ebfu th\u00f4ng tin v\u1ec1 lo\u1ea1i.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Con tr\u1ecf l\u01a1 l\u1eedng kh\u00e1c v\u1edbi con tr\u1ecf null, con tr\u1ecf hoang d\u00e3 v\u00e0 con tr\u1ecf tr\u1ed1ng trong h\u00e0nh vi v\u00e0 t\u00e1c \u0111\u1ed9ng ti\u1ec1m t\u00e0ng c\u1ee7a ch\u00fang \u0111\u1ed1i v\u1edbi ch\u01b0\u01a1ng tr\u00ecnh. M\u1eb7c d\u00f9 con tr\u1ecf null v\u00e0 con tr\u1ecf void v\u1ed1n kh\u00f4ng ph\u1ea3i l\u00e0 v\u1ea5n \u0111\u1ec1, nh\u01b0ng con tr\u1ecf hoang d\u00e3 v\u00e0 con tr\u1ecf l\u01a1 l\u1eedng c\u00f3 th\u1ec3 d\u1eabn \u0111\u1ebfn c\u00e1c v\u1ea5n \u0111\u1ec1 nghi\u00eam tr\u1ecdng khi x\u1eed l\u00fd sai.<\/p>\n<h2>Quan \u0111i\u1ec3m v\u00e0 c\u00f4ng ngh\u1ec7 t\u01b0\u01a1ng lai li\u00ean quan \u0111\u1ebfn con tr\u1ecf l\u01a1 l\u1eedng<\/h2>\n<p>Vi\u1ec7c qu\u1ea3n l\u00fd con tr\u1ecf v\u00e0 c\u1ea5p ph\u00e1t b\u1ed9 nh\u1edb trong c\u00e1c ng\u00f4n ng\u1eef l\u1eadp tr\u00ecnh hi\u1ec7n \u0111\u1ea1i \u0111\u00e3 ph\u00e1t tri\u1ec3n \u0111\u00e1ng k\u1ec3. C\u00e1c ng\u00f4n ng\u1eef m\u1edbi h\u01a1n nh\u01b0 Java, C# v\u00e0 Python s\u1eed d\u1ee5ng t\u00ednh n\u0103ng qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb t\u1ef1 \u0111\u1ed9ng (thu gom r\u00e1c) ho\u1eb7c c\u01a1 ch\u1ebf x\u1eed l\u00fd con tr\u1ecf an to\u00e0n h\u01a1n, gi\u1ea3m nguy c\u01a1 t\u1ea1o con tr\u1ecf l\u01a1 l\u1eedng.<\/p>\n<p>Tuy nhi\u00ean, trong c\u00e1c \u1ee9ng d\u1ee5ng quan tr\u1ecdng v\u1ec1 hi\u1ec7u n\u0103ng v\u00e0 l\u1eadp tr\u00ecnh h\u1ec7 th\u1ed1ng, C v\u00e0 C++ v\u1eabn \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng r\u1ed9ng r\u00e3i. C\u00e1c nh\u00e0 nghi\u00ean c\u1ee9u v\u00e0 nh\u00e0 ph\u00e1t tri\u1ec3n ng\u00f4n ng\u1eef ti\u1ebfp t\u1ee5c kh\u00e1m ph\u00e1 c\u00e1c gi\u1ea3i ph\u00e1p qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb hi\u1ec7u qu\u1ea3 h\u01a1n v\u00e0 ng\u0103n ng\u1eeba c\u00e1c v\u1ea5n \u0111\u1ec1 nh\u01b0 con tr\u1ecf treo l\u1ee7ng l\u1eb3ng.<\/p>\n<h2>C\u00e1ch s\u1eed d\u1ee5ng ho\u1eb7c li\u00ean k\u1ebft m\u00e1y ch\u1ee7 proxy v\u1edbi con tr\u1ecf l\u01a1 l\u1eedng<\/h2>\n<p>M\u00e1y ch\u1ee7 proxy \u0111\u00f3ng vai tr\u00f2 trung gian gi\u1eefa m\u00e1y kh\u00e1ch v\u00e0 m\u00e1y ch\u1ee7, cung c\u1ea5p nhi\u1ec1u ch\u1ee9c n\u0103ng kh\u00e1c nhau nh\u01b0 b\u1ed9 nh\u1edb \u0111\u1ec7m, l\u1ecdc n\u1ed9i dung v\u00e0 c\u1ea3i ti\u1ebfn b\u1ea3o m\u1eadt. M\u1eb7c d\u00f9 m\u00e1y ch\u1ee7 proxy kh\u00f4ng li\u00ean k\u1ebft tr\u1ef1c ti\u1ebfp v\u1edbi con tr\u1ecf l\u01a1 l\u1eedng nh\u01b0ng ch\u00fang \u0111\u00f3ng m\u1ed9t vai tr\u00f2 quan tr\u1ecdng trong b\u1ea3o m\u1eadt \u1ee9ng d\u1ee5ng web. M\u00e1y ch\u1ee7 proxy c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 tri\u1ec3n khai c\u00e1c bi\u1ec7n ph\u00e1p b\u1ea3o m\u1eadt nh\u1eb1m b\u1ea3o v\u1ec7 kh\u1ecfi c\u00e1c l\u1ed7 h\u1ed5ng ph\u1ed5 bi\u1ebfn, bao g\u1ed3m c\u1ea3 c\u00e1c l\u1ed7 h\u1ed5ng ph\u00e1t sinh t\u1eeb con tr\u1ecf l\u01a1 l\u1eedng v\u00e0 c\u00e1c v\u1ea5n \u0111\u1ec1 kh\u00e1c li\u00ean quan \u0111\u1ebfn b\u1ed9 nh\u1edb.<\/p>\n<h2>Li\u00ean k\u1ebft li\u00ean quan<\/h2>\n<p>\u0110\u1ec3 bi\u1ebft th\u00eam th\u00f4ng tin v\u1ec1 Con tr\u1ecf l\u01a1 l\u1eedng, b\u1ea1n c\u00f3 th\u1ec3 tham kh\u1ea3o c\u00e1c t\u00e0i nguy\u00ean sau:<\/p>\n<ol>\n<li><a href=\"https:\/\/en.cppreference.com\/w\/c\/memory\/dangling\" target=\"_new\" rel=\"noopener nofollow\">Tham kh\u1ea3o C++: Con tr\u1ecf l\u01a1 l\u1eedng<\/a><\/li>\n<li><a href=\"https:\/\/www.geeksforgeeks.org\/understanding-extern-keyword-in-c\/\" target=\"_new\" rel=\"noopener nofollow\">T\u00ecm hi\u1ec3u v\u1ec1 qu\u1ea3n l\u00fd b\u1ed9 nh\u1edb v\u00e0 con tr\u1ecf trong C<\/a><\/li>\n<li><a href=\"https:\/\/www.cprogramming.com\/tutorial\/c\/lesson10.html\" target=\"_new\" rel=\"noopener nofollow\">Nh\u1eefng l\u1ed7i l\u1eadp tr\u00ecnh C th\u01b0\u1eddng g\u1eb7p<\/a><\/li>\n<\/ol>\n<p>H\u00e3y nh\u1edb r\u1eb1ng vi\u1ec7c hi\u1ec3u v\u00e0 qu\u1ea3n l\u00fd c\u00e1c con tr\u1ecf l\u01a1 l\u1eedng l\u00e0 r\u1ea5t quan tr\u1ecdng \u0111\u1ec3 vi\u1ebft ph\u1ea7n m\u1ec1m m\u1ea1nh m\u1ebd v\u00e0 an to\u00e0n. B\u1eb1ng c\u00e1ch x\u1eed l\u00fd c\u1ea9n th\u1eadn vi\u1ec7c ph\u00e2n b\u1ed5 v\u00e0 gi\u1ea3i ph\u00f3ng b\u1ed9 nh\u1edb, c\u00e1c nh\u00e0 ph\u00e1t tri\u1ec3n c\u00f3 th\u1ec3 tr\u00e1nh \u0111\u01b0\u1ee3c nhi\u1ec1u c\u1ea1m b\u1eaby ti\u1ec1m \u1ea9n li\u00ean quan \u0111\u1ebfn con tr\u1ecf l\u01a1 l\u1eedng.<\/p>","protected":false},"featured_media":476586,"menu_order":0,"template":"","meta":{"_acf_changed":false,"content-type":"","inline_featured_image":false,"footnotes":""},"class_list":["post-476585","wiki","type-wiki","status-publish","has-post-thumbnail","hentry"],"acf":{"faq_title":"Frequently Asked Questions about <mark>Dangling Pointer: Understanding the Potential Pitfalls<\/mark>","faq_items":[{"question":"What is a dangling pointer?","answer":"<p>A dangling pointer is a pointer in computer programming that points to a memory location that has been deallocated or freed. When a program attempts to access the memory at that location, it can lead to unexpected and potentially hazardous behavior.<\/p>"},{"question":"How did the concept of dangling pointers originate?","answer":"<p>The concept of dangling pointers emerged with the development of low-level programming languages in the 1970s, particularly in languages like C and C++. The term \"dangling pointer\" was likely coined during the early days of C programming when programmers faced challenges managing memory manually.<\/p>"},{"question":"How does a dangling pointer work internally?","answer":"<p>When memory is deallocated or freed, a pointer that still references the deallocated memory becomes a dangling pointer. If the program attempts to access the memory through the dangling pointer, it can result in undefined behavior, causing data corruption, program crashes, or security vulnerabilities.<\/p>"},{"question":"What are the key features of dangling pointers?","answer":"<p>Key features of dangling pointers include:<\/p><ul><li><strong>Undefined Behavior<\/strong>: Accessing data through a dangling pointer leads to unpredictable outcomes.<\/li><li><strong>Difficult to Detect<\/strong>: Identifying dangling pointers in large codebases can be challenging, making debugging problematic.<\/li><li><strong>Security Risks<\/strong>: Dangling pointers can be exploited in security attacks, such as use-after-free vulnerabilities.<\/li><\/ul>"},{"question":"What types of dangling pointers exist?","answer":"<p>Dangling pointers can be classified into different types based on their causes:<\/p><ul><li><strong>Null Dangling Pointer<\/strong>: A pointer that points to NULL or has not been initialized.<\/li><li><strong>Stack Dangling Pointer<\/strong>: Pointers that become dangling after a function returns.<\/li><li><strong>Heap Dangling Pointer<\/strong>: Pointers that reference deallocated memory.<\/li><li><strong>Wild Pointers<\/strong>: Pointers that have not been initialized and contain arbitrary addresses.<\/li><\/ul>"},{"question":"Can dangling pointers be used intentionally?","answer":"<p>In some specific programming techniques, dangling pointers might be used intentionally. However, it requires a deep understanding of memory management and entails potential risks. Generally, it is best to avoid creating dangling pointers to ensure program stability and security.<\/p>"},{"question":"What problems can be associated with dangling pointers?","answer":"<p>Problems related to dangling pointers include:<\/p><ul><li><strong>Memory Corruption<\/strong>: Dangling pointers can corrupt memory and cause program instability or crashes.<\/li><li><strong>Security Vulnerabilities<\/strong>: Exploiting dangling pointers is a common tactic for attackers to gain unauthorized access to sensitive data or execute malicious code.<\/li><li><strong>Memory Leaks<\/strong>: Mishandling dangling pointers can result in memory leaks, causing the program's memory footprint to grow over time.<\/li><\/ul>"},{"question":"How can developers manage dangling pointers?","answer":"<p>To manage dangling pointers effectively, developers should:<\/p><ul><li>Always set pointers to NULL after deallocating memory to prevent them from becoming dangling pointers.<\/li><li>Avoid using pointers that go out of scope and become invalid.<\/li><li>Use smart pointers or memory management libraries that help in handling memory deallocation more robustly.<\/li><\/ul>"},{"question":"How do proxy servers relate to dangling pointers?","answer":"<p>Proxy servers play a crucial role in web application security. While they are not directly associated with dangling pointers, they can be used to implement security measures that protect against common vulnerabilities, including those arising from memory-related issues.<\/p>"},{"question":"Are there any future technologies related to dangling pointers?","answer":"<p>In modern programming languages, memory management has evolved significantly, with newer languages using automatic memory management or safer pointer handling mechanisms. Researchers and language developers continue to explore solutions to manage memory more efficiently and prevent issues like dangling pointers.<\/p>"}]},"_links":{"self":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/wiki\/476585","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/wiki"}],"about":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/types\/wiki"}],"version-history":[{"count":0,"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/wiki\/476585\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/media\/476586"}],"wp:attachment":[{"href":"https:\/\/oneproxy.pro\/vn\/wp-json\/wp\/v2\/media?parent=476585"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}