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openat - The openat(2) system call is used to open a file relative to a directory file descriptor.


openat(2) performs the same task as open(2): it opens the file pathname (relative to the directory referred to by the file descriptor dirfd), but it can optionally provide the additional functionality of AT_SYMLINK_NOFOLLOW.

The arguments are similar to open(2): the pathname of the file to be opened, a flags flags and a mode mode to set it if it is created. The only difference is that the dirfd argument is a file descriptor of the directory that will serve as a prefix of the pathname. This allows openat(2) to be used in a thread-safe sequence of operations that all operate relative to the same directory.


  • dirfd: int[K] - A file descriptor referring to the directory relative to which pathname is to be accessed. If dirfd is the special value AT_FDCWD, then pathname is relative to the current working directory.
  • pathname: const char*[K,U] - A pathname of the file to be opened.
  • flags: int[K] -File access mode and file status flags. This argument is a bit-mask created by ORing together the O_RDONLY, O_WRONLY, O_RDWR, O_APPEND, O_CREAT, O_EXCL, O_NOCTTY, O_TRUNC, O_DSYNC, O_DIRECTORY, O_NOFOLLOW, O_SYMLINK, O_CLOEXEC and O_NONBLOCK flags.
  • mode: mode_t[K] -Mode of the created file. This argument must be supplied when O_CREAT is specified in flags.

Available Tags

  • K - Originated from kernel-space.
  • U - Originated from user space (for example, pointer to user space memory used to get it)
  • TOCTOU - Vulnerable to TOCTOU (time of check, time of use)
  • OPT - Optional argument - might not always be available (passed with null value)






Hooked to analyze the system call parameters.

Example Use Case

openat() can be used to open a file in a secure manner, given that two file descriptors are available. The intention of openat() is that it can be used in a thread-safe sequence of operations that all operate relative to the same directory. A simple example of this is ensuring that a file is opened in the same directory as its parent, and not in another directory, even if the working directory has been changed in the meantime.


Due to the fact that openat() uses an internal buffer to store the pathname, there is a potential vulnerability to TOCTOU (time of check, time of use) attacks.

creat(2), open(2), stat(2)

This document was automatically generated by OpenAI and needs review. It might not be accurate and might contain errors. The authors of Tracee recommend that the user reads the "events.go" source file to understand the events and their arguments better.