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head/lib/libc/sys/open.2
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | ||||
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | ||||
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | ||||
.\" SUCH DAMAGE. | .\" SUCH DAMAGE. | ||||
.\" | .\" | ||||
.\" @(#)open.2 8.2 (Berkeley) 11/16/93 | .\" @(#)open.2 8.2 (Berkeley) 11/16/93 | ||||
.\" $FreeBSD$ | .\" $FreeBSD$ | ||||
.\" | .\" | ||||
.Dd October 20, 2018 | .Dd November 11, 2018 | ||||
.Dt OPEN 2 | .Dt OPEN 2 | ||||
.Os | .Os | ||||
.Sh NAME | .Sh NAME | ||||
.Nm open , openat | .Nm open , openat | ||||
.Nd open or create a file for reading, writing or executing | .Nd open or create a file for reading, writing or executing | ||||
.Sh LIBRARY | .Sh LIBRARY | ||||
.Lb libc | .Lb libc | ||||
.Sh SYNOPSIS | .Sh SYNOPSIS | ||||
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.Xr umask 2 ) . | .Xr umask 2 ) . | ||||
.Pp | .Pp | ||||
The | The | ||||
.Fn openat | .Fn openat | ||||
function is equivalent to the | function is equivalent to the | ||||
.Fn open | .Fn open | ||||
function except in the case where the | function except in the case where the | ||||
.Fa path | .Fa path | ||||
specifies a relative path. | specifies a relative path, or the | ||||
In this case the file to be opened is determined relative to the directory | .Dv O_BENEATH | ||||
flag is provided. | |||||
For | |||||
.Fn openat | |||||
and relative | |||||
.Fa path , | |||||
the file to be opened is determined relative to the directory | |||||
associated with the file descriptor | associated with the file descriptor | ||||
.Fa fd | .Fa fd | ||||
instead of the current working directory. | instead of the current working directory. | ||||
The | The | ||||
.Fa flag | .Fa flag | ||||
parameter and the optional fourth parameter correspond exactly to | parameter and the optional fourth parameter correspond exactly to | ||||
the parameters of | the parameters of | ||||
.Fn open . | .Fn open . | ||||
If | If | ||||
.Fn openat | .Fn openat | ||||
is passed the special value | is passed the special value | ||||
.Dv AT_FDCWD | .Dv AT_FDCWD | ||||
in the | in the | ||||
.Fa fd | .Fa fd | ||||
parameter, the current working directory is used | parameter, the current working directory is used | ||||
and the behavior is identical to a call to | and the behavior is identical to a call to | ||||
.Fn open . | .Fn open . | ||||
.Pp | .Pp | ||||
When | |||||
.Fn openat | |||||
is called with an absolute | |||||
.Fa path | |||||
without the | |||||
.Dv O_BENEATH | |||||
flag, it ignores the | |||||
.Fa fd | |||||
argument. | |||||
When | |||||
.Dv O_BENEATH | |||||
is specified with an absolute | |||||
.Fa path , | |||||
a directory passed by the | |||||
.Fa fd | |||||
argument is used as the topping point for the resolution. | |||||
See the definition of the | |||||
.Dv O_BENEATH | |||||
flag below. | |||||
.Pp | |||||
In | In | ||||
.Xr capsicum 4 | .Xr capsicum 4 | ||||
capability mode, | capability mode, | ||||
.Fn open | .Fn open | ||||
is not permitted. | is not permitted. | ||||
The | The | ||||
.Fa path | .Fa path | ||||
argument to | argument to | ||||
.Fn openat | .Fn openat | ||||
must be strictly relative to a file descriptor | must be strictly relative to a file descriptor | ||||
.Fa fd , | .Fa fd , | ||||
as defined in | as defined in | ||||
.Pa sys/kern/vfs_lookup.c . | .Pa sys/kern/vfs_lookup.c . | ||||
.Fa path | .Fa path | ||||
must not be an absolute path and must not contain ".." components. | must not be an absolute path and must not contain ".." components | ||||
which cause the path resolution to escape the directory hierarchy | |||||
starting at | |||||
.Fa fd . | |||||
Additionally, no symbolic link in | Additionally, no symbolic link in | ||||
.Fa path | .Fa path | ||||
may contain ".." components either. | may target absolute path or contain escaping ".." components. | ||||
.Fa fd | .Fa fd | ||||
must not be | must not be | ||||
.Dv AT_FDCWD . | .Dv AT_FDCWD . | ||||
.Pp | .Pp | ||||
If the | |||||
.Dv vfs.lookup_cap_dotdot | |||||
.Xr sysctl 3 | |||||
MIB is set to zero, ".." components in the paths, | |||||
used in capability mode, or with the | |||||
.Dv O_BENEATH | |||||
flag, are completely disabled. | |||||
If the | |||||
.Dv vfs.lookup_cap_dotdot_nonlocal | |||||
MIB is set to zero, ".." is not allowed if found on non-local filesystem. | |||||
.Pp | |||||
The flags specified are formed by | The flags specified are formed by | ||||
.Em or Ns 'ing | .Em or Ns 'ing | ||||
the following values | the following values | ||||
.Pp | .Pp | ||||
.Bd -literal -offset indent -compact | .Bd -literal -offset indent -compact | ||||
O_RDONLY open for reading only | O_RDONLY open for reading only | ||||
O_WRONLY open for writing only | O_WRONLY open for writing only | ||||
O_RDWR open for reading and writing | O_RDWR open for reading and writing | ||||
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O_FSYNC synchronous writes | O_FSYNC synchronous writes | ||||
O_SYNC synchronous writes | O_SYNC synchronous writes | ||||
O_NOFOLLOW do not follow symlinks | O_NOFOLLOW do not follow symlinks | ||||
O_NOCTTY ignored | O_NOCTTY ignored | ||||
O_TTY_INIT ignored | O_TTY_INIT ignored | ||||
O_DIRECTORY error if file is not a directory | O_DIRECTORY error if file is not a directory | ||||
O_CLOEXEC set FD_CLOEXEC upon open | O_CLOEXEC set FD_CLOEXEC upon open | ||||
O_VERIFY verify the contents of the file | O_VERIFY verify the contents of the file | ||||
O_BENEATH require path to be strictly relative to starting directory | O_BENEATH require path to be strictly relative to topping directory | ||||
.Ed | .Ed | ||||
.Pp | .Pp | ||||
Opening a file with | Opening a file with | ||||
.Dv O_APPEND | .Dv O_APPEND | ||||
set causes each write on the file | set causes each write on the file | ||||
to be appended to the end. | to be appended to the end. | ||||
If | If | ||||
.Dv O_TRUNC | .Dv O_TRUNC | ||||
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.Dq verified | .Dq verified | ||||
means is implementation specific. | means is implementation specific. | ||||
The run-time linker (rtld) uses this flag to ensure shared objects have | The run-time linker (rtld) uses this flag to ensure shared objects have | ||||
been verified before operating on them. | been verified before operating on them. | ||||
.Pp | .Pp | ||||
.Dv O_BENEATH | .Dv O_BENEATH | ||||
returns | returns | ||||
.Er ENOTCAPABLE | .Er ENOTCAPABLE | ||||
if the specified path, after resolving all symlinks and ".." references | if the specified relative path, after resolving all symlinks and ".." | ||||
in it, does not reside in the directory hierarchy of children beneath | references, does not reside in the directory hierarchy of | ||||
the starting directory, or is an absolute path. | children beneath the topping directory. | ||||
Starting directory is the process current directory if relative | Topping directory is the process current directory if relative | ||||
.Fa path | .Fa path | ||||
is used for | is used for | ||||
.Fn open , | .Fn open , | ||||
and the directory referenced by the | and the directory referenced by the | ||||
.Fa fd | .Fa fd | ||||
argument when specifying relative | argument when using | ||||
.Fa path | |||||
for | |||||
.Fn openat . | .Fn openat . | ||||
If the specified path is absolute, | |||||
.Dv O_BENEATH | |||||
allows arbitrary prefix that ends up at the topping directory, | |||||
after which all further resolved components must be under it. | |||||
.Pp | .Pp | ||||
If successful, | If successful, | ||||
.Fn open | .Fn open | ||||
returns a non-negative integer, termed a file descriptor. | returns a non-negative integer, termed a file descriptor. | ||||
It returns \-1 on failure. | It returns \-1 on failure. | ||||
The file pointer used to mark the current position within the | The file pointer used to mark the current position within the | ||||
file is set to the beginning of the file. | file is set to the beginning of the file. | ||||
.Pp | .Pp | ||||
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.Fn open | .Fn open | ||||
was called and the process is in capability mode. | was called and the process is in capability mode. | ||||
.It Bq Er ENOTCAPABLE | .It Bq Er ENOTCAPABLE | ||||
.Fa path | .Fa path | ||||
is an absolute path, | is an absolute path, | ||||
or contained a ".." component leading to a | or contained a ".." component leading to a | ||||
directory outside of the directory hierarchy specified by | directory outside of the directory hierarchy specified by | ||||
.Fa fd , | .Fa fd , | ||||
and the process is in capability mode or the | and the process is in capability mode. | ||||
.It Bq Er ENOTCAPABLE | |||||
The | |||||
.Dv O_BENEATH | .Dv O_BENEATH | ||||
flag was provided. | flag was provided, and the absolute | ||||
.Fa path | |||||
does not have its tail fully contained under the topping directory, | |||||
or the relative | |||||
.Fa path | |||||
escapes it. | |||||
.El | .El | ||||
.Sh SEE ALSO | .Sh SEE ALSO | ||||
.Xr chmod 2 , | .Xr chmod 2 , | ||||
.Xr close 2 , | .Xr close 2 , | ||||
.Xr dup 2 , | .Xr dup 2 , | ||||
.Xr fexecve 2 , | .Xr fexecve 2 , | ||||
.Xr fhopen 2 , | .Xr fhopen 2 , | ||||
.Xr getdtablesize 2 , | .Xr getdtablesize 2 , | ||||
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