[PATCHv4 man-pages 3/3] open.2: describe O_BENEATH flag

From: David Drysdale
Date: Thu Aug 13 2015 - 05:33:12 EST

Signed-off-by: David Drysdale <drysdale@xxxxxxxxxx>
man2/open.2 | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)

diff --git a/man2/open.2 b/man2/open.2
index f49ab3042161..d09511f9ffb0 100644
--- a/man2/open.2
+++ b/man2/open.2
@@ -201,6 +201,43 @@ See
for further details.
See also BUGS, below.
+.B O_BENEATH " (since Linux 4.??)"
+Ensure that the
+.I pathname
+is beneath the current working directory (for
+.BR open (2))
+or the
+.I dirfd
+.BR openat (2)).
+If the
+.I pathname
+is absolute or contains a path component of "..", the
+.BR open ()
+fails with the error
+This occurs even if ".." path component would not actually
+escape the original directory; for example, a
+.I pathname
+of "subdir/../filename" would be rejected.
+Path components that are symbolic links to absolute paths, or that are
+relative paths containing a ".." component, will also cause the
+.BR open ()
+operation to fail with the error
+This feature allows applications to be sure that the opened file is
+within the specified directory, regardless of the original source of the
+.I pathname
+Some security-conscious programs may further ensure
+this by imposing a system call filter (with
+.BR seccomp (2))
+that requires this flag for all
+.BR open ()
+operations, so that the program cannot open files outside of
+specified directories even if subverted.
.BR O_CLOEXEC " (since Linux 2.6.23)"
.\" NOTE! several other man pages refer to this text
Enable the close-on-exec flag for the new file descriptor.
@@ -1015,6 +1052,13 @@ did not match the owner of the file and the caller was not privileged
The operation was prevented by a file seal; see
.BR fcntl (2).
+flag was specified and the
+.I pathname
+was not beneath the relevant directory.
.I pathname
refers to a file on a read-only filesystem and write access was
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