OpenBSD unveil(2)

unveil

—

unveil parts of a restricted filesystem view

#include <unistd.h> int
unveil ( const char *path , const char *flags );The first call to unveil removes visibility of the entire filesystem from all other filesystem-related system calls (such asopen(2),chmod(2) andrename(2)), except for the specified path . Subsequent calls to unveil expose additional views of the filesystem.The unveil call is treated specially and can continue to see the filesystem for subsequent calls. unveil can be locked, preventing further filesytem exposure by calling unveil with two NULL arguments.pledge(2) may alternatively be used to remove the "unveil" permission.The flags

argument points to a string consisting of the following characters.

path should be made available for read operations corresponding topledge(2) promise rpath . path should be available for write operations corresponding topledge(2) promise wpath . path should be available for execute operations corresponding topledge(2) promise exec . path should be allowed to be created and removed, corresponding topledge(2) promise cpath . A path that is a directory will enable all filesystem access underneath path using flags if and only if no more specific matching unveil () exists at a lower level.Attempts to access paths not allowed by unveil will result in an error of EACCES when the flags argument does not match the attempted operation. ENOENT is returned for paths for which no unveil flags are present.As withpledge(2), the use of unveil () in an application will require lots of study and understanding of the interfaces called. In most cases it is best practice to unveil the directories in which an application makes use of files. It is important to consider that directory results are remembered at the time of a call to unveil (). This means that a directory that is removed and recreated after a call to unveil () will appear to not exist. Non directories are remembered by name within their containing directory, and so may be created, removed, or re-created after a call to unveil () and still appear to exist. unveil

() returns 0 on success or -1 on failure.

E2BIG The addition of path would exceed the per-process limit for pledged paths. ENOENT A directory in path did not exist. EINVAL An invalid value of flags was used. EPERM An attempt to add permission to flags was made, or path was not accessible, or unveil was called after it was locked The unveil

() system call first appeared in

OpenBSD 6.4

.