mirror of
https://github.com/RGBCube/serenity
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23a7ccf607
This is a preparation before we can create a usable mechanism to use filesystem-specific mount flags. To keep some compatibility with userland code, LibC and LibCore mount functions are kept being usable, but now instead of doing an "atomic" syscall, they do multiple syscalls to perform the complete procedure of mounting a filesystem. The FileBackedFileSystem IntrusiveList in the VFS code is now changed to be protected by a Mutex, because when we mount a new filesystem, we need to check if a filesystem is already created for a given source_fd so we do a scan for that OpenFileDescription in that list. If we fail to find an already-created filesystem we create a new one and register it in the list if we successfully mounted it. We use a Mutex because we might need to initiate disk access during the filesystem creation, which will take other mutexes in other parts of the kernel, therefore making it not possible to take a spinlock while doing this.
76 lines
3.8 KiB
Markdown
76 lines
3.8 KiB
Markdown
## Name
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pledge - reduce process capabilities
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## Synopsis
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```**c++
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#include <unistd.h>
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int pledge(const char* promises, const char* execpromises);
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```
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## Description
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`pledge()` makes a promise to the kernel that from this moment on, the calling process will only use a subset of system functionality.
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Functionality is divided into a curated set of promises (described below), which can be combined to cover the program's needs. Both arguments are space-separated lists of promises.
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Note that `pledge()` can be called repeatedly to remove previously-pledged promises, but it can never regain capabilities once lost.
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`promises` are applied to the current process, and will also be inherited by children created by [`fork`(2)](help://man/2/fork).
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`execpromises` are applied if/when a new process image is created with [`exec`(2)](help://man/2/exec).
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If `promises` or `execpromises` is null, the corresponding value is unchanged.
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If the process later attempts to use any system functionality it has previously promised *not* to use, the process is instantly terminated. Note that a process that has not ever called `pledge()` is considered to not have made any promises, and is allowed use any system functionality (subject to regular permission checks).
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`pledge()` is intended to be used in programs that want to sandbox themselves, either to limit the impact of a possible vulnerability exploitation, or before intentionally executing untrusted code.
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## Promises
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* `stdio`: Basic I/O, memory allocation, information about self, various non-destructive syscalls
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* `thread`: The POSIX threading API (\*)
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* `id`: Ability to change UID/GID
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* `tty`: TTY related functionality
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* `proc`: Process and scheduling related functionality
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* `exec`: The [`exec`(2)](help://man/2/exec) syscall
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* `unix`: UNIX local domain sockets
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* `inet`: IPv4 domain sockets
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* `accept`: May use [`accept`(2)](help://man/2/accept) to accept incoming socket connections on already listening sockets (\*)
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* `rpath`: "Read" filesystem access
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* `wpath`: "Write" filesystem access
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* `cpath`: "Create" filesystem access
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* `dpath`: Creating new device files
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* `chown`: Changing file owner/group
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* `fattr`: Changing file attributes/permissions
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* `video`: May use [`ioctl`(2)](help://man/2/ioctl) and [`mmap`(2)](help://man/2/mmap) on framebuffer video devices
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* `settime`: Changing the system time and date
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* `setkeymap`: Changing the system keyboard layout (\*)
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* `sigaction`: Change signal handlers and dispositions (\*)
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* `sendfd`: Send file descriptors over a local socket
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* `recvfd`: Receive file descriptors over a local socket
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* `ptrace`: The [`ptrace`(2)](help://man/2/ptrace) syscall (\*)
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* `prot_exec`: [`mmap`(2)](help://man/2/mmap) and [`mprotect`(2)](help://man/2/mprotect) with `PROT_EXEC`
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* `map_fixed`: [`mmap`(2)](help://man/2/mmap) with `MAP_FIXED` or `MAP_FIXED_NOREPLACE` (\*)
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* `mount`: [`mount`(2)](help://man/2/mount) Various filesystem mount related syscalls (\*)
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* `no_error`: Ignore requests of pledge elevation going forwards, this is useful for enforcing _execpromises_ while the child process wants to ask for more upfront (Note that the elevation requests are _not_ granted, merely ignored), this is similar to the `error` pledge in OpenBSD.
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* `jail`: Various jail-specific syscalls (\*)
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Promises marked with an asterisk (\*) are SerenityOS specific extensions not supported by the original OpenBSD `pledge()`.
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## Errors
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* `EFAULT`: `promises` and/or `execpromises` are not null and not in readable memory.
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* `EINVAL`: One or more invalid promises were specified.
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* `EPERM`: An attempt to increase capabilities was rejected.
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## History
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The `pledge()` system call was first introduced by OpenBSD. The implementation in SerenityOS differs in many ways and is by no means final.
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## See also
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* [`unveil`(2)](help://man/2/unveil)
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* [`Mitigations`(7)](help://man/7/Mitigations)
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