Calls std::str::from_utf8_unchecked() without any checks

The function xcb::xproto::GetAtomNameReply::name() calls std::str::from_utf8_unchecked() on the raw bytes that were received from the X11 server without any validity checks. The X11 server only prevents interior null bytes, but otherwise allows any X11 client to create an atom for arbitrary bytes.

This issue is tracked here: https://github.com/rust-x-bindings/rust-xcb/issues/96

xcb::xproto::GetPropertyReply::value() allows arbitrary return types

The function xcb::xproto::GetPropertyReply::value() returns a slice of type T where T is an unconstrained type parameter. The raw bytes received from the X11 server are interpreted as the requested type.

The users of the xcb crate are advised to only call this function with the intended types. These are u8, u16, and u32.

This issue is tracked here: https://github.com/rust-x-bindings/rust-xcb/issues/95

Out of bounds read in xcb::xproto::change_property()

xcb::xproto::change_property has (among others) the arguments format: u8 and data: &[T]. The intended use is one of the following cases:

• format = 8 and T = u8
• format = 16 and T = u16
• format = 32 and T = u32 However, this constraint is not enforced. For example, it is possible to call the function with format = 32 and T = u8. In this case, a read beyond the end of the data slice is performed and the bytes are sent to the X11 server.

The users of the xcb crate are advised to only call this function with one of the intended argument combinations.

This issue is tracked here: https://github.com/rust-x-bindings/rust-xcb/issues/94

'Safe' wrapper around std::mem::transmute()

The function xcb::base::cast_event() takes a reference to a xcb::base::GenericEvent and returns a reference to an arbitrary type, as requested by the caller (or found via type interference). The function is implemented as a direct call to std::mem::transmute(). Since the return type is not constrained, this allows transmution to an incorrect type or a type that is larger than the X11 event that was passed in.

X11 events are mostly always 32 bytes large and this function works as intended.

Users are advised to only cast to the event structs provided by the xcb crate (and hope for the best).

This issue is tracked here: https://github.com/rust-x-bindings/rust-xcb/issues/78

On certain platforms, if a user has more than 16 groups, the nix::unistd::getgrouplist function will call the libc getgrouplist function with a length parameter greater than the size of the buffer it provides, resulting in an out-of-bounds write and memory corruption.

The libc getgrouplist function takes an in/out parameter ngroups specifying the size of the group buffer. When the buffer is too small to hold all of the requested user's group memberships, some libc implementations, including glibc and Solaris libc, will modify ngroups to indicate the actual number of groups for the user, in addition to returning an error. The version of nix::unistd::getgrouplist in nix 0.16.0 and up will resize the buffer to twice its size, but will not read or modify the ngroups variable. Thus, if the user has more than twice as many groups as the initial buffer size of 8, the next call to getgrouplist will then write past the end of the buffer.

The issue would require editing /etc/groups to exploit, which is usually only editable by the root user.