CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS
Percentile
9.5%
When using rustix::fs::Dir
using the linux_raw
backend, it’s possible for the iterator to “get stuck” when an IO error is encountered. Combined with a memory over-allocation issue in rustix::fs::Dir::read_more
, this can cause quick and unbounded memory explosion (gigabytes in a few seconds if used on a hot path) and eventually lead to an OOM crash of the application.
The symptoms were initially discovered in https://github.com/imsnif/bandwhich/issues/284. That post has lots of details of our investigation. See this post and the Discord thread for details.
This issue is caused by the combination of two independent bugs:
rustix::fs::Dir
iterator can fail to halt after encountering an IO error, causing the caller to be stuck in an infinite loop.Dir::read_more
incorrectly grows the read buffer unconditionally each time it is called, regardless of necessity.Since <Dir as Iterator>::next
calls Dir::read
, which in turn calls Dir::read_more
, this means an IO error encountered during reading a directory can lead to rapid and unbounded growth of memory use.
fn main() -> Result<(), Box<dyn std::error::Error>> {
// create a directory, get a FD to it, then unlink the directory but keep the FD
std::fs::create_dir("tmp_dir")?;
let dir_fd = rustix::fs::openat(
rustix::fs::CWD,
rustix::cstr!("tmp_dir"),
rustix::fs::OFlags::RDONLY | rustix::fs::OFlags::CLOEXEC,
rustix::fs::Mode::empty(),
)?;
std::fs::remove_dir("tmp_dir")?;
// iterator gets stuck in infinite loop and memory explodes
rustix::fs::Dir::read_from(dir_fd)?
// the iterator keeps returning `Some(Err(_))`, but never halts by returning `None`
// therefore if the implementation ignores the error (or otherwise continues
// after seeing the error instead of breaking), the loop will not halt
.filter_map(|dirent_maybe_error| dirent_maybe_error.ok())
.for_each(|dirent| {
// your happy path
println!("{dirent:?}");
});
Ok(())
}
If a program tries to access a directory with its file descriptor after the file has been unlinked (or any other action that leaves the Dir
iterator in the stuck state), and the implementation does not break after seeing an error, it can cause a memory explosion.
As an example, Linux’s various virtual file systems (e.g. /proc
, /sys
) can contain directories that spontaneously pop in and out of existence. Attempting to iterate over them using rustix::fs::Dir
directly or indirectly (e.g. with the procfs
crate) can trigger this fault condition if the implementation decides to continue on errors.
An attacker knowledgeable about the implementation details of a vulnerable target can therefore try to trigger this fault condition via any one or a combination of several available APIs. If successful, the application host will quickly run out of memory, after which the application will likely be terminated by an OOM killer, leading to denial of service.
discord.com/channels/273534239310479360/1161137828395237556
github.com/advisories/GHSA-c827-hfw6-qwvm
github.com/bytecodealliance/rustix/commit/31fd98ca723b93cc6101a3e29843ea5cf094e159
github.com/bytecodealliance/rustix/commit/87481a97f4364d12d5d6f30cdd025a0fc509b8ec
github.com/bytecodealliance/rustix/commit/df3c3a192cf144af0da8a57417fb4addbdc611f6
github.com/bytecodealliance/rustix/commit/eecece4a84fc58eafdc809cc2cedd374dee876a5
github.com/bytecodealliance/rustix/security/advisories/GHSA-c827-hfw6-qwvm
github.com/imsnif/bandwhich/issues/284
github.com/imsnif/bandwhich/issues/284#issuecomment-1754321993
nvd.nist.gov/vuln/detail/CVE-2024-43806