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age-core: Reject invalid last lines in AgeStanza bodies

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The length of a Base64 encoding can never be 1 mod 4, because that
only provides six of the eight bits necessary for encoding a byte.
Previously we checked that every line was valid Base64 (which works
because all lines except the last are 64 characters, which exactly
encodes 48 bytes).

In 0.7.0 we improved the parser efficiency by only running the Base64
decoder lazily. We replaced the per-line check with an `is_base64_char`
check, but forgot to reject the invalid subset of last-line lengths.
This commit is contained in:
Jack Grigg 2021-12-23 20:40:25 +00:00
parent 349b4c31cb
commit 8da15148fc
1 changed files with 12 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

17
age-core/src/format.rs
View file

@ -134,7 +134,7 @@ pub mod read {
branch::alt,
bytes::streaming::{tag, take_while1, take_while_m_n},
character::streaming::newline,
combinator::{map, map_opt, opt},
combinator::{map, map_opt, opt, verify},
multi::{many_till, separated_list1},
sequence::{pair, preceded, terminated},
IResult,
@ -169,8 +169,12 @@ pub mod read {
many_till(
// Any body lines before the last MUST be full-length.
terminated(take_while_m_n(64, 64, is_base64_char), newline),
// Last body line MUST be short (empty if necessary).
terminated(take_while_m_n(0, 63, is_base64_char), newline),
// Last body line MUST be short (empty if necessary), and MUST be a valid
// Base64 length (i.e. the length must not be 1 mod 4).
verify(
terminated(take_while_m_n(0, 63, is_base64_char), newline),
|line: &[u8]| line.len() % 4 != 1,
),
),
|(full_chunks, partial_chunk): (Vec<&[u8]>, &[u8])| {
let mut chunks = full_chunks;
@ -185,9 +189,12 @@ pub mod read {
separated_list1(newline, take_while1(is_base64_char)),
|chunks: Vec<&[u8]>| {
// Enforce that the only chunk allowed to be shorter than 64 characters
// is the last chunk.
// is the last chunk, and that its length must not be 1 mod 4.
let (partial_chunk, full_chunks) = chunks.split_last().unwrap();
if full_chunks.iter().any(|s| s.len() != 64) || partial_chunk.len() > 64 {
if full_chunks.iter().any(|s| s.len() != 64)
|| partial_chunk.len() > 64
|| partial_chunk.len() % 4 == 1
{
None
} else {
Some(chunks)