Resolving Stack Overflow Errors With Safe-PDF Crate In Rust

October 7, 2025 by StackCamp Team 60 views

Stack Overflow During PDF Processing with Safe-PDF Crate

Hey guys! Today, we're diving into a tricky issue: a stack overflow error encountered while processing a PDF file using the safe-pdf crate in Rust. Stack overflows can be super frustrating, but don't worry, we'll break it down and figure out what's going on and how to fix it. Let's get started!

Understanding the Problem

So, what exactly is a stack overflow? In simple terms, it's like having a whiteboard that you keep writing on, but you never erase anything. Eventually, you run out of space, and that's what happens with the stack in your program. The stack is a region of memory used for function calls and local variables. When a function calls itself repeatedly (or calls other functions that call it back), it keeps adding data to the stack. If this goes on for too long without stopping, the stack overflows, leading to a crash. This is especially common in recursive functions that don't have a proper base case to stop the recursion.

The Stack Overflow Error

In this specific scenario, we're encountering a stack-overflow error while using the safe-pdf crate to parse a PDF file. Here's the error message we're seeing:

AddressSanitizer:DEADLYSIGNAL
=================================================================
==46613==ERROR: AddressSanitizer: stack-overflow on address 0x7ffc81bf9d38 (pc 0x55ea29009067 bp 0x7ffc81bfa5a0 sp 0x7ffc81bf9d40 T0)
    #0 0x55ea29009067 in MemcmpInterceptorCommon(void*, int (*)(void const*, void const*, unsigned long), void const*, void const*, unsigned long) /rustc/llvm/src/llvm-project/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:869:16
    #1 0x55ea290098dc in memcmp /rustc/llvm/src/llvm-project/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:880:10
    #2 0x55ea29180186 in _$LT$A$u20$as$u20$core..slice..cmp..SliceOrd$GT$::compare::h13d4073ab3320b29 /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/cmp.rs:328:34
    #3 0x55ea29180186 in core::slice::cmp::_$LT$impl$u20$core..cmp..Ord$u20$for$u20$u5b$T$u5d$GT$::cmp::h99943a3ed1fdec0a /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/cmp.rs:33:9
    #4 0x55ea29180186 in core::str::traits::_$LT$impl$u20$core..cmp..Ord$u20$for$u20$str$GT$::cmp::h8d34aa59b7782adb /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/str/traits.rs:21:25
    #5 0x55ea29180186 in alloc::collections::btree::search::_$LT$impl$u20$alloc..collections..btree..node..NodeRef$LT$BorrowType$C$K$C$V$C$Type$GT$GT$::find_key_index::hb5011264726247af /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/collections/btree/search.rs:226:23
    #6 0x55ea29180186 in alloc::collections::btree::search::_$LT$impl$u20$alloc..collections..btree..node..NodeRef$LT$BorrowType$C$K$C$V$C$Type$GT$GT$::search_node::h33731047eb200149 /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/collections/btree/search.rs:203:29
    #7 0x55ea29180186 in alloc::collections::btree::search::_$LT$impl$u20$alloc..collections..btree..node..NodeRef$LT$BorrowType$C$K$C$V$C$alloc..collections..btree..node..marker..LeafOrInternal$GT$GT$::search_tree::hd0ff6e4e40ee2b37 /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/collections/btree/search.rs:58:31
    #8 0x55ea29180186 in alloc::collections::btree::map::BTreeMap$LT$K$C$V$C$A$GT$::get::hbfc3c6f223422cc5 /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/collections/btree/map.rs:724:25
    #9 0x55ea291779dc in pdf_object::dictionary::Dictionary::get::h2bfce98c4b9db7a7 /home/runner/.cargo/git/checkouts/safe-pdf-0f2b1e222030fb0d/cb8dbf2/crates/pdf-object/src/dictionary.rs:22:25
    #10 0x55ea291779dc in pdf_object::dictionary::Dictionary::get_or_err::heaaa33fee7c63932 /home/runner/.cargo/git/checkouts/safe-pdf-0f2b1e222030fb0d/cb8dbf2/crates/pdf-object/src/dictionary.rs:32:14
    #11 0x55ea290bc674 in _$LT$pdf_page..pages..PdfPages$u20$as$u20$pdf_object..traits..FromDictionary$GT$::from_dictionary::h248cb7abb72ba90d /home/runner/.cargo/git/checkouts/safe-pdf-0f2b1e222030fb0d/cb8dbf2/crates/pdf-page/src/pages.rs:46:37
    #12 0x55ea290bcc3d in _$LT$pdf_page..pages..PdfPages$u20$as$u20$pdf_object..traits..FromDictionary$GT$::from_dictionary::h248cb7abb72ba90d /home/runner/.cargo/git/checkouts/safe-pdf-0f2b1e222030fb0d/cb8dbf2/crates/pdf-page/src/pages.rs:71:37
    #13 0x55ea290bcc3d in 

...

    #252 0x55ea290bcc3d in _$LT$pdf_page..pages..PdfPages$u20$as$u20$pdf_object..traits..FromDictionary$GT$::from_dictionary::h248cb7abb72ba90d /home/runner/.cargo/git/checkouts/safe-pdf-0f2b1e222030fb0d/cb8dbf2/crates/pdf-page/src/pages.rs:71:37
    #253 0x55ea290bcc3d in _$LT$pdf_page..pages..PdfPages$u20$as$u20$pdf_object..traits..FromDictionary$GT$::from_dictionary::h248cb7abb72ba90d /home/runner/.cargo/git/checkouts/safe-pdf-0f2b1e222030fb0d/cb8dbf2/crates/pdf-page/src/pages.rs:71:37

SUMMARY: AddressSanitizer: stack-overflow /home/runner/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/cmp.rs:328:34 in _$LT$A$u20$as$u20$core..slice..cmp..SliceOrd$GT$::compare::h13d4073ab3320b29
==46613==ABORTING

The error log points to a recursive call within the pdf_page::pages::PdfPages struct's from_dictionary method. This suggests that the PDF file's structure might be causing the parser to enter an infinite recursion, ultimately overflowing the stack. The key parts of the stack trace to notice are the repeated calls to _$LT$pdf_page..pages..PdfPages$u20$as$u20$pdf_object..traits..FromDictionary$GT$::from_dictionary and the mention of alloc::collections::btree::map::BTreeMap$LT$K$C$V$C$A$GT$::get, which indicates that the issue likely involves the parsing of dictionaries within the PDF structure.

The Code Snippet

Here’s the Rust code snippet that triggers the error:

use std::fs;
use safe_pdf::document::PdfDocument;

fn check_file(file_path: &str) {
    match fs::read(file_path) {
        Ok(bytes) => {
            if let Err(e) = PdfDocument::from(&bytes) {
                eprintln!("Error {}", e);
            }
        }
        Err(e) => eprintln!("Error {}", e),
    }
}

This code reads a PDF file from the specified path and attempts to parse it using PdfDocument::from(&bytes). If an error occurs during parsing, it prints the error message. Pretty straightforward, right? But sometimes, simple code can hide complex issues.

The Malformed PDF File

The provided PDF file is quite minimal, but it contains the basic structure of a PDF:

%PDF-1.4
%
1 0 obj<</Pages 2 0 R>>endobj
2 0 obj<</Type/Pages/Kids[2 0 R]>>endobj
trailer<</Root 1 0 R>>startxref
4%%EOF

Notice anything fishy? The issue lies in the circular reference in the /Kids array of the Pages object (object 2). It refers to itself (2 0 R), creating an infinite loop when the parser tries to traverse the page tree. This is a classic example of a malformed PDF that can cause parsers to choke.

Diagnosing the Stack Overflow

To really nail down why this stack overflow is happening, let's dig deeper into the call stack. The error message gives us a breadcrumb trail to follow, specifically highlighting the from_dictionary function within the pdf-page crate and the BTreeMap::get function. Here’s a breakdown of what's likely happening:

PdfDocument::from(&bytes): This is where the parsing process begins. The safe-pdf crate starts to interpret the PDF structure.
pdf_page::pages::PdfPages::from_dictionary: This function is responsible for parsing the pages tree within the PDF. It extracts information about pages and their relationships from a dictionary object.
Recursive Calls: The from_dictionary function likely encounters the /Kids array, which points back to the same object (2 0 R). This creates a recursive loop, where the function keeps calling itself to parse the same page object over and over again.
BTreeMap::get: This function is used to look up entries in a dictionary. The recursive calls to from_dictionary lead to repeated lookups in the BTreeMap, further contributing to the stack growth.
Stack Overflow: Eventually, the stack runs out of space due to the unbounded recursion, and the program crashes with a stack overflow error.

To confirm this diagnosis, you can use debugging tools like gdb or lldb to step through the code and observe the call stack. This will give you a real-time view of the function calls and help you pinpoint the exact location of the infinite recursion.

Solutions and Strategies

Now that we understand the root cause, let’s explore some strategies to tackle this stack overflow. There are several approaches we can take, ranging from simple workarounds to more robust solutions.

1. Check and Sanitize the PDF:

One of the most effective ways to prevent stack overflows caused by malformed PDFs is to validate and sanitize the file before processing it. Guys, this involves checking the PDF's structure for inconsistencies, circular references, and other potential issues. You can use third-party libraries or tools specifically designed for PDF validation. By ensuring that the PDF adheres to the standard, you can prevent many parsing errors, including stack overflows. This is especially important when dealing with PDFs from untrusted sources.

2. Increase Stack Size (Temporary Fix):

While it's not a permanent solution, increasing the stack size can temporarily alleviate the stack overflow issue. You can do this by setting the ulimit -s command in your shell before running the program. However, be cautious because increasing the stack size too much can lead to other problems, such as memory exhaustion. This approach is more of a band-aid than a real fix, as it doesn't address the underlying issue of infinite recursion.

3. Limit Recursion Depth:

To prevent infinite recursion, you can introduce a limit on the recursion depth. This involves adding a counter to the recursive function and stopping the recursion when the counter exceeds a certain threshold. For instance, in the from_dictionary function, you can add a parameter that tracks the depth of recursion. If the depth exceeds a predefined limit, the function can return an error or a default value, thus preventing the stack overflow. This method ensures that the parsing process doesn't get stuck in an infinite loop, making it a more robust solution.

4. Use Iterative Approach Instead of Recursion:

One of the most effective ways to avoid stack overflows is to replace recursion with iteration. Iterative algorithms use loops instead of function calls, which means they don't add to the stack. You can refactor the from_dictionary function to use a loop to traverse the pages tree. This often involves using a data structure like a queue or a stack (not the call stack!) to keep track of the nodes to visit. By using an iterative approach, you can process even deeply nested PDF structures without running the risk of a stack overflow. Plus, iterative solutions are often more memory-efficient in the long run.

5. Report the Issue to the `safe-pdf` Crate Maintainers:

If you've identified a bug in the safe-pdf crate that causes a stack overflow, it's a good idea to report the issue to the crate maintainers. Providing them with a minimal reproducible example (like the PDF file in this case) can help them fix the bug in the crate itself. This not only benefits you but also helps improve the crate for other users. Open-source projects thrive on community contributions, and reporting issues is a valuable way to give back.

Implementing a Solution: Limiting Recursion Depth

Let's walk through a practical example of how to limit recursion depth. This approach is a good balance between simplicity and effectiveness. We'll modify the check_file function to include a maximum recursion depth and pass it to a modified version of the PdfDocument::from function (which we'll assume exists for the sake of this example).

First, let’s add a helper function that limits the recursion depth:

use std::fs;
use safe_pdf::document::PdfDocument;

fn check_file(file_path: &str) {
    match fs::read(file_path) {
        Ok(bytes) => {
            let max_recursion_depth = 100; // Set a reasonable limit
            match PdfDocument::from_bytes(&bytes, max_recursion_depth) {
                Ok(_) => println!("PDF parsed successfully!"),
                Err(e) => eprintln!("Error: {}", e),
            }
        }
        Err(e) => eprintln!("Error: {}", e),
    }
}

In this example, we've added max_recursion_depth and passed it to PdfDocument::from_bytes. Now, let's outline how you might modify the safe-pdf crate (if you were contributing to it) to actually use this limit. (Note: This is a conceptual modification and not actual code from the crate.)

Inside the PdfDocument::from_bytes (or similar) function, you would pass this max_recursion_depth to the recursive function, let's say from_dictionary. The from_dictionary function might look something like this:

fn from_dictionary(dict: &Dictionary, current_depth: usize, max_depth: usize) -> Result<PdfPages, Error> {
    if current_depth > max_depth {
        return Err(Error::RecursionLimitExceeded);
    }

    // ... parsing logic ...

    // Recursive call (example)
    let kids = dict.get("/Kids")
                   .and_then(|obj| obj.as_array())
                   .ok_or(Error::InvalidDictionary)?;

    for kid in kids {
        if let Some(kid_dict) = kid.as_dictionary() {
            from_dictionary(kid_dict, current_depth + 1, max_depth)?;
        }
    }

    Ok(PdfPages { /* ... */ })
}

Here, we've added current_depth to track the current recursion level and max_depth as the limit. At the beginning of the function, we check if current_depth exceeds max_depth. If it does, we return an error, preventing further recursion. In the recursive call, we increment current_depth. This ensures that the recursion stops when it hits the limit.

Conclusion

Stack overflows can be tricky, but understanding the root cause is half the battle. In this case, a malformed PDF with a circular reference led to infinite recursion. By implementing strategies like input validation, recursion limits, and iterative approaches, we can prevent these issues. And remember, contributing to open-source projects by reporting bugs helps everyone in the community. Keep coding, and stay safe from those stack overflows! You got this!