Update safety documentation for CString::from_ptr and str::from_boxed_utf8_unchecked
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Sky9x
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library/alloc/src/ffi/c_str.rs
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| /// obtained by calling [`CString::into_raw`]. Other usage (e.g., trying to take | ||
| /// ownership of a string that was allocated by foreign code) is likely to lead | ||
| /// to undefined behavior or allocator corruption. | ||
| /// obtained by calling [`CString::into_raw`] and this pointer must not be accessed |
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not the pointer, but the memory it points too
library/alloc/src/str.rs
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| /// | ||
| /// * The provided bytes must contain a valid UTF-8 sequence. | ||
| /// | ||
| /// * The `Box<[u8]>` must have been allocated via the global allocator. |
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This is not a safety requirement. Box<[u8]> is really Box<[u8], Global>, so passing a box with a custom allocator to this function is prevented by type check.
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Yes, you are right. I will fix these.
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tgross35
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tgross35
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CString::from_ptr and str::from_boxed_utf8_unchecked
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Requested reviewer is already assigned to this pull request. Please choose another assignee. |
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You should drop me as a coauthor from the commit message, suggesting a comma in review doesn't mean I had anything to do with authoring this patch :) |
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Done :) @tgross35 |
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Thanks! @bors r+ rollup |
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…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#137439 (Stabilise `std::ffi::c_str`) - rust-lang#137714 (Update safety documentation for `CString::from_ptr` and `str::from_boxed_utf8_unchecked`) - rust-lang#139031 (Use char::is_whitespace directly in str::trim*) - rust-lang#139090 (fix docs for `Peekable::next_if{_eq}`) - rust-lang#140297 (Update example to use CStr::to_string_lossy) - rust-lang#140330 (Clarified bootstrap optimization "true" argument) - rust-lang#140339 (session: Cleanup `CanonicalizedPath::new`) - rust-lang#140346 (rustc_span: Some hygiene cleanups) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#137714 - DiuDiu777:doc-fix, r=tgross35 Update safety documentation for `CString::from_ptr` and `str::from_boxed_utf8_unchecked` ## PR Description This PR addresses missing safety documentation for two APIs: **1. alloc::ffi::CStr::from_raw** - `Alias`: The pointer must not be aliased (accessed via other pointers) during the reconstructed CString's lifetime. - `Owning`: Calling this function twice on the same pointer and creating two objects with overlapping lifetimes, introduces two alive owners of the same memory. This may result in a double-free. - `Dangling`: The prior documentation required the pointer to originate from CString::into_raw, but this constraint is incomplete. A validly sourced pointer can also cause undefined behavior (UB) if it becomes dangling. A simple Poc for this situation: ``` use std::ffi::CString; use std::os::raw::c_char; fn create_dangling() -> *mut c_char { let local_ptr: *mut c_char = { let valid_data = CString::new("valid").unwrap(); valid_data.into_raw() }; unsafe { let _x = CString::from_raw(local_ptr); } local_ptr } fn main() { let dangling = create_dangling(); unsafe {let _y = CString::from_raw(dangling);} // Cause UB! } ``` **2. alloc::str::from_boxed_utf8_unchecked** - `ValidStr`: Bytes must contain a valid UTF-8 sequence.
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PR Description
This PR addresses missing safety documentation for two APIs:
1. alloc::ffi::CStr::from_raw
Alias: The pointer must not be aliased (accessed via other pointers) during the reconstructed CString's lifetime.Owning: Calling this function twice on the same pointer and creating two objects with overlapping lifetimes, introduces two alive owners of the same memory. This may result in a double-free.Dangling: The prior documentation required the pointer to originate from CString::into_raw, but this constraint is incomplete. A validly sourced pointer can also cause undefined behavior (UB) if it becomes dangling. A simple Poc for this situation:2. alloc::str::from_boxed_utf8_unchecked
ValidStr: Bytes must contain a valid UTF-8 sequence.