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570b8b8836
The pair_chunk() function is provided as an easy helper for parsing
chunks that just want a pointer to a set of bytes. But every caller has
a hidden bug: because we return only the pointer without the matching
chunk size, the callers have no clue how many bytes they are allowed to
look at. And as a result, they may read off the end of the mmap'd data
when the on-disk file does not match their expectations.
Since chunk files are typically used for local-repository data like
commit-graph files and midx's, the security implications here are pretty
mild. The worst that can happen is that you hand somebody a corrupted
repository tarball, and running Git on it does an out-of-bounds read and
crashes. So it's worth being more defensive, but we don't need to drop
everything and fix every caller immediately.
I noticed the problem because the pair_chunk_fn() callback does not look
at its chunk_size argument, and wanted to annotate it to silence
-Wunused-parameter. We could do that now, but we'd lose the hint that
this code should be audited and fixed.
So instead, let's set ourselves up for going down that path:
1. Provide a pair_chunk() function that does return the size, which
prepares us for fixing these cases.
2. Rename the existing function to pair_chunk_unsafe(). That gives us
an easy way to grep for cases which still need to be fixed, and the
name should cause anybody adding new calls to think twice before
using it.
There are no callers of the "safe" version yet, but we'll add some in
subsequent patches.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
86 lines
2.5 KiB
C
86 lines
2.5 KiB
C
#ifndef CHUNK_FORMAT_H
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#define CHUNK_FORMAT_H
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#include "hash-ll.h"
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struct hashfile;
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struct chunkfile;
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#define CHUNK_TOC_ENTRY_SIZE (sizeof(uint32_t) + sizeof(uint64_t))
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/*
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* Initialize a 'struct chunkfile' for writing _or_ reading a file
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* with the chunk format.
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*
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* If writing a file, supply a non-NULL 'struct hashfile *' that will
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* be used to write.
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*
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* If reading a file, use a NULL 'struct hashfile *' and then call
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* read_table_of_contents(). Supply the memory-mapped data to the
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* pair_chunk() or read_chunk() methods, as appropriate.
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*
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* DO NOT MIX THESE MODES. Use different 'struct chunkfile' instances
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* for reading and writing.
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*/
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struct chunkfile *init_chunkfile(struct hashfile *f);
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void free_chunkfile(struct chunkfile *cf);
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int get_num_chunks(struct chunkfile *cf);
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typedef int (*chunk_write_fn)(struct hashfile *f, void *data);
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void add_chunk(struct chunkfile *cf,
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uint32_t id,
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size_t size,
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chunk_write_fn fn);
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int write_chunkfile(struct chunkfile *cf, void *data);
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int read_table_of_contents(struct chunkfile *cf,
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const unsigned char *mfile,
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size_t mfile_size,
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uint64_t toc_offset,
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int toc_length);
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#define CHUNK_NOT_FOUND (-2)
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/*
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* Find 'chunk_id' in the given chunkfile and assign the
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* given pointer to the position in the mmap'd file where
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* that chunk begins. Likewise the "size" parameter is filled
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* with the size of the chunk.
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*
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* Returns CHUNK_NOT_FOUND if the chunk does not exist.
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*/
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int pair_chunk(struct chunkfile *cf,
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uint32_t chunk_id,
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const unsigned char **p,
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size_t *size);
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/*
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* Unsafe version of pair_chunk; it does not return the size,
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* meaning that the caller cannot possibly be careful about
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* reading out of bounds from the mapped memory.
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*
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* No new callers should use this function, and old callers should
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* be audited and migrated over to using the regular pair_chunk()
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* function.
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*/
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int pair_chunk_unsafe(struct chunkfile *cf,
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uint32_t chunk_id,
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const unsigned char **p);
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typedef int (*chunk_read_fn)(const unsigned char *chunk_start,
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size_t chunk_size, void *data);
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/*
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* Find 'chunk_id' in the given chunkfile and call the
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* given chunk_read_fn method with the information for
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* that chunk.
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*
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* Returns CHUNK_NOT_FOUND if the chunk does not exist.
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*/
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int read_chunk(struct chunkfile *cf,
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uint32_t chunk_id,
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chunk_read_fn fn,
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void *data);
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uint8_t oid_version(const struct git_hash_algo *algop);
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#endif
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