[musl] realloc buffer overflow issue

[Benedict <hymeng90@126.com>]

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I found an memory leak issue in my multi-thread, which had fixed issue by the following patch



https://git.musl-libc.org/cgit/musl/commit/src/malloc?id=3e16313f8fe2ed143ae0267fd79d63014c24779f






about this patch, I think it involved a bug for realloc function: when the request size 'n' (the second paramter passed to realloc) lesser than the original memory size 'n0' (the memory block that first paramter of realloc pointed to) and the next chunk of  'self ' is in used state, the realloc should call trim(self, n) to split current chunk rather than call malloc, that will cause memcpy buffer overflow due to 'n < n0', and it will cause next malloc crash...


after fix, I think it should be like:
lock(mal.split_merge_lock);


size_t nsize = next->csize & C_INUSE ? 0 : CHUNK_SIZE(next);
if (nsize)) {
int i = bin_index(nsize);
lock_bin(i);
if (!(next->csize & C_INUSE)) {
unbin(next, i);
next = NEXT_CHUNK(next);
self->csize = next->psize = n0+nsize | C_INUSE;
}
unlock_bin(i);
}
    
    if(CHUNK_SIZE(self) >= n) {
        trim(self, n);
        unlock(mal.split_merge_lock);
return CHUNK_TO_MEM(self);
    }
unlock(mal.split_merge_lock);


copy_realloc:
/* As a last resort, allocate a new chunk and copy to it. */
new = malloc(n-OVERHEAD);
if (!new) return 0;
copy_free_ret:
memcpy(new, p, n0-OVERHEAD);
free(CHUNK_TO_MEM(self));
return new;




Benedict

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