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fix: ELF note section parsing alignment and name length comparison #109

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fix: ELF note section parsing alignment and name length comparison #109

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46b4fe7
fix: ELF note section parsing alignment and name length comparison
KoHaRxnP Aug 5, 2026
76339f8
fix: ELF note section parsing alignment and name length comparison
KoHaRxnP Aug 5, 2026
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26 changes: 17 additions & 9 deletions postject-api.h
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Original file line number Diff line number Diff line change
Expand Up @@ -130,6 +130,8 @@ static const void* postject_find_resource(
size_t n = main_program_info.dlpi_phnum;
uintptr_t base_addr = main_program_info.dlpi_addr;

size_t name_len = strlen(name);

// iterate program header
for (; n > 0; n--, p += sizeof(ElfW(Phdr))) {
ElfW(Phdr)* phdr = (ElfW(Phdr)*)p;
Expand All @@ -139,6 +141,10 @@ static const void* postject_find_resource(
continue;
}

// Determine alignment for notes in this segment (default to ELF class word size if p_align is 0/1)
size_t align = phdr->p_align > 0 ? phdr->p_align : sizeof(ElfW(Addr));
if (align < 4) align = 4; // ELF Note standard minimum alignment is usually 4

// note segment starts at base address + segment virtual address
uintptr_t pos = (base_addr + phdr->p_vaddr);
uintptr_t end = (pos + phdr->p_memsz);
Expand All @@ -150,18 +156,20 @@ static const void* postject_find_resource(
}

ElfW(Nhdr)* note = (ElfW(Nhdr)*)(uintptr_t)pos;

// Calculate padded offsets dynamically based on segment alignment
size_t namesz_padded = roundup(note->n_namesz, align);
size_t descsz_padded = roundup(note->n_descsz, align);

if (note->n_namesz != 0 && note->n_descsz != 0 &&
strncmp((char*)(pos + sizeof(ElfW(Nhdr))), (char*)name,
sizeof(name)) == 0) {
note->n_namesz >= name_len &&
strncmp((char*)(pos + sizeof(ElfW(Nhdr))), (char*)name, name_len) == 0) {
*size = note->n_descsz;
// advance past note header and aligned name
// to get to description data
return (void*)((uintptr_t)note + sizeof(ElfW(Nhdr)) +
roundup(note->n_namesz, 4));
// advance past note header and aligned name to get to description data
return (void*)((uintptr_t)note + sizeof(ElfW(Nhdr)) + namesz_padded);
}

pos += (sizeof(ElfW(Nhdr)) + roundup(note->n_namesz, 4) +
roundup(note->n_descsz, 4));
pos += (sizeof(ElfW(Nhdr)) + namesz_padded + descsz_padded);
}
}
return NULL;
Expand Down Expand Up @@ -206,4 +214,4 @@ static const void* postject_find_resource(
#endif
}

#endif // POSTJECT_API_H_
#endif // POSTJECT_API_H_
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