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link_elf: fix SysV hash function overflow

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Quoting from https://maskray.me/blog/2023-04-12-elf-hash-function:

The System V Application Binary Interface (generic ABI) specifies the
ELF object file format. When producing an output executable or shared
object needing a dynamic symbol table (.dynsym), a linker generates a
.hash section with type SHT_HASH to hold a symbol hash table. A DT_HASH
tag is produced to hold the address of .hash.

The function is supposed to return a value no larger than 0x0fffffff.
Unfortunately, there is a bug. When unsigned long consists of more than
32 bits, the return value may be larger than UINT32_MAX. For instance,
elf_hash((const unsigned char *)"\xff\x0f\x0f\x0f\x0f\x0f\x12") returns
0x100000002, which is clearly unintended, as the function should behave
the same way regardless of whether long represents a 32-bit integer or
a 64-bit integer.

Reviewed by:	kib, Fangrui Song
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D39517
This commit is contained in:
Ed Maste 2023-04-12 10:04:27 -04:00
parent e1ff83fb19
commit 2ef2c26f3f
1 changed files with 8 additions and 11 deletions
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19
sys/kern/link_elf.c
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@ -1470,23 +1470,20 @@ relocate_file(elf_file_t ef)
}
/*
* Hash function for symbol table lookup. Don't even think about changing
* this. It is specified by the System V ABI.
* SysV hash function for symbol table lookup. It is specified by the
* System V ABI.
*/
static unsigned long
static Elf32_Word
elf_hash(const char *name)
{
const unsigned char *p = (const unsigned char *) name;
unsigned long h = 0;
unsigned long g;
const unsigned char *p = (const unsigned char *)name;
Elf32_Word h = 0;
while (*p != '\0') {
h = (h << 4) + *p++;
if ((g = h & 0xf0000000) != 0)
h ^= g >> 24;
h &= ~g;
h ^= (h >> 24) & 0xf0;
}
return (h);
return (h & 0x0fffffff);
}
static int
@ -1497,7 +1494,7 @@ link_elf_lookup_symbol1(linker_file_t lf, const char *name, c_linker_sym_t *sym,
unsigned long symnum;
const Elf_Sym* symp;
const char *strp;
unsigned long hash;
Elf32_Word hash;
/* If we don't have a hash, bail. */
if (ef->buckets == NULL || ef->nbuckets == 0) {