The module loader doesn't check for bounds of the ELF section index in
simplify_symbols():
for (i = 1; i < symsec->sh_size / sizeof(Elf_Sym); i++) {
const char *name = info->strtab + sym[i].st_name;
switch (sym[i].st_shndx) {
case SHN_COMMON:
[...]
default:
/* Divert to percpu allocation if a percpu var. */
if (sym[i].st_shndx == info->index.pcpu)
secbase = (unsigned long)mod_percpu(mod);
else
/** HERE --> **/ secbase =
info->sechdrs[sym[i].st_shndx].sh_addr;
sym[i].st_value += secbase;
break;
}
}
A symbol with an out-of-bounds st_shndx value, for example 0xffff
(known as SHN_XINDEX or SHN_HIRESERVE), may cause a kernel panic:
BUG: unable to handle page fault for address: ...
RIP: 0010:simplify_symbols+0x2b2/0x480
...
Kernel panic - not syncing: Fatal exception
This can happen when module ELF is legitimately using SHN_XINDEX or
when it is corrupted.
Add a bounds check in simplify_symbols() to validate that st_shndx is
within the valid range before using it.
This issue was discovered due to a bug in llvm-objcopy, see relevant
discussion for details [1].
[1]
https://lore.kernel.org/linux-modules/[email protected]/
Signed-off-by: Ihor Solodrai <[email protected]>
---
kernel/module/main.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 710ee30b3bea..5bf456fad63e 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1568,6 +1568,13 @@ static int simplify_symbols(struct module *mod, const
struct load_info *info)
break;
default:
+ if (sym[i].st_shndx >= info->hdr->e_shnum) {
+ pr_err("%s: Symbol %s has an invalid section
index %u (max %u)\n",
+ mod->name, name, sym[i].st_shndx,
info->hdr->e_shnum - 1);
+ ret = -ENOEXEC;
+ break;
+ }
+
/* Divert to percpu allocation if a percpu var. */
if (sym[i].st_shndx == info->index.pcpu)
secbase = (unsigned long)mod_percpu(mod);
--
2.52.0
