[PATCH 5.15 156/230] module: change to print useful messages from elf_validity_check()

Greg Kroah-Hartman
2022-07-11T09:56:03Z

From: Shuah Khan <skhan@linuxfoundation.org>

[ Upstream commit 7fd982f394c42f25a73fe9dfbf1e6b11fa26b40a ]

elf_validity_check() checks ELF headers for errors and ELF Spec.
compliance and if any of them fail it returns -ENOEXEC from all of
these error paths. Almost all of them don't print any messages.

When elf_validity_check() returns an error, load_module() prints an
error message without error code. It is hard to determine why the
module ELF structure is invalid, even if load_module() prints the
error code which is -ENOEXEC in all of these cases.

Change to print useful error messages from elf_validity_check() to
clearly say what went wrong and why the ELF validity checks failed.

Remove the load_module() error message which is no longer needed.
This patch includes changes to fix build warns on 32-bit platforms:

warning: format '%llu' expects argument of type 'long long unsigned int',
but argument 3 has type 'Elf32_Off' {aka 'unsigned int'}
Reported-by: kernel test robot <lkp@intel.com>

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/module.c | 75 +++++++++++++++++++++++++++++++++++--------------
1 file changed, 54 insertions(+), 21 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 83991c2d5af9..256b3c80a771 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2967,14 +2967,29 @@ static int elf_validity_check(struct load_info *info)
Elf_Shdr *shdr, *strhdr;
int err;

- if (info->len < sizeof(*(info->hdr)))
- return -ENOEXEC;
+ if (info->len < sizeof(*(info->hdr))) {
+ pr_err("Invalid ELF header len %lu\n", info->len);
+ goto no_exec;
+ }

- if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0
- || info->hdr->e_type != ET_REL
- || !elf_check_arch(info->hdr)
- || info->hdr->e_shentsize != sizeof(Elf_Shdr))
- return -ENOEXEC;
+ if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
+ pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
+ goto no_exec;
+ }
+ if (info->hdr->e_type != ET_REL) {
+ pr_err("Invalid ELF header type: %u != %u\n",
+ info->hdr->e_type, ET_REL);
+ goto no_exec;
+ }
+ if (!elf_check_arch(info->hdr)) {
+ pr_err("Invalid architecture in ELF header: %u\n",
+ info->hdr->e_machine);
+ goto no_exec;
+ }
+ if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
+ pr_err("Invalid ELF section header size\n");
+ goto no_exec;
+ }

/*
* e_shnum is 16 bits, and sizeof(Elf_Shdr) is
@@ -2983,8 +2998,10 @@ static int elf_validity_check(struct load_info *info)
*/
if (info->hdr->e_shoff >= info->len
|| (info->hdr->e_shnum * sizeof(Elf_Shdr) >
- info->len - info->hdr->e_shoff))
- return -ENOEXEC;
+ info->len - info->hdr->e_shoff)) {
+ pr_err("Invalid ELF section header overflow\n");
+ goto no_exec;
+ }

info->sechdrs = (void *)info->hdr + info->hdr->e_shoff;

@@ -2992,13 +3009,19 @@ static int elf_validity_check(struct load_info *info)
* Verify if the section name table index is valid.
*/
if (info->hdr->e_shstrndx == SHN_UNDEF
- || info->hdr->e_shstrndx >= info->hdr->e_shnum)
- return -ENOEXEC;
+ || info->hdr->e_shstrndx >= info->hdr->e_shnum) {
+ pr_err("Invalid ELF section name index: %d || e_shstrndx (%d) >= e_shnum (%d)\n",
+ info->hdr->e_shstrndx, info->hdr->e_shstrndx,
+ info->hdr->e_shnum);
+ goto no_exec;
+ }

strhdr = &info->sechdrs[info->hdr->e_shstrndx];
err = validate_section_offset(info, strhdr);
- if (err < 0)
+ if (err < 0) {
+ pr_err("Invalid ELF section hdr(type %u)\n", strhdr->sh_type);
return err;
+ }

/*
* The section name table must be NUL-terminated, as required
@@ -3006,8 +3029,10 @@ static int elf_validity_check(struct load_info *info)
* strings in the section safe.
*/
info->secstrings = (void *)info->hdr + strhdr->sh_offset;
- if (info->secstrings[strhdr->sh_size - 1] != '\0')
- return -ENOEXEC;
+ if (info->secstrings[strhdr->sh_size - 1] != '\0') {
+ pr_err("ELF Spec violation: section name table isn't null terminated\n");
+ goto no_exec;
+ }

/*
* The code assumes that section 0 has a length of zero and
@@ -3015,8 +3040,11 @@ static int elf_validity_check(struct load_info *info)
*/
if (info->sechdrs[0].sh_type != SHT_NULL
|| info->sechdrs[0].sh_size != 0
- || info->sechdrs[0].sh_addr != 0)
- return -ENOEXEC;
+ || info->sechdrs[0].sh_addr != 0) {
+ pr_err("ELF Spec violation: section 0 type(%d)!=SH_NULL or non-zero len or addr\n",
+ info->sechdrs[0].sh_type);
+ goto no_exec;
+ }

for (i = 1; i < info->hdr->e_shnum; i++) {
shdr = &info->sechdrs[i];
@@ -3026,8 +3054,12 @@ static int elf_validity_check(struct load_info *info)
continue;
case SHT_SYMTAB:
if (shdr->sh_link == SHN_UNDEF
- || shdr->sh_link >= info->hdr->e_shnum)
- return -ENOEXEC;
+ || shdr->sh_link >= info->hdr->e_shnum) {
+ pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n",
+ shdr->sh_link, shdr->sh_link,
+ info->hdr->e_shnum);
+ goto no_exec;
+ }
fallthrough;
default:
err = validate_section_offset(info, shdr);
@@ -3049,6 +3081,9 @@ static int elf_validity_check(struct load_info *info)
}

return 0;
+
+no_exec:
+ return -ENOEXEC;
}

#define COPY_CHUNK_SIZE (16*PAGE_SIZE)
@@ -3925,10 +3960,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
* sections.
*/
err = elf_validity_check(info);
- if (err) {
- pr_err("Module has invalid ELF structures\n");
+ if (err)
goto free_copy;
- }

/*
* Everything checks out, so set up the section info
--
2.35.1