2020-09-02 06:47:34

by Qu Wenruo

Subject: [PATCH] module: Add more error message for failed kernel module loading

When kernel module loading failed, user space only get one of the
following error messages:

- ENOEXEC
This is the most confusing one. From corrupted ELF header to bad
WRITE|EXEC flags check introduced by in module_enforce_rwx_sections()
all returns this error number.

- EPERM
This is for blacklisted modules. But mod doesn't do extra explain
on this error either.

- ENOMEM
The only error which needs no explain.

This means, if a user got "Exec format error" from modprobe, it provides
no meaningful way for the user to debug, and will take extra time
communicating to get extra info.

So this patch will add extra error messages for -ENOEXEC and -EPERM
errors, allowing user to do better debugging and reporting.

Signed-off-by: Qu Wenruo <[email protected]>
Reviewed-by: Lucas De Marchi <[email protected]>
---
Changelog:
v2:
- Add extra section description for the error message of
module_enforce_rwx_sections()
- Add Reviewed-by tags.
---
kernel/module.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 1c5cff34d9f2..2c00059ac1c9 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2096,8 +2096,11 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
int i;

for (i = 0; i < hdr->e_shnum; i++) {
- if ((sechdrs[i].sh_flags & shf_wx) == shf_wx)
+ if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) {
+ pr_err("%s: section %s (index %d) has invalid WRITE|EXEC flags\n",
+ mod->name, secstrings + sechdrs[i].sh_name, i);
return -ENOEXEC;
+ }
}

return 0;
@@ -3825,8 +3828,10 @@ static int load_module(struct load_info *info, const char __user *uargs,
char *after_dashes;

err = elf_header_check(info);
- if (err)
+ if (err) {
+ pr_err("Module has invalid ELF header\n");
goto free_copy;
+ }

err = setup_load_info(info, flags);
if (err)
@@ -3834,6 +3839,7 @@ static int load_module(struct load_info *info, const char __user *uargs,

if (blacklisted(info->name)) {
err = -EPERM;
+ pr_err("Module %s is blacklisted\n", info->name);
goto free_copy;
}

--
2.28.0

2020-09-02 09:41:59

by Jessica Yu

Subject: Re: [PATCH] module: Add more error message for failed kernel module loading

+++ Qu Wenruo [02/09/20 14:46 +0800]:
>When kernel module loading failed, user space only get one of the
>following error messages:
>
>- ENOEXEC
> This is the most confusing one. From corrupted ELF header to bad
> WRITE|EXEC flags check introduced by in module_enforce_rwx_sections()
> all returns this error number.
>
>- EPERM
> This is for blacklisted modules. But mod doesn't do extra explain
> on this error either.
>
>- ENOMEM
> The only error which needs no explain.
>
>This means, if a user got "Exec format error" from modprobe, it provides
>no meaningful way for the user to debug, and will take extra time
>communicating to get extra info.
>
>So this patch will add extra error messages for -ENOEXEC and -EPERM
>errors, allowing user to do better debugging and reporting.
>
>Signed-off-by: Qu Wenruo <[email protected]>
>Reviewed-by: Lucas De Marchi <[email protected]>

Applied, thanks.

Jessica