Re: [PATCH AUTOSEL for 4.9 188/293] fs: warn in case userspace lied about modprobe return

[Luis R. Rodriguez]

On Sun, Apr 8, 2018 at 5:25 PM, Sasha Levin
 wrote:
> From: "Luis R. Rodriguez" 
>
> [ Upstream commit 41124db869b7e00e12052555f8987867ac01d70c ]
>
> kmod <= v19 was broken -- it could return 0 to modprobe calls,
> incorrectly assuming that a kernel module was built-in, whereas in
> reality the module was just forming in the kernel. The reason for this
> is an incorrect userspace heuristics. A userspace kmod fix is available
> for it [0], however should userspace break again we could go on with
> an failed get_fs_type() which is hard to debug as the request_module()
> is detected as returning 0. The first suspect would be that there is
> something worth with the kernel's module loader and obviously in this
> case that is not the issue.
>
> Since these issues are painful to debug complain when we know userspace
> has outright lied to us.
>
> [0] 
> http://git.kernel.org/cgit/utils/kernel/kmod/kmod.git/commit/libkmod/libkmod-module.c?id=fd44a98ae2eb5eb32161088954ab21e58e19dfc4
>
> Suggested-by: Rusty Russell 
> Cc: Jessica Yu 
> Signed-off-by: Luis R. Rodriguez 
> Signed-off-by: Al Viro 
> Signed-off-by: Sasha Levin 

Acked-by: Luis R. Rodriguez 

The issue is real, and specially older kernels with older userspace
can suffer with pain. It doesn't follow the typical stable
candidate-fix, however, such simple check *can* help rule out tons of
stupid debugging where the culprit really was userspace.

 Luis

Re: [PATCH AUTOSEL for 4.9 188/293] fs: warn in case userspace lied about modprobe return

[Luis R. Rodriguez]

On Sun, Apr 8, 2018 at 5:25 PM, Sasha Levin
 wrote:
> From: "Luis R. Rodriguez" 
>
> [ Upstream commit 41124db869b7e00e12052555f8987867ac01d70c ]
>
> kmod <= v19 was broken -- it could return 0 to modprobe calls,
> incorrectly assuming that a kernel module was built-in, whereas in
> reality the module was just forming in the kernel. The reason for this
> is an incorrect userspace heuristics. A userspace kmod fix is available
> for it [0], however should userspace break again we could go on with
> an failed get_fs_type() which is hard to debug as the request_module()
> is detected as returning 0. The first suspect would be that there is
> something worth with the kernel's module loader and obviously in this
> case that is not the issue.
>
> Since these issues are painful to debug complain when we know userspace
> has outright lied to us.
>
> [0] 
> http://git.kernel.org/cgit/utils/kernel/kmod/kmod.git/commit/libkmod/libkmod-module.c?id=fd44a98ae2eb5eb32161088954ab21e58e19dfc4
>
> Suggested-by: Rusty Russell 
> Cc: Jessica Yu 
> Signed-off-by: Luis R. Rodriguez 
> Signed-off-by: Al Viro 
> Signed-off-by: Sasha Levin 

Acked-by: Luis R. Rodriguez 

The issue is real, and specially older kernels with older userspace
can suffer with pain. It doesn't follow the typical stable
candidate-fix, however, such simple check *can* help rule out tons of
stupid debugging where the culprit really was userspace.

 Luis

[PATCH AUTOSEL for 4.9 188/293] fs: warn in case userspace lied about modprobe return

[Sasha Levin]

From: "Luis R. Rodriguez" 

[ Upstream commit 41124db869b7e00e12052555f8987867ac01d70c ]

kmod <= v19 was broken -- it could return 0 to modprobe calls,
incorrectly assuming that a kernel module was built-in, whereas in
reality the module was just forming in the kernel. The reason for this
is an incorrect userspace heuristics. A userspace kmod fix is available
for it [0], however should userspace break again we could go on with
an failed get_fs_type() which is hard to debug as the request_module()
is detected as returning 0. The first suspect would be that there is
something worth with the kernel's module loader and obviously in this
case that is not the issue.

Since these issues are painful to debug complain when we know userspace
has outright lied to us.

[0] 
http://git.kernel.org/cgit/utils/kernel/kmod/kmod.git/commit/libkmod/libkmod-module.c?id=fd44a98ae2eb5eb32161088954ab21e58e19dfc4

Suggested-by: Rusty Russell 
Cc: Jessica Yu 
Signed-off-by: Luis R. Rodriguez 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin 
---
 fs/filesystems.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index c5618db110be..cd7ba6301a60 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -275,8 +275,10 @@ struct file_system_type *get_fs_type(const char *name)
int len = dot ? dot - name : strlen(name);
 
fs = __get_fs_type(name, len);
-   if (!fs && (request_module("fs-%.*s", len, name) == 0))
+   if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
fs = __get_fs_type(name, len);
+   WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no 
fs?\n", len, name);
+   }
 
if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
put_filesystem(fs);
-- 
2.15.1

[PATCH AUTOSEL for 4.9 188/293] fs: warn in case userspace lied about modprobe return

[Sasha Levin]

From: "Luis R. Rodriguez" 

[ Upstream commit 41124db869b7e00e12052555f8987867ac01d70c ]

kmod <= v19 was broken -- it could return 0 to modprobe calls,
incorrectly assuming that a kernel module was built-in, whereas in
reality the module was just forming in the kernel. The reason for this
is an incorrect userspace heuristics. A userspace kmod fix is available
for it [0], however should userspace break again we could go on with
an failed get_fs_type() which is hard to debug as the request_module()
is detected as returning 0. The first suspect would be that there is
something worth with the kernel's module loader and obviously in this
case that is not the issue.

Since these issues are painful to debug complain when we know userspace
has outright lied to us.

[0] 
http://git.kernel.org/cgit/utils/kernel/kmod/kmod.git/commit/libkmod/libkmod-module.c?id=fd44a98ae2eb5eb32161088954ab21e58e19dfc4

Suggested-by: Rusty Russell 
Cc: Jessica Yu 
Signed-off-by: Luis R. Rodriguez 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin 
---
 fs/filesystems.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index c5618db110be..cd7ba6301a60 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -275,8 +275,10 @@ struct file_system_type *get_fs_type(const char *name)
int len = dot ? dot - name : strlen(name);
 
fs = __get_fs_type(name, len);
-   if (!fs && (request_module("fs-%.*s", len, name) == 0))
+   if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
fs = __get_fs_type(name, len);
+   WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no 
fs?\n", len, name);
+   }
 
if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
put_filesystem(fs);
-- 
2.15.1