[RFC][PATCH] um: Remove proc command from mconsole

Richard Weinberger
2017-05-21T21:19:12Z

This feature is another abuser of set_fs().
Reading proc files from the host side is a debugging feature
with no security checks at all. The path is not sanitized, therefore
any file could be read.
Let's get rid of it.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
Hi!

Unless I miss something is feature is not ABI since it was addeded for
debugging UML only. It is broken wrt. security and abuses set_fs().
I think we can just remove it.

mconsole_proc anyone? ;)

Thanks,
//richard

---

arch/um/drivers/mconsole_kern.c | 52 -----------------------------------------
arch/um/drivers/mconsole_user.c | 1 -
2 files changed, 53 deletions(-)

diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index af326fb6510d..b7fedf77f9f3 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -122,57 +122,6 @@ void mconsole_log(struct mc_request *req)
mconsole_reply(req, "", 0, 0);
}

-void mconsole_proc(struct mc_request *req)
-{
- struct vfsmount *mnt = task_active_pid_ns(current)->proc_mnt;
- char *buf;
- int len;
- struct file *file;
- int first_chunk = 1;
- char *ptr = req->request.data;
-
- ptr += strlen("proc");
- ptr = skip_spaces(ptr);
-
- file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY, 0);
- if (IS_ERR(file)) {
- mconsole_reply(req, "Failed to open file", 1, 0);
- printk(KERN_ERR "open /proc/%s: %ld\n", ptr, PTR_ERR(file));
- goto out;
- }
-
- buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
- if (buf == NULL) {
- mconsole_reply(req, "Failed to allocate buffer", 1, 0);
- goto out_fput;
- }
-
- do {
- loff_t pos = file->f_pos;
- mm_segment_t old_fs = get_fs();
- set_fs(KERNEL_DS);
- len = vfs_read(file, buf, PAGE_SIZE - 1, &pos);
- set_fs(old_fs);
- file->f_pos = pos;
- if (len < 0) {
- mconsole_reply(req, "Read of file failed", 1, 0);
- goto out_free;
- }
- /* Begin the file content on his own line. */
- if (first_chunk) {
- mconsole_reply(req, "\n", 0, 1);
- first_chunk = 0;
- }
- buf[len] = '\0';
- mconsole_reply(req, buf, 0, (len > 0));
- } while (len > 0);
- out_free:
- kfree(buf);
- out_fput:
- fput(file);
- out: ;
-}
-
#define UML_MCONSOLE_HELPTEXT \
"Commands: \n\
version - Get kernel version \n\
@@ -188,7 +137,6 @@ void mconsole_proc(struct mc_request *req)
stop - pause the UML; it will do nothing until it receives a 'go' \n\
go - continue the UML after a 'stop' \n\
log <string> - make UML enter <string> into the kernel log\n\
- proc <file> - returns the contents of the UML's /proc/<file>\n\
stack <pid> - returns the stack of the specified pid\n\
"

diff --git a/arch/um/drivers/mconsole_user.c b/arch/um/drivers/mconsole_user.c
index 99209826adb1..59d81d7ead58 100644
--- a/arch/um/drivers/mconsole_user.c
+++ b/arch/um/drivers/mconsole_user.c
@@ -30,7 +30,6 @@ static struct mconsole_command commands[] = {
{ "stop", mconsole_stop, MCONSOLE_PROC },
{ "go", mconsole_go, MCONSOLE_INTR },
{ "log", mconsole_log, MCONSOLE_INTR },
- { "proc", mconsole_proc, MCONSOLE_PROC },
{ "stack", mconsole_stack, MCONSOLE_INTR },
};

--
2.7.3