execve: use 'struct filename *' for executable name passing

This changes 'do_execve()' to get the executable name as a 'struct
filename', and to free it when it is done.  This is what the normal
users want, and it simplifies and streamlines their error handling.

The controlled lifetime of the executable name also fixes a
use-after-free problem with the trace_sched_process_exec tracepoint: the
lifetime of the passed-in string for kernel users was not at all
obvious, and the user-mode helper code used UMH_WAIT_EXEC to serialize
the pathname allocation lifetime with the execve() having finished,
which in turn meant that the trace point that happened after
mm_release() of the old process VM ended up using already free'd memory.

To solve the kernel string lifetime issue, this simply introduces
"getname_kernel()" that works like the normal user-space getname()
function, except with the source coming from kernel memory.

As Oleg points out, this also means that we could drop the tcomm[] array
from 'struct linux_binprm', since the pathname lifetime now covers
setup_new_exec().  That would be a separate cleanup.

Reported-by: Igor Zhbanov <i.zhbanov@samsung.com>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 3 insertions, 2 deletions

diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index fd8bf3219ef7..b4a745d7d9a9 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -115,7 +115,6 @@ extern int copy_strings_kernel(int argc, const char *const *argv,
 extern int prepare_bprm_creds(struct linux_binprm *bprm);
 extern void install_exec_creds(struct linux_binprm *bprm);
 extern void set_binfmt(struct linux_binfmt *new);
-extern void free_bprm(struct linux_binprm *);
 extern ssize_t read_code(struct file *, unsigned long, loff_t, size_t);
 
 #endif /* _LINUX_BINFMTS_H */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 09f553c59813..d79678c188ad 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2079,6 +2079,7 @@ extern struct file * dentry_open(const struct path *, int, const struct cred *);
 extern int filp_close(struct file *, fl_owner_t id);
 
 extern struct filename *getname(const char __user *);
+extern struct filename *getname_kernel(const char *);
 
 enum {
 	FILE_CREATED = 1,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 68a0e84463a0..a781dec1cd0b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -128,6 +128,7 @@ struct bio_list;
 struct fs_struct;
 struct perf_event_context;
 struct blk_plug;
+struct filename;
 
 /*
  * List of flags we want to share for kernel threads,
@@ -2311,7 +2312,7 @@ extern void do_group_exit(int);
 extern int allow_signal(int);
 extern int disallow_signal(int);
 
-extern int do_execve(const char *,
+extern int do_execve(struct filename *,
 		     const char __user * const __user *,
 		     const char __user * const __user *);
 extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);