| Message ID | 20210812084348.6521-3-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove in-tree usage of MAP_DENYWRITE | expand |
On Thu, Aug 12, 2021 at 10:43:43AM +0200, David Hildenbrand wrote: > Let's factor the main logic out into atomic_set_mm_exe_file(), such that > all mm->exe_file logic is contained in kernel/fork.c. > > While at it, perform some simple cleanups that are possible now that > we're simplifying the individual functions. > > Signed-off-by: David Hildenbrand <david@redhat.com> > --- Looks good. Acked-by: Christian Brauner <christian.brauner@ubuntu.com> > include/linux/mm.h | 2 ++ > kernel/fork.c | 35 +++++++++++++++++++++++++++++++++-- > kernel/sys.c | 33 +-------------------------------- > 3 files changed, 36 insertions(+), 34 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 7ca22e6e694a..197505324b74 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2581,6 +2581,8 @@ extern int mm_take_all_locks(struct mm_struct *mm); > extern void mm_drop_all_locks(struct mm_struct *mm); > > extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file); > +extern int atomic_set_mm_exe_file(struct mm_struct *mm, > + struct file *new_exe_file); > extern struct file *get_mm_exe_file(struct mm_struct *mm); > extern struct file *get_task_exe_file(struct task_struct *task); > > diff --git a/kernel/fork.c b/kernel/fork.c > index bc94b2cc5995..6bd2e52bcdfb 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1149,8 +1149,8 @@ void mmput_async(struct mm_struct *mm) > * Main users are mmput() and sys_execve(). Callers prevent concurrent > * invocations: in mmput() nobody alive left, in execve task is single > * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the > - * mm->exe_file, but does so without using set_mm_exe_file() in order > - * to avoid the need for any locks. > + * mm->exe_file, but uses atomic_set_mm_exe_file(), avoiding the need > + * for any locks. > */ > void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) > { > @@ -1170,6 +1170,37 @@ void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) > fput(old_exe_file); > } > > +int atomic_set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) > +{ > + struct vm_area_struct *vma; > + struct file *old_exe_file; > + int ret = 0; > + > + /* Forbid mm->exe_file change if old file still mapped. */ > + old_exe_file = get_mm_exe_file(mm); > + if (old_exe_file) { > + mmap_read_lock(mm); > + for (vma = mm->mmap; vma && !ret; vma = vma->vm_next) { > + if (!vma->vm_file) > + continue; > + if (path_equal(&vma->vm_file->f_path, > + &old_exe_file->f_path)) > + ret = -EBUSY; > + } > + mmap_read_unlock(mm); > + fput(old_exe_file); > + if (ret) > + return ret; > + } > + > + /* set the new file, lockless */ > + get_file(new_exe_file); > + old_exe_file = xchg(&mm->exe_file, new_exe_file); > + if (old_exe_file) > + fput(old_exe_file); > + return 0; > +} > + > /** > * get_mm_exe_file - acquire a reference to the mm's executable file > * > diff --git a/kernel/sys.c b/kernel/sys.c > index ef1a78f5d71c..40551b411fda 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1846,7 +1846,6 @@ SYSCALL_DEFINE1(umask, int, mask) > static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) > { > struct fd exe; > - struct file *old_exe, *exe_file; > struct inode *inode; > int err; > > @@ -1869,40 +1868,10 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) > if (err) > goto exit; > > - /* > - * Forbid mm->exe_file change if old file still mapped. > - */ > - exe_file = get_mm_exe_file(mm); > - err = -EBUSY; > - if (exe_file) { > - struct vm_area_struct *vma; > - > - mmap_read_lock(mm); > - for (vma = mm->mmap; vma; vma = vma->vm_next) { > - if (!vma->vm_file) > - continue; > - if (path_equal(&vma->vm_file->f_path, > - &exe_file->f_path)) > - goto exit_err; > - } > - > - mmap_read_unlock(mm); > - fput(exe_file); > - } > - > - err = 0; > - /* set the new file, lockless */ > - get_file(exe.file); > - old_exe = xchg(&mm->exe_file, exe.file); > - if (old_exe) > - fput(old_exe); > + err = atomic_set_mm_exe_file(mm, exe.file); > exit: > fdput(exe); > return err; > -exit_err: > - mmap_read_unlock(mm); > - fput(exe_file); > - goto exit; > } > > /* > -- > 2.31.1 >
diff --git a/include/linux/mm.h b/include/linux/mm.h index 7ca22e6e694a..197505324b74 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2581,6 +2581,8 @@ extern int mm_take_all_locks(struct mm_struct *mm); extern void mm_drop_all_locks(struct mm_struct *mm); extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file); +extern int atomic_set_mm_exe_file(struct mm_struct *mm, + struct file *new_exe_file); extern struct file *get_mm_exe_file(struct mm_struct *mm); extern struct file *get_task_exe_file(struct task_struct *task); diff --git a/kernel/fork.c b/kernel/fork.c index bc94b2cc5995..6bd2e52bcdfb 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1149,8 +1149,8 @@ void mmput_async(struct mm_struct *mm) * Main users are mmput() and sys_execve(). Callers prevent concurrent * invocations: in mmput() nobody alive left, in execve task is single * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the - * mm->exe_file, but does so without using set_mm_exe_file() in order - * to avoid the need for any locks. + * mm->exe_file, but uses atomic_set_mm_exe_file(), avoiding the need + * for any locks. */ void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) { @@ -1170,6 +1170,37 @@ void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) fput(old_exe_file); } +int atomic_set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file) +{ + struct vm_area_struct *vma; + struct file *old_exe_file; + int ret = 0; + + /* Forbid mm->exe_file change if old file still mapped. */ + old_exe_file = get_mm_exe_file(mm); + if (old_exe_file) { + mmap_read_lock(mm); + for (vma = mm->mmap; vma && !ret; vma = vma->vm_next) { + if (!vma->vm_file) + continue; + if (path_equal(&vma->vm_file->f_path, + &old_exe_file->f_path)) + ret = -EBUSY; + } + mmap_read_unlock(mm); + fput(old_exe_file); + if (ret) + return ret; + } + + /* set the new file, lockless */ + get_file(new_exe_file); + old_exe_file = xchg(&mm->exe_file, new_exe_file); + if (old_exe_file) + fput(old_exe_file); + return 0; +} + /** * get_mm_exe_file - acquire a reference to the mm's executable file * diff --git a/kernel/sys.c b/kernel/sys.c index ef1a78f5d71c..40551b411fda 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1846,7 +1846,6 @@ SYSCALL_DEFINE1(umask, int, mask) static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) { struct fd exe; - struct file *old_exe, *exe_file; struct inode *inode; int err; @@ -1869,40 +1868,10 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) if (err) goto exit; - /* - * Forbid mm->exe_file change if old file still mapped. - */ - exe_file = get_mm_exe_file(mm); - err = -EBUSY; - if (exe_file) { - struct vm_area_struct *vma; - - mmap_read_lock(mm); - for (vma = mm->mmap; vma; vma = vma->vm_next) { - if (!vma->vm_file) - continue; - if (path_equal(&vma->vm_file->f_path, - &exe_file->f_path)) - goto exit_err; - } - - mmap_read_unlock(mm); - fput(exe_file); - } - - err = 0; - /* set the new file, lockless */ - get_file(exe.file); - old_exe = xchg(&mm->exe_file, exe.file); - if (old_exe) - fput(old_exe); + err = atomic_set_mm_exe_file(mm, exe.file); exit: fdput(exe); return err; -exit_err: - mmap_read_unlock(mm); - fput(exe_file); - goto exit; } /*
Let's factor the main logic out into atomic_set_mm_exe_file(), such that all mm->exe_file logic is contained in kernel/fork.c. While at it, perform some simple cleanups that are possible now that we're simplifying the individual functions. Signed-off-by: David Hildenbrand <david@redhat.com> --- include/linux/mm.h | 2 ++ kernel/fork.c | 35 +++++++++++++++++++++++++++++++++-- kernel/sys.c | 33 +-------------------------------- 3 files changed, 36 insertions(+), 34 deletions(-)