This is a note to let you know that I've just added the patch titled
staging: android: ashmem: Fix lockdep issue during llseek
to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
staging-android-ashmem-fix-lockdep-issue-during-llseek.patch
and it can be found in the queue-4.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From cb57469c9573f6018cd1302953dd45d6e05aba7b Mon Sep 17 00:00:00 2001
From: Joel Fernandes <joelaf@xxxxxxxxxx>
Date: Fri, 16 Feb 2018 11:02:01 -0800
Subject: staging: android: ashmem: Fix lockdep issue during llseek
From: Joel Fernandes <joelaf@xxxxxxxxxx>
commit cb57469c9573f6018cd1302953dd45d6e05aba7b upstream.
ashmem_mutex create a chain of dependencies like so:
(1)
mmap syscall ->
mmap_sem -> (acquired)
ashmem_mmap
ashmem_mutex (try to acquire)
(block)
(2)
llseek syscall ->
ashmem_llseek ->
ashmem_mutex -> (acquired)
inode_lock ->
inode->i_rwsem (try to acquire)
(block)
(3)
getdents ->
iterate_dir ->
inode_lock ->
inode->i_rwsem (acquired)
copy_to_user ->
mmap_sem (try to acquire)
There is a lock ordering created between mmap_sem and inode->i_rwsem
causing a lockdep splat [2] during a syzcaller test, this patch fixes
the issue by unlocking the mutex earlier. Functionally that's Ok since
we don't need to protect vfs_llseek.
[1] https://patchwork.kernel.org/patch/10185031/
[2] https://lkml.org/lkml/2018/1/10/48
Acked-by: Todd Kjos <tkjos@xxxxxxxxxx>
Cc: Arve Hjonnevag <arve@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: syzbot+8ec30bb7bf1a981a2012@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
Acked-by: Greg Hackmann <ghackmann@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/android/ashmem.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -334,24 +334,23 @@ static loff_t ashmem_llseek(struct file
mutex_lock(&ashmem_mutex);
if (asma->size == 0) {
- ret = -EINVAL;
- goto out;
+ mutex_unlock(&ashmem_mutex);
+ return -EINVAL;
}
if (!asma->file) {
- ret = -EBADF;
- goto out;
+ mutex_unlock(&ashmem_mutex);
+ return -EBADF;
}
+ mutex_unlock(&ashmem_mutex);
+
ret = vfs_llseek(asma->file, offset, origin);
if (ret < 0)
- goto out;
+ return ret;
/** Copy f_pos from backing file, since f_ops->llseek() sets it */
file->f_pos = asma->file->f_pos;
-
-out:
- mutex_unlock(&ashmem_mutex);
return ret;
}
Patches currently in stable-queue which might be from joelaf@xxxxxxxxxx are
queue-4.15/staging-android-ashmem-fix-lockdep-issue-during-llseek.patch